Question

I have two views in a RelativeLayout, both of which fill the screen, so view B is on top of view A. I also have an animation defined which can move view B partially offscreen to show view A underneath. The animation works fine, but I’m having the classic issue of the view bounds not moving with the view, so the button that I use to trigger the animation (which is located on view B) is only clickable from its original position, no matter where view B is located. The issue that I’m having is that after the animation ends, when I set the layout params it’s causing view B to be redrawn again, translated from the location of the end of the animation.

As a concrete example, the left edge of view B is initially at x = 0, with a button at x = 450. When the button is pressed, an animation moves the view to x = -400. This works properly – the view is partially off the left hand side of the screen, and the button is now at x = 50, so it is still on screen. The click area for the button though is still at x = 450. So now I set the layout params on view B:

RelativeLayout.LayoutParams lp = (RelativeLayout.LayoutParams) viewB.getLayoutParams();
lp.rightMargin = 400;
viewB.setLayoutParams(lp);

Once the new params are set, the view gets 400px of padding on the right, moving the entire view to x = -800. The clickable area for the button is now properly at x = 50 though, so it seems like I can have it look right or act right. Any idea what I’m doing wrong? Here’s how the animation is set up.

Animation anim = null;
anim = new TranslateAnimation(0, -400, 0, 0);
anim.setAnimationListener(this);
anim.setDuration(duration);
viewB.startAnimation(anim); 

Answer 1

I was able to get things working by changing the layout params before or after the animation, as appropriate:

private int marginOffsets;

public void triggerAnimation(boolean show, offset)
{
    int curX = 0;
    int newX = 0;
    Animation anim = null;

    this.showingPanel = show;
    if(show)
    {
        curX = 0 - offset;

        android.widget.RelativeLayout.LayoutParams lp = new android.widget.RelativeLayout.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,  ViewGroup.LayoutParams.FILL_PARENT);
        lp.rightMargin = 0;
        rootPanel.setLayoutParams(lp);
    }
    else
    {
        newX = 0 - offset;
    }

    marginOffsets = newX < 0 ? 0 - offset : offset;

    anim = new TranslateAnimation(curX, newX, 0, 0);
    anim.setAnimationListener(this);
    anim.setDuration(duration);
    startAnimation(anim);        
}

public void onAnimationEnd(Animation anim)
{
    //This prevents flicker when the view is moving onscreen.
    clearAnimation();

    if(!showingPanel)
    {
        //Move the margin to move the actual bounds so click events still work.
        RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.FILL_PARENT,  ViewGroup.LayoutParams.FILL_PARENT);
        lp.rightMargin = 0 - marginOffsets;
        rootPanel.setLayoutParams(lp);
    }    
}