Android实现图片拖动效果

要求：

1.通过手指移动来拖动图片 

2.控制图片不能超出屏幕显示区域

技术点:

1.MotionEvent处理

2.对View进行动态定位(layout)

activity_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
 android:id="@+id/iv_main"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:src="@drawable/test"/>
</RelativeLayout>

MainActivity:

public class MainActivity extends Activity implements OnTouchListener {
private ImageView iv_main;
private RelativeLayout parentView;
@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 iv_main = (ImageView) findViewById(R.id.iv_main);
 parentView = (RelativeLayout) iv_main.getParent();
 /*
 int right = parentView.getRight(); //0
 int bottom = parentView.getBottom(); //0
 Toast.makeText(this, right+"---"+bottom, 1).show();
 */
 //设置touch监听
 iv_main.setOnTouchListener(this);
}
private int lastX;
private int lastY;
private int maxRight;
private int maxBottom;
@Override
public boolean onTouch(View v, MotionEvent event) {
 //得到事件的坐标
 int eventX = (int) event.getRawX();
 int eventY = (int) event.getRawY();
 switch (event.getAction()) {
 case MotionEvent.ACTION_DOWN:
  //得到父视图的right/bottom
  if(maxRight==0) {//保证只赋一次值
   maxRight = parentView.getRight();
   maxBottom = parentView.getBottom();
  }
  //第一次记录lastX/lastY
  lastX =eventX;
  lastY = eventY;
  break;
 case MotionEvent.ACTION_MOVE:
  //计算事件的偏移
  int dx = eventX-lastX;
  int dy = eventY-lastY;
  //根据事件的偏移来移动imageView
  int left = iv_main.getLeft()+dx;
  int top = iv_main.getTop()+dy;
  int right = iv_main.getRight()+dx;
  int bottom = iv_main.getBottom()+dy;
  //限制left >=0
  if(left<0) {
   right += -left;
   left = 0;
  }
  //限制top
  if(top<0) {
   bottom += -top;
   top = 0;
  }
  //限制right <=maxRight
  if(right>maxRight) {
   left -= right-maxRight;
   right = maxRight;
  }
  //限制bottom <=maxBottom
  if(bottom>maxBottom) {
   top -= bottom-maxBottom;
   bottom = maxBottom;
  }
  iv_main.layout(left, top, right, bottom);
  //再次记录lastX/lastY
  lastX = eventX;
  lastY = eventY;
  break;
 default:
  break;
 }
 return true;//所有的motionEvent都交给imageView处理
}
}

来源：http://www.cnblogs.com/ganchuanpu/p/6512195.html