Reset Combo-box C# WP 8.1

Question

my problem is that i don't know how to reset a combo-box to it's default value choose an item , after clicking a button. I only found the following code, but it erases all the items of tha combo-box which is not what i want!

myCombo1.Items.Clear();

Also, is it possible to create an instance of MainPage and use it in navigation function?

Frame.Navigate(typeof(MainPage));

Answer 1

这应该可以解决问题：

myCombo1.SelectedIndex = -1;

Answer 2

Use simplly clear() method :
ComboBoxName.Clear(); .