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);

}

}

}