Question

I have a MyUserControl with the following Xaml:

<TextBox Text="{Binding InputValueProperty}" />

In the MyUserControl.xaml.cs I have:

public string InputValue
{
    get { return (string)GetValue(InputValueProperty); }
    set { SetValue(InputValueProperty, value); }
}
public static readonly DependencyProperty InputValueProperty = 
    DependencyProperty.Register("InputValueProperty", typeof(string), 
    typeof(MyUserControl));

In my MainWindow.xaml I create a user control:

<local:MyUserControl InputValue="My Input" />

Later on in my MainWindow.xaml.cs I am trying to access this string. All instances of MyUserControl are contained in a List and I access them with a foreach.

string temp = userControl.InputValue;

This is always null. In my MainWindow.xaml I can see the “My Input” in the text box of the user control but I can’t ever seem to get it out of there.

Answer 1

You need to implement INotifyPropertyChanged on your class that has the property

    public class YourClassThatHasTheInputValuePropertyInIt: INotifyPropertyChanged
    {
            public event PropertyChangedEventHandler PropertyChanged;
            private void NotifyPropertyChanged(String propertyName)
            {
                if (PropertyChanged != null)
                    PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }

            public string InputValue
            {
                get { return (string)GetValue(InputValueProperty); }
                set { SetValue(InputValueProperty, value);
                      NotifyPropertyChanged("InputValue"); }
     }
    }

This will allow the binding to pick up the property