Android采用双缓冲技术实现画板

package com.lidong.android_ibrary.view;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Path;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;/***@类名 : DrawView*@描述 : 使用双缓存技术实现绘制*@时间 : 2016/4/26 9:18*@作者: 李东*@邮箱 : lidong@chni.com.cn*@company: chni*/public class DrawView extends View { float preX; float preY; private Path path; private Paint paint = null; private int VIEW_WIDTH = 800; private int VIEW_HEIGHT = 600; //定义一个内存中图片，将他作为缓冲区 Bitmap cacheBitmap = null; //定义缓冲区Cache的Canvas对象 Canvas cacheCanvas = null; public DrawView(Context context) {  this(context,null); } public DrawView(Context context, AttributeSet attrs) {  super(context, attrs);  //创建一个与该VIew相同大小的缓冲区  cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH,VIEW_HEIGHT,Bitmap.Config.ARGB_8888);  //创建缓冲区Cache的Canvas对象  cacheCanvas = new Canvas();  path = new Path();  //设置cacheCanvas将会绘制到内存的bitmap上  cacheCanvas.setBitmap(cacheBitmap);  paint = new Paint();  paint.setColor(Color.RED);  paint.setFlags(Paint.DITHER_FLAG);  paint.setStyle(Paint.Style.STROKE);  paint.setStrokeWidth(5);  paint.setAntiAlias(true);  paint.setDither(true); } @Override protected void onDraw(Canvas canvas) {  Paint p = new Paint();  //将cacheBitmap绘制到该View  canvas.drawBitmap(cacheBitmap,0,0,p);  canvas.drawPath(path,paint); } @Override public boolean onTouchEvent(MotionEvent event) {  //获取拖动时间的发生位置   float x = event.getX();   float y = event.getY();  switch (event.getAction()){   case MotionEvent.ACTION_DOWN:    path.moveTo(x,y);    preX = x;    preY = y;    break;   case MotionEvent.ACTION_MOVE:    path.quadTo(preX,preY,x,y);    preX = x;    preY = y;    break;   case MotionEvent.ACTION_UP:    //这是是调用了cacheBitmap的Canvas在绘制    cacheCanvas.drawPath(path,paint);    path.reset();    break;  }  invalidate();//在UI线程刷新VIew  return true; }}