System.Windows.Controls Radio button and Combo Box

Hi All

I have a treeview, Radio buttons and combo box in window with default selection for Radio button and combo box.

Treeview should load based on radio button checked and combo box selection so I am checking combo box selection in radio button checked event and checking combo box selection in radio button checked event .

The Problem I am facing here is

in Initialization radio button checked event combobox is NULL or in combo box selection event radio button is null.

Pleaase help me I am new to WPF.

Thanks in Advance