使用双缓冲技术实现Android画板应用

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);   }    }