Android下圖片或按鈕等可拖動到任意位置的效果實現源碼

Android下圖片可拖動到任意位置的效果
下面為Activity的代碼：

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public class DraftTest extends Activity {
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 /** Called when the activity is first created. */
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 @Override
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 public void onCreate(Bundle savedInstanceState) { 
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  super.onCreate(savedInstanceState); 
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  setContentView(R.layout.sign);
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  DisplayMetrics dm = getResources().getDisplayMetrics();
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  final int screenWidth = dm.widthPixels; 
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  final int screenHeight = dm.heightPixels - 50; 
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  //拖動的按鈕
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  final Button b=(Button)findViewById(R.id.startBtn);
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  //添加觸摸事件
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  b.setOnTouchListener(new OnTouchListener(){
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   int lastX, lastY; //記錄移動的最後的位置
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   public boolean onTouch(View v, MotionEvent event) { 
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    //獲取Action
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    int ea=event.getAction();
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    Log.i("TAG", "Touch:"+ea);
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    switch(ea){ 
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    case MotionEvent.ACTION_DOWN:   //按下
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     lastX = (int) event.getRawX(); 
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     lastY = (int) event.getRawY(); 
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     break; 
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     /**
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      * layout(l,t,r,b)
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      * l  Left position, relative to parent 
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                    t  Top position, relative to parent 
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                    r  Right position, relative to parent 
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                    b  Bottom position, relative to parent  
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      * */
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    case MotionEvent.ACTION_MOVE:  //移動
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     //移動中動態設置位置
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     int dx =(int)event.getRawX() - lastX; 
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     int dy =(int)event.getRawY() - lastY; 
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     int left = v.getLeft() + dx; 
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     int top = v.getTop() + dy; 
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     int right = v.getRight() + dx; 
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     int bottom = v.getBottom() + dy; 
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     if(left < 0){ 
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      left = 0; 
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      right = left + v.getWidth(); 
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     } 
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     if(right > screenWidth){ 
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      right = screenWidth; 
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      left = right - v.getWidth(); 
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     } 
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     if(top < 0){ 
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      top = 0; 
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      bottom = top + v.getHeight(); 
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     } 
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     if(bottom > screenHeight){ 
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      bottom = screenHeight; 
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      top = bottom - v.getHeight(); 
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     } 
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     v.layout(left, top, right, bottom); 
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     Log.i("", "position：" + left +", " + top + ", " + right + ", " + bottom);
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     //將當前的位置再次設置
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     lastX = (int) event.getRawX(); 
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     lastY = (int) event.getRawY(); 
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     break; 
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    case MotionEvent.ACTION_UP:   //脫離
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     break;               
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    } 
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    return false; 
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   }}); 
70     www.2cto.com
 }
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}
XML配置文件Sign.xml的代碼:

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<?xml version="1.0" encoding="utf-8"?>
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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
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 android:id="@+id/layoutRacingNeedForSpeed" android:padding="0px"
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 android:layout_width="fill_parent" android:layout_height="fill_parent">
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 <Button
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  android:id="@+id/startBtn"
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  android:text="tuodongdeanniu"
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  android:layout_centerInParent="true"
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  android:layout_width="wrap_content" android:layout_height="wrap_content"/>
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</RelativeLayout>
作者：Jimmy_牛牛