绑定到UserControl的依赖属性

Question

I have a WPF user control that has a DependencyProperty called IsMultiSelect. I want to show hide a Button in the UserControl xaml.

<Button Visibility="{Binding IsMultiSelect, Converter=....}" />

This user control has a ViewModel assigned to the DataContext. The above syntax gives me a binding error due to the property not existing in the view model.

How can I fix this error?

Answer 1

You can target the UserControl in different ways in the binding.

One solution would be to find it by setting a RelativeSource like this:

<Button Visibility="{Binding IsMultiSelect, 
    RelativeSource={RelativeSource AncestorType={x:Type UserControl}},
    Converter=....}" />

Answer 2

Instead of binding to the property from xaml, the property changed handler for the dependency property should change the button's visibility.

public static readonly DependencyProperty IsMultiSelectProperty = DependencyProperty.Register("IsMultiSelect", typeof(bool), typeof(MyUserControl), new PropertyMetadata(false, OnIsMultiSelectPropertyChanged));

private static void OnIsMultiSelectPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
    (sender as MyUserControl).OnIsMultiSelectPropertyChanged(e);
}

private void OnIsMultiSelectPropertyChanged(DependencyPropertyChangedEventArgs e)
{
    MyButton.Visibility = (bool)e.NewValue ? Visibility.Visible : Visibility.Collapsed;
}

public bool IsMultiSelect
{
    get { return (bool)GetValue(IsMultiSelectProperty); }
    set { SetValue(IsMultiSelectProperty, value); }
}

And you can put the converter logic inside OnIsMultiSelectPropertyChanged as well.