wpf binding to element from another xaml file

Question

I am trying to bind some data from the MainWindow to a second file (Type: UserControl ). The second xaml-file should contain the data from a TabItem . I found this answer: wpf : Bind to a control in another xaml file but somehow I am not getting it, maybe because I am new to wpf and xaml.

I made a short example, to show my problem:

MainWindow:

<Window x:Class="BindingBetweenFiles.MainWindow"
...
xmlns:local="clr-namespace:BindingBetweenFiles"
Title="MainWindow" Height="350" Width="525">
<StackPanel>
    <TabControl Height="200">
        <TabItem Header="Tab 1">
            <local:Tab1 />
        </TabItem>
    </TabControl>
    <TextBlock Name="txtblock1">This text should be shown in the tab.</TextBlock>
</StackPanel>
</Window>

Tab1 (Content for TabItem):

<UserControl x:Class="BindingBetweenFiles.Tab1"
         ...
         xmlns:local="clr-namespace:BindingBetweenFiles"
         mc:Ignorable="d" 
         DataContext="local:MainWindow"
         d:DesignHeight="300" d:DesignWidth="300">
<Grid>
    <Label Content="{Binding DataContext.txtblock1.Text, RelativeSource={
                     RelativeSource AncestorType={x:Type local:MainWindow}}}"/>
</Grid>

I wonder if the declaration of the DataContext is wrong or if the binding is the problem?

I really appreciate any help you can provide.

Answer 1

Assuming all you would want is to be able to bind a string to the Tab1 "text", create a DependencyProperty in the code-behind for the UserControl :

public string TabText
{
    get { return (string)GetValue(TabTextProperty); }
    set { SetValue(TabTextProperty, value); }
}
public static readonly DependencyProperty TabTextProperty = DependencyProperty.Register("TabText", typeof(string), typeof(Tab1), new PropertyMetadata("Default"));

Then in the Tab1 XAML:

<UserControl x:Class="BindingBetweenFiles.Tab1"
     ...
     xmlns:local="clr-namespace:BindingBetweenFiles"
     mc:Ignorable="d" 
     DataContext="local:MainWindow"
     d:DesignHeight="300" d:DesignWidth="300"
     x:Name="tab1Control">
<Grid>
    <Label Content="{Binding ElementName=tab1Control, Path=TabText"/>
</Grid>

Then in your Window XAML:

<local:Tab1 TabText="The text you want to place."/>

Or you can also bind to TabText, eg:

<local:Tab1 TabText="{Binding SomeProperty}"/>