Android画板，橡皮擦为黑色痕迹的问题

本人小菜鸟一枚，最近想做画板（用的疯狂Android讲义中，双缓冲技术那种），遇到一个橡皮擦为黑色痕迹的问题，网上搜索资料，基础太差，实在看不懂，于是写下自己的解决办法，帮助跟我同样的小白。

1.画线改用画圆

问题2.改用画圆后出现，手松开后，橡皮擦效果才显示出来？

     解决：在onTouchEvent 的MotionEvent.ACTION_MOVE中，每次都将写到内存中区canvas.drawPath(path, paint); ----------- -----就是每次移动时，都加上与手松开时调用的方法

第一次发，废话有点多，好吧，上代码（代码太烂，轻喷）

 

 

 

public class DrawView extends View{


	float preX;
	float preY;
	private Bitmap cacheBitmap = null;
	//画布
	Canvas canvas = null;
	//画笔
	public Paint paint = null;
	
	private Path path = null;
	//屏幕宽度  
	private int width;
	//屏幕高度 
	private int height;
	
	public boolean isRubber = false;
	
	public DrawView(Context context, AttributeSet set) {
		super(context,set);
		WindowManager wm = (WindowManager) getContext().getSystemService(
				Context.WINDOW_SERVICE);
		width = wm.getDefaultDisplay().getWidth();
		height = wm.getDefaultDisplay().getHeight();
		cacheBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
		canvas =  new Canvas();
		canvas.drawColor(Color.TRANSPARENT);
		path = new Path();
		//给画布设置bitmap
		canvas.setBitmap(cacheBitmap);
		//初始化画笔信息
		setPaint(Color.BLACK,Params.initStrokeWidth); 
	}


	public void setPaint(int color){
		isRubber = false;
		setPaint(color,5);
	}
	//初始化画笔信息
	public void setPaint(int color,int strokeWidth){
		System.out.println("===========setPaint==========");
		paint = new Paint(Paint.DITHER_FLAG);
		paint.setColor(color);
		// 设置画笔风格
		paint.setStyle(Paint.Style.STROKE);
		paint.setStrokeWidth(strokeWidth);
		// 反锯齿
		paint.setAntiAlias(true);
		paint.setDither(true);
	}
	
	//初始化画笔信息
	public void setRubber(){
		isRubber = true;
		paint = new Paint(Paint.DITHER_FLAG);
		// 设置画笔风格
		paint.setStyle(Paint.Style.STROKE);
		paint.setStrokeWidth(Params.initStrokeWidth + 5);
		// 反锯齿
		paint.setAntiAlias(true);
		paint.setDither(true);
		paint.setXfermode(new PorterDuffXfermode(Mode.DST_OUT));
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		float x  = event.getX();
		float y  = event.getY();
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			System.out.println("====MotionEvent.ACTION_DOWN===DOWN");
			path.moveTo(x, y);
			preX = x;
			preY = y;
			break;
		case MotionEvent.ACTION_MOVE:
			System.out.println("====MotionEvent.ACTION_MOVE:===MOVE");
			path.quadTo(preX, preY, x, y);
			preX = x;
			preY = y;
			if(isRubber){
				//这样性能可能会很差，自己想办法解决
				canvas.drawPath(path, paint); // 橡皮擦关键点================== 看这里 问题2解决============
			}
			break;
		case MotionEvent.ACTION_UP:
			System.out.println("====MotionEvent.ACTION_UP===UP");
			canvas.drawPath(path, paint); //用画笔和路径画一张图片
			path.reset(); //重置路径
			break;
		}
		invalidate();//重新绘制 onDraw
		return true;
	} 
	
	@Override
	protected void onDraw(Canvas canvas) {
		Paint bmpPaint = new Paint();
		// 将cacheBitmap绘制到该View组件上
		canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);
		
		if (isRubber) {  //橡皮擦走这边  ======================看这里 问题一解决======================
			canvas.drawCircle(preX, preY, 5, paint);
		} else {
			canvas.drawPath(path, paint);
		}
	}
	


}