How to make a control front of other control in WPF?

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C#

WPF

WPF-Toolkit

iam using textbox and listbox when i type "a" in textbox it shows "a" based words in listbox but down that list box i have other controls too.i made listbox to be visible only when data is binded to it from database .but the problem is its size is getting increased.i want to show it above the controls .is it possible using wpf.

What I have tried:

<wrappanel panel.zindex=1>
<textbox name=z width=20>
<listbox width=20 visibility=hidden>
<textbox name=x width=20>




when i enter letter in textbox it binds data to listbox and makes listbox to be visible.and its getting extended means its size .this leading textbox named as x also going down .i want to make this listbox to be front of x textbox .i dont want to get it extended.

if anyones know this ,can you please help me over this issue