什么是双缓冲技术？双缓冲技术就是当用户操作界面完成后，会有一个缓冲区保存用户操作的结果。
为什么要使用双缓冲技术？拿Android 游戏开发来说，界面贞每次都是全部重画的，也就说画了新的，旧的就没了，所以需要使用双缓冲技术保存之前的内容。
如何实现双缓冲？使用一个Bitmap对象保留之前的画布即可。
package com.example.phonegaptest;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Bitmap.Config;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;public class DrawView extends View { float preX; float preY; private Path path; public Paint paint = null; final int VIEW_WIDTH = 320; final int VIEW_HEIGHT = 480; Bitmap cacheBitmap = null; Canvas cacheCanvas = null; public DrawView(Context context, AttributeSet set) { super(context, set); cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT, Config.ARGB_8888); cacheCanvas = new Canvas(); path = new Path(); cacheCanvas.setBitmap(cacheBitmap); paint = new Paint(Paint.DITHER_FLAG); paint.setColor(Color.RED); paint.setStyle(Paint.Style.STROKE); paint.setStrokeWidth(1); paint.setAntiAlias(true); paint.setDither(true); } @Override public boolean onTouchEvent(MotionEvent event) { 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: cacheCanvas.drawPath(path, paint); path.reset(); break; } invalidate(); return true; } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Paint bmpPaint = new Paint(); canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint); canvas.drawPath(path, paint); }}