I want to bind from UserControl to DataTemplate.

But I get error

Cannot find source for binding with reference 'ElementName=LoginTextBox'. BindingExpression:(no path); DataItem=null; target element is 'Grid' (Name=''); target property is 'FocusedElement' (type 'IInputElement')

My code

<UserControl>
    <UserControl.Resources>
        
        <DataTemplate DataType="{x:Type models:LocalAuthenticationMethod}">
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="72"/>
                    <ColumnDefinition Width="*"/>
                </Grid.ColumnDefinitions>
                <TextBlock Grid.Column="0" VerticalAlignment="Center"
                       Text="{uiCommon:LocalizationBinding ResourceName=Login}"
                       FontSize="{DynamicResource LoginWindowPropertiesFontSize}"/>
                
                <!-- bind to here -->
                <ComboBox x:Name="LoginTextBox"
                      Grid.Column="1"
                      Height="24"
                      Text="{Binding ElementName=Root, Path=DataContext.Login, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged, NotifyOnTargetUpdated=True}"
                      ItemsSource="{Binding ElementName=Root, Path=DataContext.AvailableUsers, Mode=OneWay}"
                      IsEditable="True"
                      behavior:FocusAdvancement.AdvancesByEnterKey="True"
                      FontSize="{DynamicResource LoginWindowPropertiesFontSize}">
                    <b:Interaction.Behaviors>
                        <behavior:SelectTextOnGotFocusBehavior/>
                        <behavior:SelectTextOnTargetUpdatedBehavior/>
                    </b:Interaction.Behaviors>
                </ComboBox>
            </Grid>
        </DataTemplate>
    </UserControl.Resources>
    <Grid x:Name="Root">

        <!-- how to bind here? -->
        <Grid FocusManager.FocusedElement="{Binding ElementName=LoginTextBox}"> 
            <ContentControl>
                <ContentPresenter Content="{Binding SelectedAuthenticationMethod, Mode=OneWay}"/>
            </ContentControl>
        </Grid>
    </Grid>
</UserControl>

I want to bind FocusedElement to ElementName=LoginTextBox. How can I do it? Is it possible at all?

CodePudding user response：

Is it possible at all?

No, because the name "LoginTextBox" is only available inside the DataTemplate where the ComboBox is defined.

The Grid resides in a different XAML namescope that doesn't know anything about the individual elements that defines the visual appearance of a LocalAuthenticationMethod object.