Saturday, February 13, 2010

Expandable lists and check boxes

I got another trivial question in a comment: how to add checkboxes to an expandable list view like this one? Nothing can be simpler, you just add CheckBox control to the child view that forms the row and that's it. Except that it does not work without some tweaks.

You can download the example program from here.

The first bizarre thing you can notice in res/layout/child_row.xml that the CheckBox is made non-focusable. Why to do that when we want the checkbox to capture "click" events beside "touch" events? There is a complicated answer already presented in this post. The ViewGroup encapsulating the list row (the LinearLayout in res/layout/child_row.xml) must retain the focus otherwise we don't get onChildClick events (see

This would solve the problem for a Button but not for a CheckBox. Actually, I don't know why the Button behaves correctly and the CheckBox does not. My experience is that even if CheckBox has the focus, clicking on the row of the CheckBox does not toggle its state. I am curious if anyone can provide an explanation, here I just record the fact. Remove the android:focusable="false" line from the CheckBox element in child_row.xml and observe, that you can click on the highlighted row as much as you like but the CheckBox does not toggle. That's why I implemented it by "hand" - I took away the focus from the CheckBox, this makes the child row deliver onChildClick events then I toggled the state of the CheckBox programmatically. If anyone has a better solution, I would be deeply interested.

Update: a discussion started in the comment field regarding the erratic behaviour of check boxes in this example program. See this blog post for further explanation.