将自定义类型属性绑定到自定义控件

Question

I am trying to bind to a user control a property of a custom type (in our exemple, let's call it DataContextOne ). This custom type is composed of two strings.

I then have a user control to which I want to bind this custom type.

The weird thing is that if I put in my control 2 string properties and then try to bind each string from my custom type, it worked. But when I create just a DataContextOne property in my Custom Control and try to bind to it, nothing happens (= null in the user control).

Here is my code

DataContextOne

public class DataContextOne : INotifyPropertyChanged
{
    protected virtual void RaisePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));

    }

    public event PropertyChangedEventHandler PropertyChanged;

    private string _title;
    public string Title 
    {
        get { return _title; }
        set
        {
            if (_title != value)
            {
                _title = value;
                TitleModified = _title + " modified";
                RaisePropertyChanged("Title");
            }
        }
    }

    private string _titlemodified;
    public string TitleModified
    {
        get { return _titlemodified; }
        set
        {
            if (_titlemodified != value)
            {
                _titlemodified = value;
                RaisePropertyChanged("TitleModified");
            }
        }

    }
}

Binding that works

UserControl

public partial class MyUserControl : UserControl
{

    public MyUserControl()
    {
        InitializeComponent();
        (Content as FrameworkElement).DataContext = this;
    }

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

    public static readonly DependencyProperty TextProperty = DependencyProperty.Register(
            "Text",
            typeof(string),
            typeof(MyUserControl),
            null);

    public string TextModified
    {
        get { return (string)GetValue(TextModifiedProperty); }
        set { SetValue(TextModifiedProperty, value); }
    }

    public static readonly DependencyProperty TextModifiedProperty = DependencyProperty.Register(
            "TextModified",
            typeof(string),
            typeof(MyUserControl),
            null);
}

Main Window

code behind

public partial class MainWindow : Window
{
    Random Rnd = new Random();
    DataContextOne dtone = new DataContextOne();

    public MainWindow()
    {
        InitializeComponent();
        dtone.Title = Rnd.Next().ToString();
        DataContext = dtone;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        dtone.Title = Rnd.Next().ToString();
    }
}

xaml:

<local:MyUserControl Grid.Row="1" Text="{Binding Title, UpdateSourceTrigger=PropertyChanged}" TextModified="{Binding TitleModified, UpdateSourceTrigger=PropertyChanged}"/>

Binding that doesn't work

User Control

public partial class MyUserControl : UserControl
{

    public MyUserControl()
    {
        InitializeComponent();
        (Content as FrameworkElement).DataContext = this;
    }

    public DataContextOne dtone 
    {
        get { return (DataContextOne)GetValue(dtoneProperty); }
        set { SetValue(dtoneProperty, value); }
    }

    public static readonly DependencyProperty dtoneProperty = DependencyProperty.Register(
            "dtone",
            typeof(DataContextOne),
            typeof(MyUserControl),
            null);

}

Main Window

Code Behind (note that I bind this )

public partial class MainWindow : Window
{
    Random Rnd = new Random();
    DataContextOne dtone = new DataContextOne();

    public MainWindow()
    {
        InitializeComponent();
        dtone.Title = Rnd.Next().ToString();
        DataContext = this;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        dtone.Title = Rnd.Next().ToString();
    }
}

xaml

<local:MyUserControl Grid.Row="1" dtone="{Binding dtone, UpdateSourceTrigger=PropertyChanged}" Margin="0,31,200,169"/>

I don't understand what is missing. For me it is the same thing with just a custom type that encapsulate the strings on the second version, so why it doesn't work?

Answer 1

{Binding dtone} tries to bind to dtone property of DataContext , which is MainWindow . There is no dtone property in MainWindow class, only a private field, and you cannot bind to fields.

Possible solutions:

• make dtone a property
• or change DataContext = this to DataContext = dtone and {Binding dtone} to {Binding}

Update

Probably unrelated, but there seems to be no reason to have a dtone property in MyUserControl . Why not simple

<local:MyUserControl Grid.Row="1" DataContext="{Binding dtone}" />

without trying to set DataContext manually in MyUserControl constructor?