使用雙緩衝技術實現Android畫板應用

什麼是雙緩衝技術？雙緩衝技術就是當使用者操作介面完成後，會有一個緩衝區儲存使用者操作的結果。

為什麼要使用雙緩衝技術？拿Android 遊戲開發來說，介面貞每次都是全部重畫的，也就說畫了新的，舊的就沒了，所以需要使用雙緩衝技術儲存之前的內容。

如何?雙緩衝？使用一個Bitmap對象保留之前的畫布即可。

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);}@Overridepublic 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;}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);Paint bmpPaint = new Paint();canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);canvas.drawPath(path, paint);}}