Wpf binding problem

Question

I have in my window a rectangle with a tooltip, Clicking the button suppose to change the tooltip text but it doesn't.

XAML:

 <Grid>
    <Grid.RowDefinitions>
        <RowDefinition />
        <RowDefinition />
    </Grid.RowDefinitions>

    <Grid.Resources>
        <ToolTip x:Key="@tooltip">
            <TextBlock Text="{Binding Name}" />
        </ToolTip>
    </Grid.Resources>

    <Rectangle Width="200" Height="200" Fill="LightBlue" VerticalAlignment="Center" HorizontalAlignment="Center"
            ToolTip="{DynamicResource @tooltip}" />
    <Button Click="Button_Click" Grid.Row="1" Margin="20">Click Me</Button>
</Grid>

code behind:

public partial class Window1 : Window
{

    public Window1()
    {
        DataContext = new Person { Name = "A" };
        InitializeComponent();
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        DataContext = new Person { Name = "B" };
    }
}

Answer 1

Change binding to:

Example:

<ToolTip x:Key="@tooltip">
    <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=Self}, Path=Parent.PlacementTarget.DataContext.Name}" />
</ToolTip>

Reason:

The reason this works and yours doesn't is because the TextBlock element never gets notified of a change in a property named Name that you bind to in your code.

To fix that, in this example, TextBlock is bound to Parent (ToolTip) > PlacementTarget (Button) > DataContext (Person) > Name property. Here TextBlock has reference to PlacementTarget which in your case is a Button. Button notifies TextBlock of a change in it's DataContext property value on which notification, TextBlock updates itself.