Question

Say I have XAML like

<TabControl Grid.Row="1" Grid.Column="2" ItemsSource="{Binding Tabs}" IsSynchronizedWithCurrentItem="True">
    <TabControl.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding TabTitle}" />
        </DataTemplate>
    </TabControl.ItemTemplate>
    <TabControl.ContentTemplate>
        <DataTemplate>
            <local:UserControl1 Text="{Binding Text}" />
        </DataTemplate>
    </TabControl.ContentTemplate>
</TabControl>

I want to ask where does the TabTitle and Text properties come from? I think the should come from each item of Tabs right? Say Tabs is a ObservableCollection<TabViewModel> TabTitle & Text should be from TabViewModel properties right. But it seems true to a certain extend. TabTitle is populated correctly while Text is not.

Text is declared as a Dependency Property in UserControl1 as follows

public string Text
{
    get { return (string)GetValue(TextProperty); }
    set { SetValue(TextProperty, value); }
}

public static readonly DependencyProperty TextProperty =
    DependencyProperty.Register("Text", typeof(string), typeof(UserControl1), new UIPropertyMetadata(""));

When I have tabs not bound to a ObservableCollection<TabViewModel> bindings works fine

<TabControl Grid.Row="1" Grid.Column="1">
    <TabItem Header="Tab 1">
        <local:UserControl1 Text="Hello" />
    </TabItem>
    <TabItem Header="Tab 2">
        <local:UserControl1 Text="World" />
    </TabItem>
</TabControl>

Answer 1

If you are binging UserControl to the property from code-behind file, you should use

 {Binding RelativeSource={RelativeSource Mode=Self}, Path=Text}

Direct binding as u have works only for DataContext