UISlider event listener missing for foreground sprite

[Arcanor]

I've created a UISlider with background, foreground and thumb sprites.  All three of them have Box Colliders.  When I hit Play, I can drag the thumb and it responds, I can click or drag in the background area (the black area on the right) and it responds, but when I click or drag on the foreground area of the slider (the blue area to the left) it doesn't respond.


I noticed in the Inspector that my thumb and background sprite gameobjects are having UIEventListener.Get() called on them, but the foreground sprite isn't getting any event listener added.  Here is what I think is the relevant code in UISlider.cs:

1.    protected override void OnStart ()
2.    {
3.       GameObject bg = (mBG != null && mBG.collider != null) ? mBG.gameObject : gameObject;
4.       UIEventListener bgl = UIEventListener.Get(bg);
5.       bgl.onPress += OnPressBackground;
6.       bgl.onDrag += OnDragBackground;
7.  
8.       if (thumb != null && thumb.collider != null && (mFG == null || thumb != mFG.cachedTransform))
9.       {
10.          UIEventListener fgl = UIEventListener.Get(thumb.gameObject);
11.          fgl.onPress += OnPressForeground;
12.          fgl.onDrag += OnDragForeground;
13.       }
14.    }
15.  

Why isn't the foreground sprite registering to receive events?

Thanks in advance!

[ArenMook]

Remove the box collider from the foreground image.

[Arcanor]

Thanks, that's fixed it.  It's a little unintuitive, but I understand why it's done this way.