Question

I am trying to implement data binding, and to have TextBox’s text to be update once I click on some button.

XAML:

<TextBox  Text="{Binding Path=Output}" />

Code:

    public MainWindow()
    {
        InitializeComponent();
        DataContext = Search;
        Search.Output = "111";
    }

    public SearchClass Search = new SearchClass();


    private void button1_Click(object sender, RoutedEventArgs e)
    {
        Search.Output = "222";
    }

    public class SearchClass
    {
        string _output;

        public string Output
        {
            get { return _output; }
            set { _output = value; }
        }
    }

When I execute the program, I see “111”, so the binding from MainWindow() works, but if I click a button – the text in the TextBox is not updated (but in the debugger I see that button1_Click is executed and Search.Output is now equal to “222”). What am I doing wrong?

Answer 1

You should implement INotifyPropertyChanged in your SearchClass and then in setter raise the event:

public event PropertyChangedEventHandler PropertyChanged = delegate { };
public string Output
{
    get { return _output; }
    set 
    { 
        _output = value; 
        PropertyChanged(this, new PropertyChangedEventArgs("Output")); 
    }
}

If I understood right, SearchClass is the DataContext for your TextBlock. In this case implementing as above would help.

When WPF see some class as the source of Binding – it tries to cast it to INotifyPropertyChanged and subscribe to PropertyChanged event. And when event is raised – WPF updates the binding associated with sender (first argument of PropertyChanged). It is the main mechanism that makes binding work so smoothly.