Binding to custom dependency property - again

Question

The task: implement the simplest Dependency Property ever, which can be used in xaml like that:

<uc:MyUserControl1 MyTextProperty="{Binding Text}"/> 

I think that this answer is quite close. For better readability i copy all my code here (mostly from that answer above).

<UserControl x:Class="Test.UserControls.MyUserControl1"              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"               xmlns:d="http://schemas.microsoft.com/expression/blend/2008"               DataContext="{Binding RelativeSource={RelativeSource Self}}">     <Grid>         <!-- Text is being bound to outward representative property;              Note the DataContext of the UserControl -->         <TextBox Text="{Binding MyTextProperty}"/>     </Grid> </UserControl> 

and

public partial class MyUserControl1 : UserControl {     // The dependency property which will be accessible on the UserControl     public static readonly DependencyProperty MyTextPropertyProperty =         DependencyProperty.Register("MyTextProperty", typeof(string), typeof(MyUserControl1), new UIPropertyMetadata(String.Empty));     public string MyTextProperty     {         get { return (string)GetValue(MyTextPropertyProperty); }         set { SetValue(MyTextPropertyProperty, value); }     }      public MyUserControl1()     {         InitializeComponent();     } } 

And this is my MainWindow.xaml

<Window x:Class="WpfApplication1.MainWindow"         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:uc="clr-namespace:WpfApplication1"         Title="MainWindow" Height="350" Width="525">     <StackPanel Orientation="Vertical">         <uc:MyUserControl1 MyTextProperty="my text goes here"/>         <Button Click="ButtonBase_OnClick" Content="click"/>     </StackPanel> </Window> 

So far, everything works. However, i find this quite not usefull. What i'd need is

<uc:MyUserControl1 MyTextProperty="{Binding Text}"/> 

and being able to change this by setting a DataContext (as you usually do in MVVM)

So i replace the line as above and add my code behind as follows:

public partial class MainWindow : Window, INotifyPropertyChanged {     public MainWindow()     {         InitializeComponent();         Text = "Initial Text";         DataContext = this;     }     private string _Text;     public string Text     {         get { return _Text; }         set         {             if (value != _Text)             {                 _Text = value;                 NotifyPropertyChanged("Text");             }         }     }      private void ButtonBase_OnClick(object sender, RoutedEventArgs e)     {         Text = "clicked";     }      public event PropertyChangedEventHandler PropertyChanged;     private void NotifyPropertyChanged(String info)     {         if (PropertyChanged != null)         {             PropertyChanged(this, new PropertyChangedEventArgs(info));         }     } } 

Neither the "initial Text" nor the "clicked" is displayed... ever. So my question is how to implement a dept. property correctly to be used with

<uc:MyUserControl1 MyTextProperty="{Binding Text}"/> 

Answer 1

The Text property is located on the DataContext of the MainWindow not of the UserControl.

So change this line <uc:MyUserControl1 MyTextProperty="{Binding Text}"/> into this:

<uc:MyUserControl1 MyTextProperty="{Binding Text, ElementName=MyMainWindow}"/> 

Which will tell the Binding that you're talking about the Text element located in you MainWindow. Of course, since in this example I used ElementName, you're going to want to name your window MyMainWindow...

So add this to your MainWindow:

<Window  Name="MyMainWindow" ..... /> 

If you rather not name your window, you can use the RelativeSource FindAncestor binding like this:

<wpfApplication6:MyUserControl1 MyTextProperty="{Binding Text, RelativeSource={RelativeSource FindAncestor, AncestorType=Window}}"/> 

In both ways, you are asking to find the property named 'Text' in the DataContext of the window.