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.