Cannot Assign x:Name to Elements Inside ContentControl in WPF UserControl

Question

Hello,

I have created a UserControl in WPF that contains a ContentControl. This ContentControl can accept any external content (Grid, StackPanel, TextBox, etc.).

However, when I use the UserControl in another page and try to assign x:Name to elements inside the ContentControl, I get a build error, and the application does not run.

UserControl XAML Code:

<UserControl x:Class="MyNamespace.MyUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid>
        <ContentControl x:Name="MyContentControl"/>
    </Grid>
</UserControl>

Usage in MainWindow.xaml:

<Window x:Class="MyNamespace.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:MyNamespace">
    <Grid>
        <local:MyUserControl>
            <local:MyUserControl.Content>
                <StackPanel>
                    <TextBox x:Name="MyTextBox" Text="Hello" />
                    <Button x:Name="MyButton" Content="Click" />
                </StackPanel>
            </local:MyUserControl.Content>
        </local:MyUserControl>
    </Grid>
</Window>

Error Message (Build Error):

XAML error: The name 'MyTextBox' is already used by an existing element.

XAML error: Cannot set Name attribute value 'MyButton' on element 'Button'. 'MyButton' is already used by an existing element.

Build failed.

I am getting this error at compile time, and the application does not run at all.

How can I solve this issue? How can I use x:Name for elements inside a ContentControl when providing external content?

Thanks!

Answer 1

Hi, @fatih uyanık. Welcome to Microsoft Q&A. 

Solution 1: Use a normal Class instead of UserControl with xaml

Create a normal Class file and let it inherit UserControl.

    public class MyUserControl:UserControl
    {
        protected override void OnInitialized(EventArgs e)
        {
            base.OnInitialized(e);

            Grid grid = new Grid();

            ContentControl content = new ContentControl();
            content.Name = "MyContentControl";
            grid.Children.Add(content);

        }
    }

Use MyUserControl in MainWindow.xaml.

    <Grid>
        <local: MyUserControl >
            <StackPanel>
                <TextBox x:Name="MyTextBox" Text="Hello" />
                <Button x:Name="MyButton" Content="Click" />
            </StackPanel>
        </local: MyUserControl >
    </Grid>

Solution 2: Use CustomControl instead of UserControl

Create CustomControl and let it inherit ContentControl.

public class MyCustomControl : ContentControl
{
    static MyCustomControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MyCustomControl), new FrameworkPropertyMetadata(typeof(MyCustomControl)));
    }
}

Edit the corresponding Generic.xaml file.

    <Style TargetType="{x:Type local:MyCustomControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:MyCustomControl}">
                    <Grid>
                        <ContentControl Content="{TemplateBinding Content}"/>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

Use MyCustomControl in MainWindow.xaml.

    <Grid>
        <local:MyCustomControl>
            <StackPanel>
                <TextBox x:Name="MyTextBox" Text="Hello" />
                <Button x:Name="MyButton" Content="Click" />
            </StackPanel>
        </local:MyCustomControl>
    </Grid>

For more detailed solutions, please refer to the document:Document Links

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