Wpf – TextBox and default Button binding does update too late

bindingmvvmwpf

I've got a simple WPF dialog with these two controls:

<TextBox Text="{Binding MyText}"/>
<Button Command="{Binding MyCommand}" IsDefault="True"/>

Now, when I enter some text in the TextBox and click the button using the mouse, everything works like expected: the TextBox will set MyText and MyCommand is called.

But when I enter some text and hit enter to "click" the default button, it does not work. Since on hitting enter the focus does not leave the TextBox, the binding will not be refresh MyText. So when MyCommand is called (which works), MyText will contain old data.

How do I fix this in MVVM? In classic code-behind I probably just would call "MyButton.Focus()" in the MyCommand handler, but in MVVM the MyCommand handler does know nothing about the button.

So what now`?

Best Answer

Add the UpdateSourceTrigger to your TextBox with the value PropertyChanged. The default behavior of the Textbox is to update the source, when it´s lost focus.

<TextBox Text="{Binding MyText, UpdateSourceTrigger=PropertyChanged}"/>

Related Solutions

.net – How to automatically select all text on focus in WPF TextBox

We have it so the first click selects all, and another click goes to cursor (our application is designed for use on tablets with pens).

You might find it useful.

public class ClickSelectTextBox : TextBox
{
    public ClickSelectTextBox()
    {
        AddHandler(PreviewMouseLeftButtonDownEvent, 
          new MouseButtonEventHandler(SelectivelyIgnoreMouseButton), true);
        AddHandler(GotKeyboardFocusEvent, 
          new RoutedEventHandler(SelectAllText), true);
        AddHandler(MouseDoubleClickEvent, 
          new RoutedEventHandler(SelectAllText), true);
    }

    private static void SelectivelyIgnoreMouseButton(object sender, 
                                                     MouseButtonEventArgs e)
    {
        // Find the TextBox
        DependencyObject parent = e.OriginalSource as UIElement;
        while (parent != null && !(parent is TextBox))
            parent = VisualTreeHelper.GetParent(parent);

        if (parent != null)
        {
            var textBox = (TextBox)parent;
            if (!textBox.IsKeyboardFocusWithin)
            {
                // If the text box is not yet focussed, give it the focus and
                // stop further processing of this click event.
                textBox.Focus();
                e.Handled = true;
            }
        }
    }

    private static void SelectAllText(object sender, RoutedEventArgs e)
    {
        var textBox = e.OriginalSource as TextBox;
        if (textBox != null)
            textBox.SelectAll();
    }
}

Wpf – Are “{Binding Path=.}” and “{Binding}” really equal

The point of the exception presumably is that you cannot two-way bind a binding-source itself, so it tries to prevent you from creating a binding which does not behave the way you would want it to. By using {Binding Path=.} you just trick the error handling.

(Also it's not unheard of that documentation is erroneous or inaccurate, though i do like the MSDN documentation a lot in general as it usually does contain the crucial points one is interested in)

Best Answer

Related Solutions

.net – How to automatically select all text on focus in WPF TextBox

Wpf – Are “{Binding Path=.}” and “{Binding}” really equal

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