findViewById() returns null for custom component in layout XML, not for other components

Question

I have a res/layout/main.xml including these elements and others:

Answer 1

I have the same problem because in my custom view I overrided constructor but invoked super contructor withot attrs paramete. That is copy paste)

My previous constructor version:

    public TabsAndFilterRelativeLayout(Context context, AttributeSet attrs) {
            super(context);
}

Now I have:

    public TabsAndFilterRelativeLayout(Context context, AttributeSet attrs) {
            super(context, attrs);}

And that works!