如何将用户控件的文本框中的文本绑定到文本块中？

Question

I create a user Control textbox and i want to bind the textblock to what i type in the user control's textbox. I try some code, but it doesn't work. Anyone can teach me? Thanks

My userControl TextBox:

<Grid  Background="Silver" Style="{StaticResource EntryFieldStyle}"  Width="175" Height="25" Margin="0" >          
    <TextBox Name="watermarkTextBox" Background="Green"   />    
</Grid>

My xaml code:

<StackPanel Orientation="Horizontal">
      <UserControls:WatermarkTextBox x:Name="usernameArea"/>
      <TextBlock Text="{Binding ElementName=usernameArea Path=watermarkTextBox.Text}"  FontSize="13" Foreground="White"/> 
</StackPanel>

Answer 1

Edit2 : One way to do this is using a dependency property along with implementing INotifyPropertyChanged.

What'll happen is that we'll fire a PropertyChangedEvent every time the textbox's text is changed. The Window window will subscribe to this event by accessing WatermarkTextBox's WatermarkText dependency property.

Here's how it looks:

---

WatermarkTextbox.xaml:

<TextBox Name="watermarkTextBox" ...
         TextChanged="watermarkTextBox_TextChanged"/>

WatermarkTextbox.xaml.cs:

public partial class WatermarkTextBox : UserControl, INotifyPropertyChanged
{
    ...
    public static readonly DependencyProperty WatermarkTextProperty =
        DependencyProperty.Register("WatermarkTextProperty", typeof(String),
        typeof(WatermarkTextBox), new PropertyMetadata(null));

    public String WatermarkText
    {
        get { return watermarkTextBox.Text; }
        set { OnPropertyChanged("WatermarkText"); }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string name)
    {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(name));
            }
     }
     private void watermarkTextBox_TextChanged(object sender, TextChangedEventArgs e)
     {
           WatermarkText = this.watermarkTextBox.Text;
     }

}

[MainWindow].xaml:

      <TextBlock Text="{Binding ElementName=usernameArea Path=WatermarkText}" .../> 

Adding a dependency property essentially allows you to expose values in your user control for modification in XAML (as well as bindings, in general).

---

You might also want to change the Foreground (text color) property of the TextBlock to something darker than white, because, by default, the Background is white.