Android: ClassCastException when adding a header view to ExpandableListView

Question

I'm trying to add a header to an ExpandableListView like so:

headerView = View.inflate(this, R.layout.header, null);
expandableListView.addHeaderView(headerView);
expandableListView.setAdapter(new SectionedAdapter(this));

Which gives me the following error:

 12-08 16:23:42.354:
 ERROR/AndroidRuntime(421): Caused by:java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams
 12-08 16:23:42.354:   ERROR/AndroidRuntime(421): at android.widget.ListView.clearRecycledState(ListView.java:504)
 12-08 16:23:42.354: ERROR/AndroidRuntime(421): at android.widget.ListView.resetList(ListView.java:490)
 12-08 16:23:42.354:ERROR/AndroidRuntime(421):at android.widget.ListView.setAdapter(ListView.java:422)
 12-08 16:23:42.354:ERROR/AndroidRuntime(421): at android.widget.ExpandableListView.setAdapter(ExpandableListView.java:475)

This is happening at the call to expandableListView.setAdapter(new SectionedAdapter(this)), but I can't figure out why. Any ideas?

Answer 1

Ok, I figured this one out. I got rid of the runtime error by programatically setting the View's LayoutParams to ListView LayoutParams, like so:

headerView.setLayoutParams(new ListView.LayoutParams(ListView.LayoutParams.FILL_PARENT, ListView.LayoutParams.WRAP_CONTENT));

before adding the view. The reason being is found in the Android docs:

http://developer.android.com/reference/android/view/View.html#setLayoutParams(android.view.ViewGroup.LayoutParams)

which states that:

These supply parameters to the parent of this view specifying how it should be arranged. There are many subclasses of ViewGroup.LayoutParams, and these correspond to the different subclasses of ViewGroup that are responsible for arranging their children.

So basically, if you are adding a view to another, you MUST set the LayoutParams of the view to the LayoutParams type that the parent uses, or you will get a runtime error.