How to change default erase color in paint applica

问题:

I make an Application in which I want to erase drawing lines with event. For this I used

mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));

but at the time of erasing a line, that line becomes black first then erased. I want a transparent color for erasing a drawing a path.

回答1:

I have gone through the FingerPaint.java from APIDemos i.e android-sdk\samples\android-17\ApiDemos

and modified

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawColor(0xFFAAAAAA);

    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

    canvas.drawPath(mPath, mPaint);
}

to

@Override
protected void onDraw(Canvas canvas) {
   canvas.drawColor(0xFFAAAAAA);

   canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

   mCanvas.drawPath(mPath, mPaint);  // this line changed 
                                     // mCanvas is Canvas variable which is
                                     // initialized in onSizeChanged()
}

Now it is not drawing a black color while erasing, everything works fine. Not sure it is 100% proper answer but it works for me.

回答2:

Hey I have used a kind of trick to remove the black line.In my erase button, I have set the color to white, instead of using XferMode..

if(erase){
paintColor = Color.parseColor(newColor);
drawPaint.setColor(paintColor);
}

回答3:

The below works for erasing on a transparent background...

Call SetErase(true) to start erasing.

The OnDraw method will then draw a white path (instead of black)which will then get cleared to the transparent color and you keep all your path undo info.

Call SetErase() to toggle erasing on/off

    public void SetErase(bool On)
    {
        if (On)
        {
            if (!_erasing)
            {
                _delpaint = new Paint(_paint);
                _delpaint.Color = Color.White; 
                _paint.SetXfermode(new PorterDuffXfermode(PorterDuff.Mode.Clear));
                _erasing = true;
            }
        }
        else if (_erasing)
        {
            _erasing = false;
            _paint.SetXfermode(null);
        }
    }

    protected override void OnDraw(Canvas canvas)
    {
        canvas.DrawColor(BackgroundColor);
        canvas.DrawBitmap(CanvasBitmap, 0, 0, _bitmapPaint);
        if (_erasing)
        {
            canvas.DrawPath(_path, _delpaint); // draw white path
        }
        else
        {
            canvas.DrawPath(_path, _paint);
        }
    }