Implementing An Eraser In An Android Drawing App - Black Trail And Then Transparent

I have an drawing app for Android and I am currently trying to add a real eraser to it. Before, I had just used white paint for an eraser, but that won't do anymore since now I all

Solution 1:

I could suggest you to read the official sample of FingerPaint.java It exactly matches what you are trying to achieve here.

To not show the trail when you erase content, take a look at the onDraw() method and the eraserMode variable:

@OverrideprotectedvoidonDraw(Canvas canvas) {
    canvas.drawColor(0xFFAAAAAA);
    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
    if (!eraserMode) {
        canvas.drawPath(mPath, mPaint);
    }
}

boolean eraserMode = false;

@OverridepublicbooleanonOptionsItemSelected(MenuItem item) {
    eraserMode = false;
    mPaint.setXfermode(null);
    mPaint.setAlpha(0xFF);
    switch (item.getItemId()) {
        /*...*/caseERASE_MENU_ID:
            // Add this line
            eraserMode = true;
            mPaint.setXfermode(newPorterDuffXfermode(PorterDuff.Mode.CLEAR));
            returntrue;
        /*...*/
    }
    returnsuper.onOptionsItemSelected(item);
}

Solution 2:

People Still looking for a shorter way to remove that black line while erasing. Just addsetLayerType(View.LAYER_TYPE_SOFTWARE, drawPaint); this line to the constructor and here you go. Cheers!

Solution 3:

None of the above answers, worked properly for me. After some hit and trial, and some logics as well, solved it, check the ACTION_MOVE

@Override
public boolean onTouchEvent(MotionEvent event) {

    float touchX = event.getX();
    float touchY = event.getY();

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            isEdited = true;
            drawPath.moveTo(touchX, touchY);
            break;
        case MotionEvent.ACTION_MOVE:
            if(isEraser) {
                drawPath.lineTo(touchX, touchY);
                drawCanvas.drawPath(drawPath, drawPaint);
                drawPath.reset();
                drawPath.moveTo(touchX, touchY);
            } else {
                drawPath.lineTo(touchX, touchY);
            }
            break;
        case MotionEvent.ACTION_UP:
            drawCanvas.drawPath(drawPath, drawPaint);
            drawPath.reset();
            break;
        default:
            returnfalse;
    }

    invalidate();
    returntrue;
}

and this

publicvoidsetEraser(boolean isEraser) {
    this.isEraser = isEraser;
    if (isEraser) {
        drawPaint.setXfermode(newPorterDuffXfermode(PorterDuff.Mode.CLEAR));
    } else {
        drawPaint.setXfermode(null);
    }
}

Solution 4:

Can you comment canvas.drawPath(mPreviewPath, mPaint) line and see if it works:

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawColor(Color.TRANSPARENT);
    canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
    canvas.drawPath(mPath, mPaint);
    //canvas.drawPath(mPreviewPath, mPaint);
}

Solution 5:

when you want make eraser set painting color same as color of canvas not transparent in real life. in android we set set paint color as theme color of canvas mostly either white or black.

mColor = Color.BLACK;
mPaint.setColor(Color.BLACK);
mPaint.setStrokeWidth(mBrushSize);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setAntiAlias(true);