Question

I’m working on an app that involves and ExpandableListView. We should like to replace the groupIndicator with one of our own choosing.

I created a spec for the indicator that would show a different png depending on the state of the selector (expanded or not expanded)

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/arrow_down" android:state_expanded="true"/>
    <item android:drawable="@drawable/arrow_right"/>    
</selector>

I then set up my layout xml to use:

(Note that childDivider is a one pixel tall png rather than a color because setting that to a color seems to be bugged)

This works, except that our icon is stretched out vertically. That makes sense, because we just created a 25×25 icon and hoped for the best. I’m trying to figure out the dimensions of the native icon so that I can match it, but that’s where I run into trouble.

Digging through the source code (ExpandableListView.java) I found that, by default, the class will use com.android.internal.R.styleable.ExpandableListView_groupIndicator. So I have an id, but no icon yet.

I’d love to be able to do:

Bitmap image = BitmapFactory.decodeResource(this.getResources(), com.android.internal.R.styleable.ExpandableListView_groupIndicator);
        imWidth = image.getWidth();
        imHeight = image.getHeight();

But as the “internal” suggests, it’s not visible to me in user space.

I also found getIndicate() in ExpandableListView.java, but it is private, so I can’t get to that either.

I’m quite new to diving into the platform source code, and I don’t know how else to track down that image. Can anyone help me out?

Edit: Thanks CommonsWare. To spell out the rest for anyone else looking:

android:drawable/expander_group is defined in /frameworks/base/core/res/res/drawable/expander_group.xml.
expander_group.xml mentions that it uses @drawable/expander_ic_maximized and @drawable/expander_ic_minimized.
Those drawables can be found in /frameworks/base/core/res/res/drawable/expander_ic_maximized.9.png and /frameworks/base/core/res/res/drawable/expander_ic_minimized.9.png, among other places for specific densities and such. The “9” explains why the default icons don’t have distortion problems – they’re patch-9 graphics. The density-agnostic versions of the icons are 34px by 38px.

Answer 1

base.git‘s core/res/res/values/styles.xml defines com.android.internal.R.styleable.ExpandableListView_groupIndicator as android:drawable/expander_group. That is a StateListDrawable in your SDK’s copy of the resources. The underlying PNGs are of varying sizes based upon density.