Usually, the WPF controls are declared in the .xaml file and not in the code behind (.xaml.cs file). However, we might need to use some of those controls in the code behind in order to manipulate them. How can we get the handle of such a control if it “resides” in the xaml file? Take a look at the following xaml code:

<Window x:Class="WpfApplication2.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300" MouseLeftButtonDown="window_Clicked">
    <Grid>
        <TextBlock x:Name="fullNameControl" FontSize="20"
                   Text="{Binding Path=FullName}">
        </TextBlock>
    </Grid>
</Window>

There is a TextBlock called fullNameControl, in the code behind I change its background color to gold when the window is clicked:

As we all know whenever we build an ASP.NET application with a MasterPage, all the controls receive a prefix such as “ctl00$<ContentPlaceHolderID>$<NameYouGaveToControl>”  to their names according to their place in the page hierarchy. That is done in order to prevent from two controls to have the same ID on the same page.
We encounter a problem [...]