自定义可移动view

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class CustomView extends View {

private static final int WIDTH = 40;

private Rect rect = new Rect(0, 0, WIDTH, WIDTH);//绘制矩形的区域
private int deltaX,deltaY;//点击位置和图形边界的偏移量
private static Paint paint = new Paint();//画笔

public CustomView(Context context, AttributeSet attrs) {
super(context, attrs);
paint = new Paint();
paint.setColor(Color.RED);//填充红色
}

@Override
protected void onDraw(Canvas canvas) {
canvas.drawRect(rect, paint);//画矩形

}

@Override
public boolean onTouchEvent (MotionEvent event) {
int x = (int) event.getX();
int y = (int) event.getY();
switch(event.getAction()) {
case MotionEvent.ACTION_DOWN:
if(!rect.contains(x, y)) {
return false;//没有在矩形上点击，不处理触摸消息
}
deltaX = x - rect.left;
deltaY = y - rect.top;
break;
case MotionEvent.ACTION_MOVE:
case MotionEvent.ACTION_UP:
Rect old = new Rect(rect);
//更新矩形的位置
rect.left = x - deltaX;
rect.top = y - deltaY;
rect.right = rect.left + WIDTH;
rect.bottom = rect.top + WIDTH;
old.union(rect);//要刷新的区域，求新矩形区域与旧矩形区域的并集
invalidate(old);//出于效率考虑，设定脏区域，只进行局部刷新，不是刷新整个view
break;
}
return true;//处理了触摸消息，消息不再传递
}

}