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;
 }
}