完美解决关于禁止ViewPager预加载的相关问题
程序员文章站
2023-12-18 22:33:58
我最近上班又遇到一个小难题了，就是如题所述：viewpager预加载的问题。相信用过viewpager的人大抵都有遇到过这种情况，网上的解决办法也就那么几个，终于在我自己不...
我最近上班又遇到一个小难题了，就是如题所述：viewpager预加载的问题。相信用过viewpager的人大抵都有遇到过这种情况，网上的解决办法也就那么几个，终于在我自己不断试验之下，完美解决了（禁止了）viewpager的预加载。
好了，首先来说明一下，什么是viewpager的预加载：viewpager有一个 “预加载”的机制，默认会把viewpager当前位置的左右相邻页面预先初始化（俗称的预加载），它的默认值是 1，这样做的好处就是viewpager左右滑动会更加流畅。
可是我的情况很特殊，因为我 5 个fragment里有一个fragment是有surfaceview的，这样造成的问题就是，我viewpager滑动到其相邻页面时，含有surfaceview的页面就会被预先初始化，然后surfaceview就开始预览了，只是我们看不到而已。同样的，当我们从含有surfaceview的页面滑倒其相邻的页面时，surfaceview并不会回调其surfacedestory方法。于是这给我造成了极大的困扰。
ok，下面言归正传，到底该怎么禁止viewpager的这个预加载问题呢？
方案1：网上大多数说法是 懒加载，即让viewpager预加载初始化ui，而具体一些数据，网络访问请求等延迟加载。这是靠fragment里有一个setuservisiblehint(boolean isvisibletouser)的方法，我们可以在这个方法里做判断，当其true可见时（即切换到某一个具体fragment）时才去加载数据，这样可以省流量。但这里并不满足我的需求，因为某一个fragment并不会在viewpager滑动到其相邻的fragment时销毁。这个只可以解决部分人问题。
首先我们来深入了解下viewpager的预加载机制：
上文提到过，viewpager默认预加载的数量是1，这一点我们可以在viewpager源码里看到。
default_offscreen_pages 这里就定义了默认值是1， 所以网上 有种解决方案 说调用viewpager的setoffscreenpagelimit(int limit)，来设置viewpager预加载的数量，但是这里很明确的告诉你，这种方案是不可行的，如下图viewpager源码：
我们可以看到，如果你调用该方法传进来的值小于1是无效的，会被强行的拽回1。而且default_offscreen_pages 这个值是private的，子类继承viewpager也是不可见的。
方案2：然后网上有第二种说法，自定义一个viewpager，把原生viewpager全拷过来，修改这个default_offscreen_pages 值为0。对，就是这种解决方案！！但是！！
但是！！！但是什么呢？但是我试过，没用。为什么呢？接下来就是本文的重点了。
因为现在android都6.0了，版本都老高了，其实android虽然每个版本都有v4包，但是这些v4包是有差异的。这就造成高版本v4包里的viewpager，即使你copy它，将其default_offscreen_pages的值改为0，还是不起作用的，其中的逻辑变了。具体哪里变了导致无效我也没有继续研究了，毕竟公司不会花时间让我研究这些啊。偷笑
完美解决方案：ok，所以关于禁止viewpager预加载的完美解决方案就是，使用低版本v4包里的viewpager，完全copy一份，将其中的default_offscreen_pages值改为0即可。博主亲测 api 14 即 android 4.0的v4包里viewpager 有效。
当然，谷歌既然有这么一种viewpager的机制肯定有它的道理，所以一般还是预加载的好。
最后，因为低版本的源码越来越少的人会去下载，这里直接把这个禁止了预加载的viewpager贴上来，需要的人就拿去吧。copy就能用了。
package com.plumcot.usb.view;
/*
* copyright (c) 2011 the android open source project
*
* licensed under the apache license, version 2.0 (the "license");
* you may not use this file except in compliance with the license.
* you may obtain a copy of the license at
*
* http://www.apache.org/licenses/license-2.0
*
* unless required by applicable law or agreed to in writing, software
* distributed under the license is distributed on an "as is" basis,
* without warranties or conditions of any kind, either express or implied.
* see the license for the specific language governing permissions and
* limitations under the license.
*/
import android.content.context;
import android.database.datasetobserver;
import android.graphics.canvas;
import android.graphics.rect;
import android.graphics.drawable.drawable;
import android.os.parcel;
import android.os.parcelable;
import android.os.systemclock;
import android.support.v4.os.parcelablecompat;
import android.support.v4.os.parcelablecompatcreatorcallbacks;
import android.support.v4.view.keyeventcompat;
import android.support.v4.view.motioneventcompat;
import android.support.v4.view.pageradapter;
import android.support.v4.view.velocitytrackercompat;
import android.support.v4.view.viewcompat;
import android.support.v4.view.viewconfigurationcompat;
import android.support.v4.widget.edgeeffectcompat;
import android.util.attributeset;
import android.util.log;
import android.view.focusfinder;
import android.view.keyevent;
import android.view.motionevent;
import android.view.soundeffectconstants;
import android.view.velocitytracker;
import android.view.view;
import android.view.viewconfiguration;
import android.view.viewgroup;
import android.view.viewparent;
import android.view.accessibility.accessibilityevent;
import android.view.animation.interpolator;
import android.widget.scroller;
import java.util.arraylist;
import java.util.collections;
import java.util.comparator;
/**
* layout manager that allows the user to flip left and right
* through pages of data. you supply an implementation of a
* {@link android.support.v4.view.pageradapter} to generate the pages that the view shows.
*
* <p>note this class is currently under early design and
* development. the api will likely change in later updates of
* the compatibility library, requiring changes to the source code
* of apps when they are compiled against the newer version.</p>
*/
public class nopreloadviewpager extends viewgroup {
private static final string tag = "<span style="font-family:arial, helvetica, sans-serif;">nopreloadviewpager</span>";
private static final boolean debug = false;
private static final boolean use_cache = false;
private static final int default_offscreen_pages = 0;//默认是1
private static final int max_settle_duration = 600; // ms
static class iteminfo {
object object;
int position;
boolean scrolling;
}
private static final comparator<iteminfo> comparator = new comparator<iteminfo>(){
@override
public int compare(iteminfo lhs, iteminfo rhs) {
return lhs.position - rhs.position;
}};
private static final interpolator sinterpolator = new interpolator() {
public float getinterpolation(float t) {
// _o(t) = t * t * ((tension + 1) * t + tension)
// o(t) = _o(t - 1) + 1
t -= 1.0f;
return t * t * t + 1.0f;
}
};
private final arraylist<iteminfo> mitems = new arraylist<iteminfo>();
private pageradapter madapter;
private int mcuritem; // index of currently displayed page.
private int mrestoredcuritem = -1;
private parcelable mrestoredadapterstate = null;
private classloader mrestoredclassloader = null;
private scroller mscroller;
private pagerobserver mobserver;
private int mpagemargin;
private drawable mmargindrawable;
private int mchildwidthmeasurespec;
private int mchildheightmeasurespec;
private boolean minlayout;
private boolean mscrollingcacheenabled;
private boolean mpopulatepending;
private boolean mscrolling;
private int moffscreenpagelimit = default_offscreen_pages;
private boolean misbeingdragged;
private boolean misunabletodrag;
private int mtouchslop;
private float minitialmotionx;
/**
* position of the last motion event.
*/
private float mlastmotionx;
private float mlastmotiony;
/**
* id of the active pointer. this is used to retain consistency during
* drags/flings if multiple pointers are used.
*/
private int mactivepointerid = invalid_pointer;
/**
* sentinel value for no current active pointer.
* used by {@link #mactivepointerid}.
*/
private static final int invalid_pointer = -1;
/**
* determines speed during touch scrolling
*/
private velocitytracker mvelocitytracker;
private int mminimumvelocity;
private int mmaximumvelocity;
private float mbaselineflingvelocity;
private float mflingvelocityinfluence;
private boolean mfakedragging;
private long mfakedragbegintime;
private edgeeffectcompat mleftedge;
private edgeeffectcompat mrightedge;
private boolean mfirstlayout = true;
private onpagechangelistener monpagechangelistener;
/**
* indicates that the pager is in an idle, settled state. the current page
* is fully in view and no animation is in progress.
*/
public static final int scroll_state_idle = 0;
/**
* indicates that the pager is currently being dragged by the user.
*/
public static final int scroll_state_dragging = 1;
/**
* indicates that the pager is in the process of settling to a final position.
*/
public static final int scroll_state_settling = 2;
private int mscrollstate = scroll_state_idle;
/**
* callback interface for responding to changing state of the selected page.
*/
public interface onpagechangelistener {
/**
* this method will be invoked when the current page is scrolled, either as part
* of a programmatically initiated smooth scroll or a user initiated touch scroll.
*
* @param position position index of the first page currently being displayed.
* page position+1 will be visible if positionoffset is nonzero.
* @param positionoffset value from [0, 1) indicating the offset from the page at position.
* @param positionoffsetpixels value in pixels indicating the offset from position.
*/
public void onpagescrolled(int position, float positionoffset, int positionoffsetpixels);
/**
* this method will be invoked when a new page becomes selected. animation is not
* necessarily complete.
*
* @param position position index of the new selected page.
*/
public void onpageselected(int position);
/**
* called when the scroll state changes. useful for discovering when the user
* begins dragging, when the pager is automatically settling to the current page,
* or when it is fully stopped/idle.
*
* @param state the new scroll state.
* @see android.support.v4.view.viewpager#scroll_state_idle
* @see android.support.v4.view.viewpager#scroll_state_dragging
* @see android.support.v4.view.viewpager#scroll_state_settling
*/
public void onpagescrollstatechanged(int state);
}
/**
* simple implementation of the {@link android.support.v4.view.lazyviewpager.onpagechangelistener} interface with stub
* implementations of each method. extend this if you do not intend to override
* every method of {@link android.support.v4.view.lazyviewpager.onpagechangelistener}.
*/
public static class simpleonpagechangelistener implements onpagechangelistener {
@override
public void onpagescrolled(int position, float positionoffset, int positionoffsetpixels) {
// this space for rent
}
@override
public void onpageselected(int position) {
// this space for rent
}
@override
public void onpagescrollstatechanged(int state) {
// this space for rent
}
}
public nopreloadviewpager(context context) {
super(context);
initviewpager();
}
public nopreloadviewpager(context context, attributeset attrs) {
super(context, attrs);
initviewpager();
}
void initviewpager() {
setwillnotdraw(false);
setdescendantfocusability(focus_after_descendants);
setfocusable(true);
final context context = getcontext();
mscroller = new scroller(context, sinterpolator);
final viewconfiguration configuration = viewconfiguration.get(context);
mtouchslop = viewconfigurationcompat.getscaledpagingtouchslop(configuration);
mminimumvelocity = configuration.getscaledminimumflingvelocity();
mmaximumvelocity = configuration.getscaledmaximumflingvelocity();
mleftedge = new edgeeffectcompat(context);
mrightedge = new edgeeffectcompat(context);
float density = context.getresources().getdisplaymetrics().density;
mbaselineflingvelocity = 2500.0f * density;
mflingvelocityinfluence = 0.4f;
}
private void setscrollstate(int newstate) {
if (mscrollstate == newstate) {
return;
}
mscrollstate = newstate;
if (monpagechangelistener != null) {
monpagechangelistener.onpagescrollstatechanged(newstate);
}
}
public void setadapter(pageradapter adapter) {
if (madapter != null) {
// madapter.unregisterdatasetobserver(mobserver);
madapter.startupdate(this);
for (int i = 0; i < mitems.size(); i++) {
final iteminfo ii = mitems.get(i);
madapter.destroyitem(this, ii.position, ii.object);
}
madapter.finishupdate(this);
mitems.clear();
removeallviews();
mcuritem = 0;
scrollto(0, 0);
}
madapter = adapter;
if (madapter != null) {
if (mobserver == null) {
mobserver = new pagerobserver();
}
// madapter.registerdatasetobserver(mobserver);
mpopulatepending = false;
if (mrestoredcuritem >= 0) {
madapter.restorestate(mrestoredadapterstate, mrestoredclassloader);
setcurrentiteminternal(mrestoredcuritem, false, true);
mrestoredcuritem = -1;
mrestoredadapterstate = null;
mrestoredclassloader = null;
} else {
populate();
}
}
}
public pageradapter getadapter() {
return madapter;
}
/**
* set the currently selected page. if the viewpager has already been through its first
* layout there will be a smooth animated transition between the current item and the
* specified item.
*
* @param item item index to select
*/
public void setcurrentitem(int item) {
mpopulatepending = false;
setcurrentiteminternal(item, !mfirstlayout, false);
}
/**
* set the currently selected page.
*
* @param item item index to select
* @param smoothscroll true to smoothly scroll to the new item, false to transition immediately
*/
public void setcurrentitem(int item, boolean smoothscroll) {
mpopulatepending = false;
setcurrentiteminternal(item, smoothscroll, false);
}
public int getcurrentitem() {
return mcuritem;
}
void setcurrentiteminternal(int item, boolean smoothscroll, boolean always) {
setcurrentiteminternal(item, smoothscroll, always, 0);
}
void setcurrentiteminternal(int item, boolean smoothscroll, boolean always, int velocity) {
if (madapter == null || madapter.getcount() <= 0) {
setscrollingcacheenabled(false);
return;
}
if (!always && mcuritem == item && mitems.size() != 0) {
setscrollingcacheenabled(false);
return;
}
if (item < 0) {
item = 0;
} else if (item >= madapter.getcount()) {
item = madapter.getcount() - 1;
}
final int pagelimit = moffscreenpagelimit;
if (item > (mcuritem + pagelimit) || item < (mcuritem - pagelimit)) {
// we are doing a jump by more than one page. to avoid
// glitches, we want to keep all current pages in the view
// until the scroll ends.
for (int i=0; i<mitems.size(); i++) {
mitems.get(i).scrolling = true;
}
}
final boolean dispatchselected = mcuritem != item;
mcuritem = item;
populate();
final int destx = (getwidth() + mpagemargin) * item;
if (smoothscroll) {
smoothscrollto(destx, 0, velocity);
if (dispatchselected && monpagechangelistener != null) {
monpagechangelistener.onpageselected(item);
}
} else {
if (dispatchselected && monpagechangelistener != null) {
monpagechangelistener.onpageselected(item);
}
completescroll();
scrollto(destx, 0);
}
}
public void setonpagechangelistener(onpagechangelistener listener) {
monpagechangelistener = listener;
}
/**
* returns the number of pages that will be retained to either side of the
* current page in the view hierarchy in an idle state. defaults to 1.
*
* @return how many pages will be kept offscreen on either side
* @see #setoffscreenpagelimit(int)
*/
public int getoffscreenpagelimit() {
return moffscreenpagelimit;
}
/**
* set the number of pages that should be retained to either side of the
* current page in the view hierarchy in an idle state. pages beyond this
* limit will be recreated from the adapter when needed.
*
* <p>this is offered as an optimization. if you know in advance the number
* of pages you will need to support or have lazy-loading mechanisms in place
* on your pages, tweaking this setting can have benefits in perceived smoothness
* of paging animations and interaction. if you have a small number of pages (3-4)
* that you can keep active all at once, less time will be spent in layout for
* newly created view subtrees as the user pages back and forth.</p>
*
* <p>you should keep this limit low, especially if your pages have complex layouts.
* this setting defaults to 1.</p>
*
* @param limit how many pages will be kept offscreen in an idle state.
*/
public void setoffscreenpagelimit(int limit) {
if (limit < default_offscreen_pages) {
log.w(tag, "requested offscreen page limit " + limit + " too small; defaulting to " +
default_offscreen_pages);
limit = default_offscreen_pages;
}
if (limit != moffscreenpagelimit) {
moffscreenpagelimit = limit;
populate();
}
}
/**
* set the margin between pages.
*
* @param marginpixels distance between adjacent pages in pixels
* @see #getpagemargin()
* @see #setpagemargindrawable(android.graphics.drawable.drawable)
* @see #setpagemargindrawable(int)
*/
public void setpagemargin(int marginpixels) {
final int oldmargin = mpagemargin;
mpagemargin = marginpixels;
final int width = getwidth();
recomputescrollposition(width, width, marginpixels, oldmargin);
requestlayout();
}
/**
* return the margin between pages.
*
* @return the size of the margin in pixels
*/
public int getpagemargin() {
return mpagemargin;
}
/**
* set a drawable that will be used to fill the margin between pages.
*
* @param d drawable to display between pages
*/
public void setpagemargindrawable(drawable d) {
mmargindrawable = d;
if (d != null) refreshdrawablestate();
setwillnotdraw(d == null);
invalidate();
}
/**
* set a drawable that will be used to fill the margin between pages.
*
* @param resid resource id of a drawable to display between pages
*/
public void setpagemargindrawable(int resid) {
setpagemargindrawable(getcontext().getresources().getdrawable(resid));
}
@override
protected boolean verifydrawable(drawable who) {
return super.verifydrawable(who) || who == mmargindrawable;
}
@override
protected void drawablestatechanged() {
super.drawablestatechanged();
final drawable d = mmargindrawable;
if (d != null && d.isstateful()) {
d.setstate(getdrawablestate());
}
}
// we want the duration of the page snap animation to be influenced by the distance that
// the screen has to travel, however, we don't want this duration to be effected in a
// purely linear fashion. instead, we use this method to moderate the effect that the distance
// of travel has on the overall snap duration.
float distanceinfluenceforsnapduration(float f) {
f -= 0.5f; // center the values about 0.
f *= 0.3f * math.pi / 2.0f;
return (float) math.sin(f);
}
/**
* like {@link android.view.view#scrollby}, but scroll smoothly instead of immediately.
*
* @param x the number of pixels to scroll by on the x axis
* @param y the number of pixels to scroll by on the y axis
*/
void smoothscrollto(int x, int y) {
smoothscrollto(x, y, 0);
}
/**
* like {@link android.view.view#scrollby}, but scroll smoothly instead of immediately.
*
* @param x the number of pixels to scroll by on the x axis
* @param y the number of pixels to scroll by on the y axis
* @param velocity the velocity associated with a fling, if applicable. (0 otherwise)
*/
void smoothscrollto(int x, int y, int velocity) {
if (getchildcount() == 0) {
// nothing to do.
setscrollingcacheenabled(false);
return;
}
int sx = getscrollx();
int sy = getscrolly();
int dx = x - sx;
int dy = y - sy;
if (dx == 0 && dy == 0) {
completescroll();
setscrollstate(scroll_state_idle);
return;
}
setscrollingcacheenabled(true);
mscrolling = true;
setscrollstate(scroll_state_settling);
final float pagedelta = (float) math.abs(dx) / (getwidth() + mpagemargin);
int duration = (int) (pagedelta * 100);
velocity = math.abs(velocity);
if (velocity > 0) {
duration += (duration / (velocity / mbaselineflingvelocity)) * mflingvelocityinfluence;
} else {
duration += 100;
}
duration = math.min(duration, max_settle_duration);
mscroller.startscroll(sx, sy, dx, dy, duration);
invalidate();
}
void addnewitem(int position, int index) {
iteminfo ii = new iteminfo();
ii.position = position;
ii.object = madapter.instantiateitem(this, position);
if (index < 0) {
mitems.add(ii);
} else {
mitems.add(index, ii);
}
}
void datasetchanged() {
// this method only gets called if our observer is attached, so madapter is non-null.
boolean needpopulate = mitems.size() < 3 && mitems.size() < madapter.getcount();
int newcurritem = -1;
for (int i = 0; i < mitems.size(); i++) {
final iteminfo ii = mitems.get(i);
final int newpos = madapter.getitemposition(ii.object);
if (newpos == pageradapter.position_unchanged) {
continue;
}
if (newpos == pageradapter.position_none) {
mitems.remove(i);
i--;
madapter.destroyitem(this, ii.position, ii.object);
needpopulate = true;
if (mcuritem == ii.position) {
// keep the current item in the valid range
newcurritem = math.max(0, math.min(mcuritem, madapter.getcount() - 1));
}
continue;
}
if (ii.position != newpos) {
if (ii.position == mcuritem) {
// our current item changed position. follow it.
newcurritem = newpos;
}
ii.position = newpos;
needpopulate = true;
}
}
collections.sort(mitems, comparator);
if (newcurritem >= 0) {
// todo this currently causes a jump.
setcurrentiteminternal(newcurritem, false, true);
needpopulate = true;
}
if (needpopulate) {
populate();
requestlayout();
}
}
void populate() {
if (madapter == null) {
return;
}
// bail now if we are waiting to populate. this is to hold off
// on creating views from the time the user releases their finger to
// fling to a new position until we have finished the scroll to
// that position, avoiding glitches from happening at that point.
if (mpopulatepending) {
if (debug) log.i(tag, "populate is pending, skipping for now...");
return;
}
// also, don't populate until we are attached to a window. this is to
// avoid trying to populate before we have restored our view hierarchy
// state and conflicting with what is restored.
if (getwindowtoken() == null) {
return;
}
madapter.startupdate(this);
final int pagelimit = moffscreenpagelimit;
final int startpos = math.max(0, mcuritem - pagelimit);
final int n = madapter.getcount();
final int endpos = math.min(n-1, mcuritem + pagelimit);
if (debug) log.v(tag, "populating: startpos=" + startpos + " endpos=" + endpos);
// add and remove pages in the existing list.
int lastpos = -1;
for (int i=0; i<mitems.size(); i++) {
iteminfo ii = mitems.get(i);
if ((ii.position < startpos || ii.position > endpos) && !ii.scrolling) {
if (debug) log.i(tag, "removing: " + ii.position + " @ " + i);
mitems.remove(i);
i--;
madapter.destroyitem(this, ii.position, ii.object);
} else if (lastpos < endpos && ii.position > startpos) {
// the next item is outside of our range, but we have a gap
// between it and the last item where we want to have a page
// shown. fill in the gap.
lastpos++;
if (lastpos < startpos) {
lastpos = startpos;
}
while (lastpos <= endpos && lastpos < ii.position) {
if (debug) log.i(tag, "inserting: " + lastpos + " @ " + i);
addnewitem(lastpos, i);
lastpos++;
i++;
}
}
lastpos = ii.position;
}
// add any new pages we need at the end.
lastpos = mitems.size() > 0 ? mitems.get(mitems.size()-1).position : -1;
if (lastpos < endpos) {
lastpos++;
lastpos = lastpos > startpos ? lastpos : startpos;
while (lastpos <= endpos) {
if (debug) log.i(tag, "appending: " + lastpos);
addnewitem(lastpos, -1);
lastpos++;
}
}
if (debug) {
log.i(tag, "current page list:");
for (int i=0; i<mitems.size(); i++) {
log.i(tag, "#" + i + ": page " + mitems.get(i).position);
}
}
iteminfo curitem = null;
for (int i=0; i<mitems.size(); i++) {
if (mitems.get(i).position == mcuritem) {
curitem = mitems.get(i);
break;
}
}
madapter.setprimaryitem(this, mcuritem, curitem != null ? curitem.object : null);
madapter.finishupdate(this);
if (hasfocus()) {
view currentfocused = findfocus();
iteminfo ii = currentfocused != null ? infoforanychild(currentfocused) : null;
if (ii == null || ii.position != mcuritem) {
for (int i=0; i<getchildcount(); i++) {
view child = getchildat(i);
ii = infoforchild(child);
if (ii != null && ii.position == mcuritem) {
if (child.requestfocus(focus_forward)) {
break;
}
}
}
}
}
}
public static class savedstate extends basesavedstate {
int position;
parcelable adapterstate;
classloader loader;
public savedstate(parcelable superstate) {
super(superstate);
}
@override
public void writetoparcel(parcel out, int flags) {
super.writetoparcel(out, flags);
out.writeint(position);
out.writeparcelable(adapterstate, flags);
}
@override
public string tostring() {
return "fragmentpager.savedstate{"
+ integer.tohexstring(system.identityhashcode(this))
+ " position=" + position + "}";
}
public static final creator<savedstate> creator
= parcelablecompat.newcreator(new parcelablecompatcreatorcallbacks<savedstate>() {
@override
public savedstate createfromparcel(parcel in, classloader loader) {
return new savedstate(in, loader);
}
@override
public savedstate[] newarray(int size) {
return new savedstate[size];
}
});
savedstate(parcel in, classloader loader) {
super(in);
if (loader == null) {
loader = getclass().getclassloader();
}
position = in.readint();
adapterstate = in.readparcelable(loader);
this.loader = loader;
}
}
@override
public parcelable onsaveinstancestate() {
parcelable superstate = super.onsaveinstancestate();
savedstate ss = new savedstate(superstate);
ss.position = mcuritem;
if (madapter != null) {
ss.adapterstate = madapter.savestate();
}
return ss;
}
@override
public void onrestoreinstancestate(parcelable state) {
if (!(state instanceof savedstate)) {
super.onrestoreinstancestate(state);
return;
}
savedstate ss = (savedstate)state;
super.onrestoreinstancestate(ss.getsuperstate());
if (madapter != null) {
madapter.restorestate(ss.adapterstate, ss.loader);
setcurrentiteminternal(ss.position, false, true);
} else {
mrestoredcuritem = ss.position;
mrestoredadapterstate = ss.adapterstate;
mrestoredclassloader = ss.loader;
}
}
@override
public void addview(view child, int index, layoutparams params) {
if (minlayout) {
addviewinlayout(child, index, params);
child.measure(mchildwidthmeasurespec, mchildheightmeasurespec);
} else {
super.addview(child, index, params);
}
if (use_cache) {
if (child.getvisibility() != gone) {
child.setdrawingcacheenabled(mscrollingcacheenabled);
} else {
child.setdrawingcacheenabled(false);
}
}
}
iteminfo infoforchild(view child) {
for (int i=0; i<mitems.size(); i++) {
iteminfo ii = mitems.get(i);
if (madapter.isviewfromobject(child, ii.object)) {
return ii;
}
}
return null;
}
iteminfo infoforanychild(view child) {
viewparent parent;
while ((parent=child.getparent()) != this) {
if (parent == null || !(parent instanceof view)) {
return null;
}
child = (view)parent;
}
return infoforchild(child);
}
@override
protected void onattachedtowindow() {
super.onattachedtowindow();
mfirstlayout = true;
}
@override
protected void onmeasure(int widthmeasurespec, int heightmeasurespec) {
// for simple implementation, or internal size is always 0.
// we depend on the container to specify the layout size of
// our view. we can't really know what it is since we will be
// adding and removing different arbitrary views and do not
// want the layout to change as this happens.
setmeasureddimension(getdefaultsize(0, widthmeasurespec),
getdefaultsize(0, heightmeasurespec));
// children are just made to fill our space.
mchildwidthmeasurespec = measurespec.makemeasurespec(getmeasuredwidth() -
getpaddingleft() - getpaddingright(), measurespec.exactly);
mchildheightmeasurespec = measurespec.makemeasurespec(getmeasuredheight() -
getpaddingtop() - getpaddingbottom(), measurespec.exactly);
// make sure we have created all fragments that we need to have shown.
minlayout = true;
populate();
minlayout = false;
// make sure all children have been properly measured.
final int size = getchildcount();
for (int i = 0; i < size; ++i) {
final view child = getchildat(i);
if (child.getvisibility() != gone) {
if (debug) log.v(tag, "measuring #" + i + " " + child
+ ": " + mchildwidthmeasurespec);
child.measure(mchildwidthmeasurespec, mchildheightmeasurespec);
}
}
}
@override
protected void onsizechanged(int w, int h, int oldw, int oldh) {
super.onsizechanged(w, h, oldw, oldh);
// make sure scroll position is set correctly.
if (w != oldw) {
recomputescrollposition(w, oldw, mpagemargin, mpagemargin);
}
}
private void recomputescrollposition(int width, int oldwidth, int margin, int oldmargin) {
final int widthwithmargin = width + margin;
if (oldwidth > 0) {
final int oldscrollpos = getscrollx();
final int oldwwm = oldwidth + oldmargin;
final int oldscrollitem = oldscrollpos / oldwwm;
final float scrolloffset = (float) (oldscrollpos % oldwwm) / oldwwm;
final int scrollpos = (int) ((oldscrollitem + scrolloffset) * widthwithmargin);
scrollto(scrollpos, getscrolly());
if (!mscroller.isfinished()) {
// we now return to your regularly scheduled scroll, already in progress.
final int newduration = mscroller.getduration() - mscroller.timepassed();
mscroller.startscroll(scrollpos, 0, mcuritem * widthwithmargin, 0, newduration);
}
} else {
int scrollpos = mcuritem * widthwithmargin;
if (scrollpos != getscrollx()) {
completescroll();
scrollto(scrollpos, getscrolly());
}
}
}
@override
protected void onlayout(boolean changed, int l, int t, int r, int b) {
minlayout = true;
populate();
minlayout = false;
final int count = getchildcount();
final int width = r-l;
for (int i = 0; i < count; i++) {
view child = getchildat(i);
iteminfo ii;
if (child.getvisibility() != gone && (ii=infoforchild(child)) != null) {
int loff = (width + mpagemargin) * ii.position;
int childleft = getpaddingleft() + loff;
int childtop = getpaddingtop();
if (debug) log.v(tag, "positioning #" + i + " " + child + " f=" + ii.object
+ ":" + childleft + "," + childtop + " " + child.getmeasuredwidth()
+ "x" + child.getmeasuredheight());
child.layout(childleft, childtop,
childleft + child.getmeasuredwidth(),
childtop + child.getmeasuredheight());
}
}
mfirstlayout = false;
}
@override
public void computescroll() {
if (debug) log.i(tag, "computescroll: finished=" + mscroller.isfinished());
if (!mscroller.isfinished()) {
if (mscroller.computescrolloffset()) {
if (debug) log.i(tag, "computescroll: still scrolling");
int oldx = getscrollx();
int oldy = getscrolly();
int x = mscroller.getcurrx();
int y = mscroller.getcurry();
if (oldx != x || oldy != y) {
scrollto(x, y);
}
if (monpagechangelistener != null) {
final int widthwithmargin = getwidth() + mpagemargin;
final int position = x / widthwithmargin;
final int offsetpixels = x % widthwithmargin;
final float offset = (float) offsetpixels / widthwithmargin;
monpagechangelistener.onpagescrolled(position, offset, offsetpixels);
}
// keep on drawing until the animation has finished.
invalidate();
return;
}
}
// done with scroll, clean up state.
completescroll();
}
private void completescroll() {
boolean needpopulate = mscrolling;
if (needpopulate) {
// done with scroll, no longer want to cache view drawing.
setscrollingcacheenabled(false);
mscroller.abortanimation();
int oldx = getscrollx();
int oldy = getscrolly();
int x = mscroller.getcurrx();
int y = mscroller.getcurry();
if (oldx != x || oldy != y) {
scrollto(x, y);
}
setscrollstate(scroll_state_idle);
}
mpopulatepending = false;
mscrolling = false;
for (int i=0; i<mitems.size(); i++) {
iteminfo ii = mitems.get(i);
if (ii.scrolling) {
needpopulate = true;
ii.scrolling = false;
}
}
if (needpopulate) {
populate();
}
}
@override
public boolean onintercepttouchevent(motionevent ev) {
/*
* this method just determines whether we want to intercept the motion.
* if we return true, onmotionevent will be called and we do the actual
* scrolling there.
*/
final int action = ev.getaction() & motioneventcompat.action_mask;
// always take care of the touch gesture being complete.
if (action == motionevent.action_cancel || action == motionevent.action_up) {
// release the drag.
if (debug) log.v(tag, "intercept done!");
misbeingdragged = false;
misunabletodrag = false;
mactivepointerid = invalid_pointer;
return false;
}
// nothing more to do here if we have decided whether or not we
// are dragging.
if (action != motionevent.action_down) {
if (misbeingdragged) {
if (debug) log.v(tag, "intercept returning true!");
return true;
}
if (misunabletodrag) {
if (debug) log.v(tag, "intercept returning false!");
return false;
}
}
switch (action) {
case motionevent.action_move: {
/*
* misbeingdragged == false, otherwise the shortcut would have caught it. check
* whether the user has moved far enough from his original down touch.
*/
/*
* locally do absolute value. mlastmotiony is set to the y value
* of the down event.
*/
final int activepointerid = mactivepointerid;
if (activepointerid == invalid_pointer) {
// if we don't have a valid id, the touch down wasn't on content.
break;
}
final int pointerindex = motioneventcompat.findpointerindex(ev, activepointerid);
final float x = motioneventcompat.getx(ev, pointerindex);
final float dx = x - mlastmotionx;
final float xdiff = math.abs(dx);
final float y = motioneventcompat.gety(ev, pointerindex);
final float ydiff = math.abs(y - mlastmotiony);
final int scrollx = getscrollx();
final boolean atedge = (dx > 0 && scrollx == 0) || (dx < 0 && madapter != null &&
scrollx >= (madapter.getcount() - 1) * getwidth() - 1);
if (debug) log.v(tag, "moved x to " + x + "," + y + " diff=" + xdiff + "," + ydiff);
if (canscroll(this, false, (int) dx, (int) x, (int) y)) {
// nested view has scrollable area under this point. let it be handled there.
minitialmotionx = mlastmotionx = x;
mlastmotiony = y;
return false;
}
if (xdiff > mtouchslop && xdiff > ydiff) {
if (debug) log.v(tag, "starting drag!");
misbeingdragged = true;
setscrollstate(scroll_state_dragging);
mlastmotionx = x;
setscrollingcacheenabled(true);
} else {
if (ydiff > mtouchslop) {
// the finger has moved enough in the vertical
// direction to be counted as a drag... abort
// any attempt to drag horizontally, to work correctly
// with children that have scrolling containers.
if (debug) log.v(tag, "starting unable to drag!");
misunabletodrag = true;
}
}
break;
}
case motionevent.action_down: {
/*
* remember location of down touch.
* action_down always refers to pointer index 0.
*/
mlastmotionx = minitialmotionx = ev.getx();
mlastmotiony = ev.gety();
mactivepointerid = motioneventcompat.getpointerid(ev, 0);
if (mscrollstate == scroll_state_settling) {
// let the user 'catch' the pager as it animates.
misbeingdragged = true;
misunabletodrag = false;
setscrollstate(scroll_state_dragging);
} else {
completescroll();
misbeingdragged = false;
misunabletodrag = false;
}
if (debug) log.v(tag, "down at " + mlastmotionx + "," + mlastmotiony
+ " misbeingdragged=" + misbeingdragged
+ "misunabletodrag=" + misunabletodrag);
break;
}
case motioneventcompat.action_pointer_up:
onsecondarypointerup(ev);
break;
}
/*
* the only time we want to intercept motion events is if we are in the
* drag mode.
*/
return misbeingdragged;
}
@override
public boolean ontouchevent(motionevent ev) {
if (mfakedragging) {
// a fake drag is in progress already, ignore this real one
// but still eat the touch events.
// (it is likely that the user is multi-touching the screen.)
return true;
}
if (ev.getaction() == motionevent.action_down && ev.getedgeflags() != 0) {
// don't handle edge touches immediately -- they may actually belong to one of our
// descendants.
return false;
}
if (madapter == null || madapter.getcount() == 0) {
// nothing to present or scroll; nothing to touch.
return false;
}
if (mvelocitytracker == null) {
mvelocitytracker = velocitytracker.obtain();
}
mvelocitytracker.addmovement(ev);
final int action = ev.getaction();
boolean needsinvalidate = false;
switch (action & motioneventcompat.action_mask) {
case motionevent.action_down: {
/*
* if being flinged and user touches, stop the fling. isfinished
* will be false if being flinged.
*/
completescroll();
// remember where the motion event started
mlastmotionx = minitialmotionx = ev.getx();
mactivepointerid = motioneventcompat.getpointerid(ev, 0);
break;
}
case motionevent.action_move:
if (!misbeingdragged) {
final int pointerindex = motioneventcompat.findpointerindex(ev, mactivepointerid);
final float x = motioneventcompat.getx(ev, pointerindex);
final float xdiff = math.abs(x - mlastmotionx);
final float y = motioneventcompat.gety(ev, pointerindex);
final float ydiff = math.abs(y - mlastmotiony);
if (debug) log.v(tag, "moved x to " + x + "," + y + " diff=" + xdiff + "," + ydiff);
if (xdiff > mtouchslop && xdiff > ydiff) {
if (debug) log.v(tag, "starting drag!");
misbeingdragged = true;
mlastmotionx = x;
setscrollstate(scroll_state_dragging);
setscrollingcacheenabled(true);
}
}
if (misbeingdragged) {
// scroll to follow the motion event
final int activepointerindex = motioneventcompat.findpointerindex(
ev, mactivepointerid);
final float x = motioneventcompat.getx(ev, activepointerindex);
final float deltax = mlastmotionx - x;
mlastmotionx = x;
float oldscrollx = getscrollx();
float scrollx = oldscrollx + deltax;
final int width = getwidth();
final int widthwithmargin = width + mpagemargin;
final int lastitemindex = madapter.getcount() - 1;
final float leftbound = math.max(0, (mcuritem - 1) * widthwithmargin);
final float rightbound =
math.min(mcuritem + 1, lastitemindex) * widthwithmargin;
if (scrollx < leftbound) {
if (leftbound == 0) {
float over = -scrollx;
needsinvalidate = mleftedge.onpull(over / width);
}
scrollx = leftbound;
} else if (scrollx > rightbound) {
if (rightbound == lastitemindex * widthwithmargin) {
float over = scrollx - rightbound;
needsinvalidate = mrightedge.onpull(over / width);
}
scrollx = rightbound;
}
// don't lose the rounded component
mlastmotionx += scrollx - (int) scrollx;
scrollto((int) scrollx, getscrolly());
if (monpagechangelistener != null) {
final int position = (int) scrollx / widthwithmargin;
final int positionoffsetpixels = (int) scrollx % widthwithmargin;
final float positionoffset = (float) positionoffsetpixels / widthwithmargin;
monpagechangelistener.onpagescrolled(position, positionoffset,
positionoffsetpixels);
}
}
break;
case motionevent.action_up:
if (misbeingdragged) {
final velocitytracker velocitytracker = mvelocitytracker;
velocitytracker.computecurrentvelocity(1000, mmaximumvelocity);
int initialvelocity = (int) velocitytrackercompat.getxvelocity(
velocitytracker, mactivepointerid);
mpopulatepending = true;
final int widthwithmargin = getwidth() + mpagemargin;
final int scrollx = getscrollx();
final int currentpage = scrollx / widthwithmargin;
int nextpage = initialvelocity > 0 ? currentpage : currentpage + 1;
setcurrentiteminternal(nextpage, true, true, initialvelocity);
mactivepointerid = invalid_pointer;
enddrag();
needsinvalidate = mleftedge.onrelease() | mrightedge.onrelease();
}
break;
case motionevent.action_cancel:
if (misbeingdragged) {
setcurrentiteminternal(mcuritem, true, true);
mactivepointerid = invalid_pointer;
enddrag();
needsinvalidate = mleftedge.onrelease() | mrightedge.onrelease();
}
break;
case motioneventcompat.action_pointer_down: {
final int index = motioneventcompat.getactionindex(ev);
final float x = motioneventcompat.getx(ev, index);
mlastmotionx = x;
mactivepointerid = motioneventcompat.getpointerid(ev, index);
break;
}
case motioneventcompat.action_pointer_up:
onsecondarypointerup(ev);
mlastmotionx = motioneventcompat.getx(ev,
motioneventcompat.findpointerindex(ev, mactivepointerid));
break;
}
if (needsinvalidate) {
invalidate();
}
return true;
}
@override
public void draw(canvas canvas) {
super.draw(canvas);
boolean needsinvalidate = false;
final int overscrollmode = viewcompat.getoverscrollmode(this);
if (overscrollmode == viewcompat.over_scroll_always ||
(overscrollmode == viewcompat.over_scroll_if_content_scrolls &&
madapter != null && madapter.getcount() > 1)) {
if (!mleftedge.isfinished()) {
final int restorecount = canvas.save();
final int height = getheight() - getpaddingtop() - getpaddingbottom();
canvas.rotate(270);
canvas.translate(-height + getpaddingtop(), 0);
mleftedge.setsize(height, getwidth());
needsinvalidate |= mleftedge.draw(canvas);
canvas.restoretocount(restorecount);
}
if (!mrightedge.isfinished()) {
final int restorecount = canvas.save();
final int width = getwidth();
final int height = getheight() - getpaddingtop() - getpaddingbottom();
final int itemcount = madapter != null ? madapter.getcount() : 1;
canvas.rotate(90);
canvas.translate(-getpaddingtop(),
-itemcount * (width + mpagemargin) + mpagemargin);
mrightedge.setsize(height, width);
needsinvalidate |= mrightedge.draw(canvas);
canvas.restoretocount(restorecount);
}
} else {
mleftedge.finish();
mrightedge.finish();
}
if (needsinvalidate) {
// keep animating
invalidate();
}
}
@override
protected void ondraw(canvas canvas) {
super.ondraw(canvas);
// draw the margin drawable if needed.
if (mpagemargin > 0 && mmargindrawable != null) {
final int scrollx = getscrollx();
final int width = getwidth();
final int offset = scrollx % (width + mpagemargin);
if (offset != 0) {
// pages fit completely when settled; we only need to draw when in between
final int left = scrollx - offset + width;
mmargindrawable.setbounds(left, 0, left + mpagemargin, getheight());
mmargindrawable.draw(canvas);
}
}
}
/**
* start a fake drag of the pager.
*
* <p>a fake drag can be useful if you want to synchronize the motion of the viewpager
* with the touch scrolling of another view, while still letting the viewpager
* control the snapping motion and fling behavior. (e.g. parallax-scrolling tabs.)
* call {@link #fakedragby(float)} to simulate the actual drag motion. call
* {@link #endfakedrag()} to complete the fake drag and fling as necessary.
*
* <p>during a fake drag the viewpager will ignore all touch events. if a real drag
* is already in progress, this method will return false.
*
* @return true if the fake drag began successfully, false if it could not be started.
*
* @see #fakedragby(float)
* @see #endfakedrag()
*/
public boolean beginfakedrag() {
if (misbeingdragged) {
return false;
}
mfakedragging = true;
setscrollstate(scroll_state_dragging);
minitialmotionx = mlastmotionx = 0;
if (mvelocitytracker == null) {
mvelocitytracker = velocitytracker.obtain();
} else {
mvelocitytracker.clear();
}
final long time = systemclock.uptimemillis();
final motionevent ev = motionevent.obtain(time, time, motionevent.action_down, 0, 0, 0);
mvelocitytracker.addmovement(ev);
ev.recycle();
mfakedragbegintime = time;
return true;
}
/**
* end a fake drag of the pager.
*
* @see #beginfakedrag()
* @see #fakedragby(float)
*/
public void endfakedrag() {
if (!mfakedragging) {
throw new illegalstateexception("no fake drag in progress. call beginfakedrag first.");
}
final velocitytracker velocitytracker = mvelocitytracker;
velocitytracker.computecurrentvelocity(1000, mmaximumvelocity);
int initialvelocity = (int)velocitytrackercompat.getyvelocity(
velocitytracker, mactivepointerid);
mpopulatepending = true;
if ((math.abs(initialvelocity) > mminimumvelocity)
|| math.abs(minitialmotionx-mlastmotionx) >= (getwidth()/3)) {
if (mlastmotionx > minitialmotionx) {
setcurrentiteminternal(mcuritem-1, true, true);
} else {
setcurrentiteminternal(mcuritem+1, true, true);
}
} else {
setcurrentiteminternal(mcuritem, true, true);
}
enddrag();
mfakedragging = false;
}
/**
* fake drag by an offset in pixels. you must have called {@link #beginfakedrag()} first.
*
* @param xoffset offset in pixels to drag by.
* @see #beginfakedrag()
* @see #endfakedrag()
*/
public void fakedragby(float xoffset) {
if (!mfakedragging) {
throw new illegalstateexception("no fake drag in progress. call beginfakedrag first.");
}
mlastmotionx += xoffset;
float scrollx = getscrollx() - xoffset;
final int width = getwidth();
final int widthwithmargin = width + mpagemargin;
final float leftbound = math.max(0, (mcuritem - 1) * widthwithmargin);
final float rightbound =
math.min(mcuritem + 1, madapter.getcount() - 1) * widthwithmargin;
if (scrollx < leftbound) {
scrollx = leftbound;
} else if (scrollx > rightbound) {
scrollx = rightbound;
}
// don't lose the rounded component
mlastmotionx += scrollx - (int) scrollx;
scrollto((int) scrollx, getscrolly());
if (monpagechangelistener != null) {
final int position = (int) scrollx / widthwithmargin;
final int positionoffsetpixels = (int) scrollx % widthwithmargin;
final float positionoffset = (float) positionoffsetpixels / widthwithmargin;
monpagechangelistener.onpagescrolled(position, positionoffset,
positionoffsetpixels);
}
// synthesize an event for the velocitytracker.
final long time = systemclock.uptimemillis();
final motionevent ev = motionevent.obtain(mfakedragbegintime, time, motionevent.action_move,
mlastmotionx, 0, 0);
mvelocitytracker.addmovement(ev);
ev.recycle();
}
/**
* returns true if a fake drag is in progress.
*
* @return true if currently in a fake drag, false otherwise.
*
* @see #beginfakedrag()
* @see #fakedragby(float)
* @see #endfakedrag()
*/
public boolean isfakedragging() {
return mfakedragging;
}
private void onsecondarypointerup(motionevent ev) {
final int pointerindex = motioneventcompat.getactionindex(ev);
final int pointerid = motioneventcompat.getpointerid(ev, pointerindex);
if (pointerid == mactivepointerid) {
// this was our active pointer going up. choose a new
// active pointer and adjust accordingly.
final int newpointerindex = pointerindex == 0 ? 1 : 0;
mlastmotionx = motioneventcompat.getx(ev, newpointerindex);
mactivepointerid = motioneventcompat.getpointerid(ev, newpointerindex);
if (mvelocitytracker != null) {
mvelocitytracker.clear();
}
}
}
private void enddrag() {
misbeingdragged = false;
misunabletodrag = false;
if (mvelocitytracker != null) {
mvelocitytracker.recycle();
mvelocitytracker = null;
}
}
private void setscrollingcacheenabled(boolean enabled) {
if (mscrollingcacheenabled != enabled) {
mscrollingcacheenabled = enabled;
if (use_cache) {
final int size = getchildcount();
for (int i = 0; i < size; ++i) {
final view child = getchildat(i);
if (child.getvisibility() != gone) {
child.setdrawingcacheenabled(enabled);
}
}
}
}
}
/**
* tests scrollability within child views of v given a delta of dx.
*
* @param v view to test for horizontal scrollability
* @param checkv whether the view v passed should itself be checked for scrollability (true),
* or just its children (false).
* @param dx delta scrolled in pixels
* @param x x coordinate of the active touch point
* @param y y coordinate of the active touch point
* @return true if child views of v can be scrolled by delta of dx.
*/
protected boolean canscroll(view v, boolean checkv, int dx, int x, int y) {
if (v instanceof viewgroup) {
final viewgroup group = (viewgroup) v;
final int scrollx = v.getscrollx();
final int scrolly = v.getscrolly();
final int count = group.getchildcount();
// count backwards - let topmost views consume scroll distance first.
for (int i = count - 1; i >= 0; i--) {
// todo: add versioned support here for transformed views.
// this will not work for transformed views in honeycomb+
final view child = group.getchildat(i);
if (x + scrollx >= child.getleft() && x + scrollx < child.getright() &&
y + scrolly >= child.gettop() && y + scrolly < child.getbottom() &&
canscroll(child, true, dx, x + scrollx - child.getleft(),
y + scrolly - child.gettop())) {
return true;
}
}
}
return checkv && viewcompat.canscrollhorizontally(v, -dx);
}
@override
public boolean dispatchkeyevent(keyevent event) {
// let the focused view and/or our descendants get the key first
return super.dispatchkeyevent(event) || executekeyevent(event);
}
/**
* you can call this function yourself to have the scroll view perform
* scrolling from a key event, just as if the event had been dispatched to
* it by the view hierarchy.
*
* @param event the key event to execute.
* @return return true if the event was handled, else false.
*/
public boolean executekeyevent(keyevent event) {
boolean handled = false;
if (event.getaction() == keyevent.action_down) {
switch (event.getkeycode()) {
case keyevent.keycode_dpad_left:
handled = arrowscroll(focus_left);
break;
case keyevent.keycode_dpad_right:
handled = arrowscroll(focus_right);
break;
case keyevent.keycode_tab:
if (keyeventcompat.hasnomodifiers(event)) {
handled = arrowscroll(focus_forward);
} else if (keyeventcompat.hasmodifiers(event, keyevent.meta_shift_on)) {
handled = arrowscroll(focus_backward);
}
break;
}
}
return handled;
}
public boolean arrowscroll(int direction) {
view currentfocused = findfocus();
if (currentfocused == this) currentfocused = null;
boolean handled = false;
view nextfocused = focusfinder.getinstance().findnextfocus(this, currentfocused,
direction);
if (nextfocused != null && nextfocused != currentfocused) {
if (direction == view.focus_left) {
// if there is nothing to the left, or this is causing us to
// jump to the right, then what we really want to do is page left.
if (currentfocused != null && nextfocused.getleft() >= currentfocused.getleft()) {
handled = pageleft();
} else {
handled = nextfocused.requestfocus();
}
} else if (direction == view.focus_right) {
// if there is nothing to the right, or this is causing us to
// jump to the left, then what we really want to do is page right.
if (currentfocused != null && nextfocused.getleft() <= currentfocused.getleft()) {
handled = pageright();
} else {
handled = nextfocused.requestfocus();
}
}
} else if (direction == focus_left || direction == focus_backward) {
// trying to move left and nothing there; try to page.
handled = pageleft();
} else if (direction == focus_right || direction == focus_forward) {
// trying to move right and nothing there; try to page.
handled = pageright();
}
if (handled) {
playsoundeffect(soundeffectconstants.getcontantforfocusdirection(direction));
}
return handled;
}
boolean pageleft() {
if (mcuritem > 0) {
setcurrentitem(mcuritem-1, true);
return true;
}
return false;
}
boolean pageright() {
if (madapter != null && mcuritem < (madapter.getcount()-1)) {
setcurrentitem(mcuritem+1, true);
return true;
}
return false;
}
/**
* we only want the current page that is being shown to be focusable.
*/
@override
public void addfocusables(arraylist<view> views, int direction, int focusablemode) {
final int focusablecount = views.size();
final int descendantfocusability = getdescendantfocusability();
if (descendantfocusability != focus_block_descendants) {
for (int i = 0; i < getchildcount(); i++) {
final view child = getchildat(i);
if (child.getvisibility() == visible) {
iteminfo ii = infoforchild(child);
if (ii != null && ii.position == mcuritem) {
child.addfocusables(views, direction, focusablemode);
}
}
}
}
// we add ourselves (if focusable) in all cases except for when we are
// focus_after_descendants and there are some descendants focusable. this is
// to avoid the focus search finding layouts when a more precise search
// among the focusable children would be more interesting.
if (
descendantfocusability != focus_after_descendants ||
// no focusable descendants
(focusablecount == views.size())) {
// note that we can't call the superclass here, because it will
// add all views in. so we need to do the same thing view does.
if (!isfocusable()) {
return;
}
if ((focusablemode & focusables_touch_mode) == focusables_touch_mode &&
isintouchmode() && !isfocusableintouchmode()) {
return;
}
if (views != null) {
views.add(this);
}
}
}
/**
* we only want the current page that is being shown to be touchable.
*/
@override
public void addtouchables(arraylist<view> views) {
// note that we don't call super.addtouchables(), which means that
// we don't call view.addtouchables(). this is okay because a viewpager
// is itself not touchable.
for (int i = 0; i < getchildcount(); i++) {
final view child = getchildat(i);
if (child.getvisibility() == visible) {
iteminfo ii = infoforchild(child);
if (ii != null && ii.position == mcuritem) {
child.addtouchables(views);
}
}
}
}
/**
* we only want the current page that is being shown to be focusable.
*/
@override
protected boolean onrequestfocusindescendants(int direction,
rect previouslyfocusedrect) {
int index;
int increment;
int end;
int count = getchildcount();
if ((direction & focus_forward) != 0) {
index = 0;
increment = 1;
end = count;
} else {
index = count - 1;
increment = -1;
end = -1;
}
for (int i = index; i != end; i += increment) {
view child = getchildat(i);
if (child.getvisibility() == visible) {
iteminfo ii = infoforchild(child);
if (ii != null && ii.position == mcuritem) {
if (child.requestfocus(direction, previouslyfocusedrect)) {
return true;
}
}
}
}
return false;
}
@override
public boolean dispatchpopulateaccessibilityevent(accessibilityevent event) {
// viewpagers should only report accessibility info for the current page,
// otherwise things get very confusing.
// todo: should this note something about the paging container?
final int childcount = getchildcount();
for (int i = 0; i < childcount; i++) {
final view child = getchildat(i);
if (child.getvisibility() == visible) {
final iteminfo ii = infoforchild(child);
if (ii != null && ii.position == mcuritem &&
child.dispatchpopulateaccessibilityevent(event)) {
return true;
}
}
}
return false;
}
private class pagerobserver extends datasetobserver {
@override
public void onchanged() {
datasetchanged();
}
@override
public void oninvalidated() {
datasetchanged();
}
}
}
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。