7.2.3 采用双缓冲实现画图板

package com.example.test33;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Bitmap.Config;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class DrawView extends View {
    Paint paint;
    Canvas cacheCanvas;
    Bitmap cacheBitmap;
    Path path;

    public DrawView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub
        this.initDrawView();
    }

    public DrawView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub
        this.initDrawView();
    }

    public DrawView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // TODO Auto-generated constructor stub
        this.initDrawView();
    }
    
    private void initDrawView(){
        cacheBitmap = Bitmap.createBitmap(720, 1280, Config.ARGB_8888);
        cacheCanvas = new Canvas(cacheBitmap);
        paint = new Paint(Paint.DITHER_FLAG);
        paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(1);
        // 反锯齿
        paint.setAntiAlias(true);
        paint.setDither(true);
        path = new Path();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        // TODO Auto-generated method stub
        super.onDraw(canvas);
        canvas.drawBitmap(cacheBitmap, 0, 0, paint);
        canvas.drawPath(path, paint);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub
        float x = event.getX();
        float y = event.getY();
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            path.moveTo(x, y);
            break;
        case MotionEvent.ACTION_MOVE:
            path.lineTo(x, y);
            break;
        case MotionEvent.ACTION_UP:
            cacheCanvas.drawPath(path, paint);
            path.reset();
            break;
        default:
            break;
        }
        this.invalidate();
        return true;
    }

}

 1级缓冲是将一次按下拖动抬起手指的绘画动作存储在path中, 动作结束后绘制到屏幕, 2级缓冲是利用绑定了bitmap的画布将历史数据都保存进去.