Question

I am making a Custom Layout Android component by extending abstract class ViewGroup (as per this video tutorial by Romain Guy on Parleys.com : http://www.parleys.com/#st=5&id=2191&sl=1).

My component should contain children, but I want to restrain that to only 1 child, of type ViewGroup as well (such as another LinearLayout or a RelativeLayout). Kindof like the ScrollView. Is there a way to add that restriction?

EDIT:
Final solution as android developer said, is to programatically check the constraints onFinishInflate of the ViewGroup subclass as such:

@Override
public void onFinishInflate()
{
    if (getChildCount() > 1)
        throw new IllegalArgumentException("Only 1 child allowed");

    if (getChildCount() == 0 || !(getChildAt(0) instanceof ViewGroup))
        throw new IllegalArgumentException("Child must be a ViewGroup");
}

Answer 1

sure you can .

simply get the child count by using getChildCount() in order to check that there is only a single child.

then, get the only child there is in the viewGroup by using getChildAt(0) .

after this , use reflection on the result and do whatever extra checks you wish to do on its class (for example , use getSuperclass()