实现自定义view(1)：可在全屏幕自由拖动的view

Android中自带的view种类很多，但是有时候不能满足我们的需求，下面介绍一种自定义view的方法，实现了拖动矩形到屏幕任意位置的需求。

下图为运行效果图：

废话不多说，直接上代码

Activity.java

package com.zhuozhuo;

import android.app.Activity;
import android.os.Bundle;

public class CSDNActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    
    
}

CustomView.java 自定义的view，需要覆盖onDraw()方法绘制控件，覆盖onTouchEvent()接收触摸消息

package com.zhuozhuo;

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
	}

}

main.xml 布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<com.zhuozhuo.CustomView android:layout_width="fill_parent"
    android:layout_height="fill_parent"/>
</LinearLayout>

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