每次单击按钮后如何从位图中删除点

Question

I have a system which places a small dot on my bitmap for each menu option I select. However I only want one dot to appear on my bitmap at one time so when I click a second option another dot will appear. I have a clearPoint method which is used to clear the points off the bitmap, how could I implement it so when i press a new button option the new dot is drawn but the previous is removed instead off all dots being removed.

This is my menu option

@Override
public boolean onMenuItemClick(MenuItem menuItem) {
    switch (menuItem.getItemId()) {
        case R.id.A:
            fmob.mZoomView.setPoint(list.get(0).getLocationY(), list.get(0).getLocationX());
            Toast.makeText(getBaseContext(), "Location A", Toast.LENGTH_SHORT).show();
        return true;
        case R.id.B:
            Toast.makeText(getBaseContext(), "Selected Location B", Toast.LENGTH_SHORT).show();
            fmob.mZoomView.setPoint(list.get(1).getLocationY(), list.get(1).getLocationX());
            return true;
        default:
            return false;
    }
}

This is my clearPoint method

public void clearPoints() {
    points.clear();
    routepoints.clear();
    invalidate();
}

Answer 1

If you already have an event listener, then you should make a method which uses premade methods to first> clear the bitmap, second> add the new point, and third> display the updated bitmap. It has to be done in that order or else a semantical error may occur. I would just have the method structured like this:

public void newPoint(int x, int y) /*throws InvalidPointException*/{
    clearPoints();
    //clear the points on the bitmap

    updateBitmapDisplay();
    //update the bitmap with the new points

    addPoint(x, y);
    //add the point to the bitmap

    updateBitmapDisplay();
    //update the bitmap with new points
}

You would then have to use top-down-programming to make these methods using what is available to you. I don't fully understand your question fully, though, so this may be of no use to you. Sorry if that turns out to be the case and you needed something different.