Android6.0 固定屏幕功能实现方法及实例
android 固定屏幕功能
可能大家看到这个标题不知道是什么东西，我先说明下，android6.0在设置->安全->屏幕固定开启后，然后再长按home键出现最近的几个activity可以选择一个图钉按钮就开启了屏幕固定功能。
屏幕固定开启后，屏幕只能固定在设定的task上的activity切换。
一、设置固定屏幕
我们先来看systemui/src/com/android/systemui/recents/screenpinningrequest.java的代码，这段代码就是长按home键出现几个activity，然后按了图钉的那个按钮。在这里直接调用了ams的startlocktaskmodeoncurrent函数。
@override
public void onclick(view v) {
if (v.getid() == r.id.screen_pinning_ok_button || mrequestwindow == v) {
try {
activitymanagernative.getdefault().startlocktaskmodeoncurrent();
} catch (remoteexception e) {}
}
clearprompt();
}
我们来看ams的startlocktaskmodeoncurrent函数，先调用activitystacksupervisor的toprunningactivitylocked获取最前面的activity，然后调用startlocktaskmodelocked函数，参数是taskrecord。
public void startlocktaskmodeoncurrent() throws remoteexception {
enforcecallingpermission(android.manifest.permission.manage_activity_stacks,
"startlocktaskmodeoncurrent");
long ident = binder.clearcallingidentity();
try {
synchronized (this) {
activityrecord r = mstacksupervisor.toprunningactivitylocked();
if (r != null) {
startlocktaskmodelocked(r.task);
}
}
} finally {
binder.restorecallingidentity(ident);
}
}
我们再来看toprunningactivitylocked函数，先从mfocusedstack中获取最前面的activity。如果没有再遍历所有的mstacks获取。
activityrecord toprunningactivitylocked() {
final activitystack focusedstack = mfocusedstack;
activityrecord r = focusedstack.toprunningactivitylocked(null);
if (r != null) {
return r;
}
// return to the home stack.
final arraylist<activitystack> stacks = mhomestack.mstacks;
for (int stackndx = stacks.size() - 1; stackndx >= 0; --stackndx) {
final activitystack stack = stacks.get(stackndx);
if (stack != focusedstack && isfrontstack(stack)) {
r = stack.toprunningactivitylocked(null);
if (r != null) {
return r;
}
}
}
return null;
}
在startlocktaskmodelocked函数中主要是调用了activitystacksupervisor的setlocktaskmodelocked函数，下面我们来看这个函数，我们的task不为null，第一次mlocktaskmodetasks为空，会发送一个lock_task_start_msg消息
void setlocktaskmodelocked(taskrecord task, int locktaskmodestate, string reason,
boolean andresume) {
if (task == null) {
// take out of lock task mode if necessary
final taskrecord lockedtask = getlockedtasklocked();
if (lockedtask != null) {
removelockedtasklocked(lockedtask);
if (!mlocktaskmodetasks.isempty()) {
// there are locked tasks remaining, can only finish this task, not unlock it.
if (debug_locktask) slog.w(tag_locktask,
"setlocktaskmodelocked: tasks remaining, can't unlock");
lockedtask.performcleartasklocked();
resumetopactivitieslocked();
return;
}
}
if (debug_locktask) slog.w(tag_locktask,
"setlocktaskmodelocked: no tasks to unlock. callers=" + debug.getcallers(4));
return;
}
// should have already been checked, but do it again.
if (task.mlocktaskauth == lock_task_auth_dont_lock) {
if (debug_locktask) slog.w(tag_locktask,
"setlocktaskmodelocked: can't lock due to auth");
return;
}
if (islocktaskmodeviolation(task)) {
slog.e(tag_locktask, "setlocktaskmode: attempt to start an unauthorized lock task.");
return;
}
if (mlocktaskmodetasks.isempty()) {
// first locktask.
final message locktaskmsg = message.obtain();
locktaskmsg.obj = task.intent.getcomponent().getpackagename();
locktaskmsg.arg1 = task.userid;
locktaskmsg.what = lock_task_start_msg;//发送消息
locktaskmsg.arg2 = locktaskmodestate;
mhandler.sendmessage(locktaskmsg);
}
// add it or move it to the top.
if (debug_locktask) slog.w(tag_locktask, "setlocktaskmodelocked: locking to " + task +
" callers=" + debug.getcallers(4));
mlocktaskmodetasks.remove(task);
mlocktaskmodetasks.add(task);//加入到mlockmodetasks中
if (task.mlocktaskuid == -1) {
task.mlocktaskuid = task.effectiveuid;
}
if (andresume) {
findtasktomovetofrontlocked(task, 0, null, reason);//把task放最前面
resumetopactivitieslocked();//显示新的activity
}
}
我们再来看消息处理，在消息处理中主要调用了wms的disablekeyguard函数。
case lock_task_start_msg: {
// when lock task starts, we disable the status bars.
try {
if (mlocktasknotify == null) {
mlocktasknotify = new locktasknotify(mservice.mcontext);
}
mlocktasknotify.show(true);
mlocktaskmodestate = msg.arg2;
if (getstatusbarservice() != null) {
int flags = 0;
if (mlocktaskmodestate == lock_task_mode_locked) {
flags = statusbarmanager.disable_mask
& (~statusbarmanager.disable_back);
} else if (mlocktaskmodestate == lock_task_mode_pinned) {
flags = statusbarmanager.disable_mask
& (~statusbarmanager.disable_back)
& (~statusbarmanager.disable_home)
& (~statusbarmanager.disable_recent);
}
getstatusbarservice().disable(flags, mtoken,
mservice.mcontext.getpackagename());
}
mwindowmanager.disablekeyguard(mtoken, lock_task_tag);
if (getdevicepolicymanager() != null) {
getdevicepolicymanager().notifylocktaskmodechanged(true,
(string)msg.obj, msg.arg1);
}
} catch (remoteexception ex) {
throw new runtimeexception(ex);
}
} break;
二、固定屏幕后activity启动流程
在固定屏幕后，如果我们启动其他taskrecord的activity是不能启动的，我们来看下这个原理。在startactivityuncheckedlocked函数中会调用islocktaskmodeviolation函数来判断是否进一步的activity的启动流程，我们来看下这个函数，调用getlockedtasklocked来看mlocktaskmodetasks（就是锁定屏幕的那些task），如果当前的task就是当前正在固定屏幕的task，直接return false就是可以继续启动activity的流程，而如果不是，我们需要看task的mlocktaskauth变量。
boolean islocktaskmodeviolation(taskrecord task, boolean isnewcleartask) {
if (getlockedtasklocked() == task && !isnewcleartask) {
return false;
}
final int locktaskauth = task.mlocktaskauth;
switch (locktaskauth) {
case lock_task_auth_dont_lock:
return !mlocktaskmodetasks.isempty();
case lock_task_auth_launchable_priv:
case lock_task_auth_launchable:
case lock_task_auth_whitelisted:
return false;
case lock_task_auth_pinnable:
// pinnable tasks can't be launched on top of locktask tasks.
return !mlocktaskmodetasks.isempty();
default:
slog.w(tag, "islocktaskmodeviolation: invalid locktaskauth value=" + locktaskauth);
return true;
}
}
我们再来看taskrecord的setlockedtaskauth函数，在新建一个taskrecord的时候会调用setintent函数，而setintent函数又是在taskrecord的构造函数中调用的。我们来看这个函数mlocktaskauth的值是根据mlocktaskmode来定的，而mlocktaskmode又是activityinfo传入的，这个值是在pkms解析androidmanifest.xml的时候构造的，默认就是lock_task_launch_mode_default，而当没有白名单mlocktaskauth最后就是lock_task_auth_pinnable。
void setlocktaskauth() {
if (!mprivileged &&
(mlocktaskmode == lock_task_launch_mode_always ||
mlocktaskmode == lock_task_launch_mode_never)) {
// non-priv apps are not allowed to use always or never, fall back to default
mlocktaskmode = lock_task_launch_mode_default;
}
switch (mlocktaskmode) {
case lock_task_launch_mode_default:
mlocktaskauth = islocktaskwhitelistedlocked() ?
lock_task_auth_whitelisted : lock_task_auth_pinnable;
break;
case lock_task_launch_mode_never:
mlocktaskauth = lock_task_auth_dont_lock;
break;
case lock_task_launch_mode_always:
mlocktaskauth = lock_task_auth_launchable_priv;
break;
case lock_task_launch_mode_if_whitelisted:
mlocktaskauth = islocktaskwhitelistedlocked() ?
lock_task_auth_launchable : lock_task_auth_pinnable;
break;
}
if (debug_locktask) slog.d(tag_locktask, "setlocktaskauth: task=" + this +
" mlocktaskauth=" + locktaskauthtostring());
}
我们再来看islocktaskmodeviolation函数如下代码，现在是task的mlocktaskauth 是lock_task_auth_pinnable，而当前处于固定屏幕，所以mlocktaskmodetasks不为null，最后返回true。那activity启动流程就不能走下去了，那就是代表启动普通的activity会被阻止。
case lock_task_auth_pinnable: // pinnable tasks can't be launched on top of locktask tasks. return !mlocktaskmodetasks.isempty();
三、取消固定屏幕
最后我们再来看看取消固定屏幕，取消屏幕会在phonestatusbar中取消，但是一定是要有虚拟键，原生就是这么设定的。最后调用了ams的stoplocktaskmodeoncurrent函数。这个函数主要是调用了stoplocktaskmode函数，这个函数中主要是调用了activitystacksupervisor的setlocktaskmodelocked函数，之前在固定屏幕时也是调用了这个函数，但是这里我们仔细看，其第一个参数为null。
public void stoplocktaskmode() {
final taskrecord locktask = mstacksupervisor.getlockedtasklocked();
if (locktask == null) {
// our work here is done.
return;
}
final int callinguid = binder.getcallinguid();
final int locktaskuid = locktask.mlocktaskuid;
// ensure the same caller for startlocktaskmode and stoplocktaskmode.
// it is possible locktaskmode was started by the system process because
// android:locktaskmode is set to a locking value in the application manifest instead of
// the app calling startlocktaskmode. in this case {@link taskrecord.mlocktaskuid} will
// be 0, so we compare the callinguid to the {@link taskrecord.effectiveuid} instead.
if (getlocktaskmodestate() == activitymanager.lock_task_mode_locked &&
callinguid != locktaskuid
&& (locktaskuid != 0
|| (locktaskuid == 0 && callinguid != locktask.effectiveuid))) {
throw new securityexception("invalid uid, expected " + locktaskuid
+ " callinguid=" + callinguid + " effectiveuid=" + locktask.effectiveuid);
}
long ident = binder.clearcallingidentity();
try {
log.d(tag, "stoplocktaskmode");
// stop lock task
synchronized (this) {
mstacksupervisor.setlocktaskmodelocked(null, activitymanager.lock_task_mode_none,
"stoplocktask", true);
}
} finally {
binder.restorecallingidentity(ident);
}
}
我们来看下这个函数，如果为空，现在调用getlockedtasklocked获取当前固定屏幕的taskrecord，然后调用removelockedtasklocked去除这个taskrecord，如果还不为null，调用resumetopactivitieslocked启动下个activity（一般也就是下个屏幕锁定的taskrecord的activity）。
如果为空了，直接返回。但是在我们下次启动普通的activity的时候就恢复正常了，因为mlocktaskmodetasks已经为空了。
void setlocktaskmodelocked(taskrecord task, int locktaskmodestate, string reason,
boolean andresume) {
if (task == null) {
// take out of lock task mode if necessary
final taskrecord lockedtask = getlockedtasklocked();
if (lockedtask != null) {
removelockedtasklocked(lockedtask);
if (!mlocktaskmodetasks.isempty()) {
// there are locked tasks remaining, can only finish this task, not unlock it.
if (debug_locktask) slog.w(tag_locktask,
"setlocktaskmodelocked: tasks remaining, can't unlock");
lockedtask.performcleartasklocked();
resumetopactivitieslocked();
return;
}
}
if (debug_locktask) slog.w(tag_locktask,
"setlocktaskmodelocked: no tasks to unlock. callers=" + debug.getcallers(4));
return;
}
四、没有虚拟键如何取消屏幕固定
前面说过如果没有虚拟键就不能取消屏幕固定了，我们说下几种方式
1.使用am命令 am task lock stop可以调用am的stoplocktaskmode函数
2.另一种我们可以在activity.java中修改代码，比较长按返回键调用ams的stoplocktaskmode方法，下面就是实现，activity本身提供了stoplocktask就是调用了ams的stoplocktaskmode方法
public boolean onkeylongpress(int keycode, keyevent event) {
if (keycode == keyevent.keycode_back) {
stoplocktask();
}
return false;
}
3.直接在settings中对这项进行置灰处理
在securitysettings会读取security_settings_misc.xml文件然后加入相关perference，这其中就会有如下是屏幕固定相关的
<preferencescreen
android:key="screen_pinning_settings"
android:title="@string/screen_pinning_title"
android:summary="@string/switch_off_text"
android:fragment="com.android.settings.screenpinningsettings"/>
我们可以在securitysettings读取该文件之后，调用wms的hasnavigationbar来看有没有虚拟键（没有虚拟按键到时候不能取消屏幕固定），如果没有直接把settings中这项置灰。
// append the rest of the settings
addpreferencesfromresource(r.xml.security_settings_misc);
iwindowmanager windowmanager = windowmanagerglobal.getwindowmanagerservice();
try {
boolean is_screen_pining = windowmanager.hasnavigationbar();
root.findpreference(key_screen_pinning).setenabled(is_screen_pining);
} catch(remoteexception e) {
log.e("securitysettings", "get window service remoteexception.");
}
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