雙緩沖技術實現Android 畫板應用

什麼是雙緩沖技術？雙緩沖技術就是當用戶操作界面完成後，會有一個緩沖區保存用戶操作的結果。

為什麼要使用雙緩沖技術？拿Android 游戲開發來說，界面貞每次都是全部重畫的，也就說畫了新的，舊的就沒了，所以需要使用雙緩沖技術保存之前的內容。

如何實現雙緩沖？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); 
 } 
 
 @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); 
 } 
 
} 

以上就是對Android雙緩沖技術實現畫板應用實例，有需要的朋友可以參考下。