Android PickerView滚动选择器的使用方法

手机里设置闹钟需要选择时间，那个选择时间的控件就是滚动选择器，前几天用手机刷了miui，发现自带的那个时间选择器效果挺好看的，于是就自己仿写了一个，权当练手。先来看效果：

                                                                

效果还行吧？实现思路就是自定义一个pickerview，单独滚动的是一个pickerview，显然上图中有分和秒的选择所以在布局里用了两个pickerview。由于这里不涉及到text的点击事件，所以只需要继承view就行了，直接把text用canvas画上去。pickerview的实现的主要难点：

难点1：

        字体随距离的渐变。可以看到，text随离中心位置的距离变化而变化，这里变化的是透明度alpha和字体大小texsize，这两个值我都设置了max和min值，通过其与中心点的距离计算scale。我用的是变化曲线是抛物线scale=1-ax^2(x<=height/4),scale = 0(x>height/4)，a=(4/height)^2。x就是距离view中心的偏移量。用图片表示如下：

难点2：

     text的居中。绘制text的时候不仅要使其在x方向上居中，还要在y方向上居中，在x方向上比较简单，设置paint的align为align.center就行了，但是y方向上很蛋疼，需要计算text的baseline。

难点3：

    循环滚动。为了解决循环滚动的问题我把存放text的list从中间往上下摊开，通过不断地moveheadtotail和movetailtohead使选中的text始终是list的中间position的值。

 以上就是几个难点，了解了之后可以来看pickerview的代码了：

package com.jingchen.timerpicker; 
 
import java.util.arraylist; 
import java.util.list; 
import java.util.timer; 
import java.util.timertask; 
 
import android.content.context; 
import android.graphics.canvas; 
import android.graphics.paint; 
import android.graphics.paint.align; 
import android.graphics.paint.fontmetricsint; 
import android.graphics.paint.style; 
import android.os.handler; 
import android.os.message; 
import android.util.attributeset; 
import android.view.motionevent; 
import android.view.view; 
 
/** 
 * 滚动选择器 
 * 
 * @author chenjing 
 * 
 */ 
public class pickerview extends view 
{ 
 
  public static final string tag = "pickerview"; 
  /** 
   * text之间间距和mintextsize之比 
   */ 
  public static final float margin_alpha = 2.8f; 
  /** 
   * 自动回滚到中间的速度 
   */ 
  public static final float speed = 2; 
 
  private list<string> mdatalist; 
  /** 
   * 选中的位置，这个位置是mdatalist的中心位置，一直不变 
   */ 
  private int mcurrentselected; 
  private paint mpaint; 
 
  private float mmaxtextsize = 80; 
  private float mmintextsize = 40; 
 
  private float mmaxtextalpha = 255; 
  private float mmintextalpha = 120; 
 
  private int mcolortext = 0x333333; 
 
  private int mviewheight; 
  private int mviewwidth; 
 
  private float mlastdowny; 
  /** 
   * 滑动的距离 
   */ 
  private float mmovelen = 0; 
  private boolean isinit = false; 
  private onselectlistener mselectlistener; 
  private timer timer; 
  private mytimertask mtask; 
 
  handler updatehandler = new handler() 
  { 
 
    @override 
    public void handlemessage(message msg) 
    { 
      if (math.abs(mmovelen) < speed) 
      { 
        mmovelen = 0; 
        if (mtask != null) 
        { 
          mtask.cancel(); 
          mtask = null; 
          performselect(); 
        } 
      } else 
        // 这里mmovelen / math.abs(mmovelen)是为了保有mmovelen的正负号，以实现上滚或下滚 
        mmovelen = mmovelen - mmovelen / math.abs(mmovelen) * speed; 
      invalidate(); 
    } 
 
  }; 
 
  public pickerview(context context) 
  { 
    super(context); 
    init(); 
  } 
 
  public pickerview(context context, attributeset attrs) 
  { 
    super(context, attrs); 
    init(); 
  } 
 
  public void setonselectlistener(onselectlistener listener) 
  { 
    mselectlistener = listener; 
  } 
 
  private void performselect() 
  { 
    if (mselectlistener != null) 
      mselectlistener.onselect(mdatalist.get(mcurrentselected)); 
  } 
 
  public void setdata(list<string> datas) 
  { 
    mdatalist = datas; 
    mcurrentselected = datas.size() / 2; 
    invalidate(); 
  } 
 
  public void setselected(int selected) 
  { 
    mcurrentselected = selected; 
  } 
 
  private void moveheadtotail() 
  { 
    string head = mdatalist.get(0); 
    mdatalist.remove(0); 
    mdatalist.add(head); 
  } 
 
  private void movetailtohead() 
  { 
    string tail = mdatalist.get(mdatalist.size() - 1); 
    mdatalist.remove(mdatalist.size() - 1); 
    mdatalist.add(0, tail); 
  } 
 
  @override 
  protected void onmeasure(int widthmeasurespec, int heightmeasurespec) 
  { 
    super.onmeasure(widthmeasurespec, heightmeasurespec); 
    mviewheight = getmeasuredheight(); 
    mviewwidth = getmeasuredwidth(); 
    // 按照view的高度计算字体大小 
    mmaxtextsize = mviewheight / 4.0f; 
    mmintextsize = mmaxtextsize / 2f; 
    isinit = true; 
    invalidate(); 
  } 
 
  private void init() 
  { 
    timer = new timer(); 
    mdatalist = new arraylist<string>(); 
    mpaint = new paint(paint.anti_alias_flag); 
    mpaint.setstyle(style.fill); 
    mpaint.settextalign(align.center); 
    mpaint.setcolor(mcolortext); 
  } 
 
  @override 
  protected void ondraw(canvas canvas) 
  { 
    super.ondraw(canvas); 
    // 根据index绘制view 
    if (isinit) 
      drawdata(canvas); 
  } 
 
  private void drawdata(canvas canvas) 
  { 
    // 先绘制选中的text再往上往下绘制其余的text 
    float scale = parabola(mviewheight / 4.0f, mmovelen); 
    float size = (mmaxtextsize - mmintextsize) * scale + mmintextsize; 
    mpaint.settextsize(size); 
    mpaint.setalpha((int) ((mmaxtextalpha - mmintextalpha) * scale + mmintextalpha)); 
    // text居中绘制，注意baseline的计算才能达到居中，y值是text中心坐标 
    float x = (float) (mviewwidth / 2.0); 
    float y = (float) (mviewheight / 2.0 + mmovelen); 
    fontmetricsint fmi = mpaint.getfontmetricsint(); 
    float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0)); 
 
    canvas.drawtext(mdatalist.get(mcurrentselected), x, baseline, mpaint); 
    // 绘制上方data 
    for (int i = 1; (mcurrentselected - i) >= 0; i++) 
    { 
      drawothertext(canvas, i, -1); 
    } 
    // 绘制下方data 
    for (int i = 1; (mcurrentselected + i) < mdatalist.size(); i++) 
    { 
      drawothertext(canvas, i, 1); 
    } 
 
  } 
 
  /** 
   * @param canvas 
   * @param position 
   *      距离mcurrentselected的差值 
   * @param type 
   *      1表示向下绘制，-1表示向上绘制 
   */ 
  private void drawothertext(canvas canvas, int position, int type) 
  { 
    float d = (float) (margin_alpha * mmintextsize * position + type 
        * mmovelen); 
    float scale = parabola(mviewheight / 4.0f, d); 
    float size = (mmaxtextsize - mmintextsize) * scale + mmintextsize; 
    mpaint.settextsize(size); 
    mpaint.setalpha((int) ((mmaxtextalpha - mmintextalpha) * scale + mmintextalpha)); 
    float y = (float) (mviewheight / 2.0 + type * d); 
    fontmetricsint fmi = mpaint.getfontmetricsint(); 
    float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0)); 
    canvas.drawtext(mdatalist.get(mcurrentselected + type * position), 
        (float) (mviewwidth / 2.0), baseline, mpaint); 
  } 
 
  /** 
   * 抛物线 
   * 
   * @param zero 
   *      零点坐标 
   * @param x 
   *      偏移量 
   * @return scale 
   */ 
  private float parabola(float zero, float x) 
  { 
    float f = (float) (1 - math.pow(x / zero, 2)); 
    return f < 0 ? 0 : f; 
  } 
 
  @override 
  public boolean ontouchevent(motionevent event) 
  { 
    switch (event.getactionmasked()) 
    { 
    case motionevent.action_down: 
      dodown(event); 
      break; 
    case motionevent.action_move: 
      domove(event); 
      break; 
    case motionevent.action_up: 
      doup(event); 
      break; 
    } 
    return true; 
  } 
 
  private void dodown(motionevent event) 
  { 
    if (mtask != null) 
    { 
      mtask.cancel(); 
      mtask = null; 
    } 
    mlastdowny = event.gety(); 
  } 
 
  private void domove(motionevent event) 
  { 
 
    mmovelen += (event.gety() - mlastdowny); 
 
    if (mmovelen > margin_alpha * mmintextsize / 2) 
    { 
      // 往下滑超过离开距离 
      movetailtohead(); 
      mmovelen = mmovelen - margin_alpha * mmintextsize; 
    } else if (mmovelen < -margin_alpha * mmintextsize / 2) 
    { 
      // 往上滑超过离开距离 
      moveheadtotail(); 
      mmovelen = mmovelen + margin_alpha * mmintextsize; 
    } 
 
    mlastdowny = event.gety(); 
    invalidate(); 
  } 
 
  private void doup(motionevent event) 
  { 
    // 抬起手后mcurrentselected的位置由当前位置move到中间选中位置 
    if (math.abs(mmovelen) < 0.0001) 
    { 
      mmovelen = 0; 
      return; 
    } 
    if (mtask != null) 
    { 
      mtask.cancel(); 
      mtask = null; 
    } 
    mtask = new mytimertask(updatehandler); 
    timer.schedule(mtask, 0, 10); 
  } 
 
  class mytimertask extends timertask 
  { 
    handler handler; 
 
    public mytimertask(handler handler) 
    { 
      this.handler = handler; 
    } 
 
    @override 
    public void run() 
    { 
      handler.sendmessage(handler.obtainmessage()); 
    } 
 
  } 
 
  public interface onselectlistener 
  { 
    void onselect(string text); 
  } 
} 

代码里的注释都写的很清楚了。接下来，我们就用写好的pickerview实现文章开头的图片效果吧~
首先看mainactivity的布局：

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:background="#000000" > 
 
  <relativelayout 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_centerinparent="true" 
    android:background="#ffffff" > 
 
    <com.jingchen.timerpicker.pickerview 
      android:id="@+id/minute_pv" 
      android:layout_width="80dp" 
      android:layout_height="160dp" /> 
 
    <textview 
      android:id="@+id/minute_tv" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_centervertical="true" 
      android:layout_torightof="@id/minute_pv" 
      android:text="分" 
      android:textcolor="#ffaa33" 
      android:textsize="26sp" 
      android:textstyle="bold" /> 
 
    <com.jingchen.timerpicker.pickerview 
      android:id="@+id/second_pv" 
      android:layout_width="80dp" 
      android:layout_height="160dp" 
      android:layout_torightof="@id/minute_tv" /> 
 
    <textview 
      android:id="@+id/second_tv" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_centervertical="true" 
      android:layout_torightof="@id/second_pv" 
      android:text="秒" 
      android:textcolor="#ffaa33" 
      android:textsize="26sp" 
      android:textstyle="bold" /> 
  </relativelayout> 
 
</relativelayout> 

两个pickerview两个textview，很简单。
下面是mainactivity的代码：

package com.jingchen.timerpicker; 
 
import java.util.arraylist; 
import java.util.list; 
 
import com.jingchen.timerpicker.pickerview.onselectlistener; 
 
import android.app.activity; 
import android.os.bundle; 
import android.view.menu; 
import android.widget.textview; 
import android.widget.toast; 
 
public class mainactivity extends activity 
{ 
 
  pickerview minute_pv; 
  pickerview second_pv; 
 
  @override 
  protected void oncreate(bundle savedinstancestate) 
  { 
    super.oncreate(savedinstancestate); 
    setcontentview(r.layout.activity_main); 
    minute_pv = (pickerview) findviewbyid(r.id.minute_pv); 
    second_pv = (pickerview) findviewbyid(r.id.second_pv); 
    list<string> data = new arraylist<string>(); 
    list<string> seconds = new arraylist<string>(); 
    for (int i = 0; i < 10; i++) 
    { 
      data.add("0" + i); 
    } 
    for (int i = 0; i < 60; i++) 
    { 
      seconds.add(i < 10 ? "0" + i : "" + i); 
    } 
    minute_pv.setdata(data); 
    minute_pv.setonselectlistener(new onselectlistener() 
    { 
 
      @override 
      public void onselect(string text) 
      { 
        toast.maketext(mainactivity.this, "选择了 " + text + " 分", 
            toast.length_short).show(); 
      } 
    }); 
    second_pv.setdata(seconds); 
    second_pv.setonselectlistener(new onselectlistener() 
    { 
 
      @override 
      public void onselect(string text) 
      { 
        toast.maketext(mainactivity.this, "选择了 " + text + " 秒", 
            toast.length_short).show(); 
      } 
    }); 
  } 
 
  @override 
  public boolean oncreateoptionsmenu(menu menu) 
  { 
    getmenuinflater().inflate(r.menu.main, menu); 
    return true; 
  } 
 
} 

ok了，自定义自己的timerpicker就是这么简单

源码下载：pickerview滚动选择器

希望本文对大家学习滚动选择器pickerview有所帮助。