DataTrigger Binding in WPF Style

.net, c#, mvvm, wpf

Solution

could you provide me an example of what you explained?

Sure,

1 - Using Tag

In your `Style` have your `DataTrigger` as:

<DataTrigger Binding="{Binding Path=Tag,
                                RelativeSource={RelativeSource Self}}"
              Value="{x:Static sys:String.Empty}">
  ...
</DataTrigger>

as for usage:

<Button x:Name="btnPosition"
            Grid.Row="0"
            Grid.Column="0"
            HorizontalAlignment="Left"
            VerticalAlignment="Center"
            Command="{Binding PositionFilterCommand}"
            Content="{l:Translate position}"
            Tag="{Binding SelectedPositions}"
            Style="{StaticResource NewButtonStyle}" />

2 - Using Attached Property:

"local:" refers to the xaml namespace alias of your application or if you use different namespaces, the namespace where `MyCustomPropertyCollection` is declared.

code-behind:

public class MyCustomPropertyCollection {
  public static readonly DependencyProperty SomeStringProperty =
    DependencyProperty.RegisterAttached(
      "SomeString",
      typeof(string),
      typeof(MyCustomPropertyCollection),
      new FrameworkPropertyMetadata(string.Empty));

  public static void SetSomeString(UIElement element, string value) {
    element.SetValue(SomeStringProperty, value);
  }

  public static string GetSomeString(UIElement element) {
    return (string)element.GetValue(SomeStringProperty);
  }
}

`Style.DataTrigger`

<DataTrigger Binding="{Binding Path=(local:MyCustomPropertyCollection.SomeString),
                                RelativeSource={RelativeSource Self}}"
              Value="{x:Static sys:String.Empty}">
  ...
</DataTrigger>

usage:

<Button x:Name="btnPosition"
            Grid.Row="0"
            Grid.Column="0"
            HorizontalAlignment="Left"
            VerticalAlignment="Center"
            Command="{Binding PositionFilterCommand}"
            Content="{l:Translate position}"
            local:MyCustomPropertyCollection.SomeString="{Binding SelectedPositions}"
            Style="{StaticResource NewButtonStyle}" />

3 - Normal Dependency Property

custom `Button` class:

public class MyButton : Button {
  public static readonly DependencyProperty SomeStringProperty =
    DependencyProperty.Register(
      "SomeString",
      typeof(string),
      typeof(MyButton),
      new FrameworkPropertyMetadata(string.Empty));

  public string SomeString {
    get {
      return (string)GetValue(SomeStringProperty);
    }
    set {
      SetValue(SomeStringProperty, value);
    }
  }
}

Style in xaml not only needs `DataTrigger` updated but `Style` definition too.

so switch

<Style x:Key="NewButtonStyle" TargetType="{x:Type Button}">

to

<Style x:Key="NewButtonStyle" TargetType="{x:Type local:MyButton}">

`Style.DataTrigger`

<DataTrigger Binding="{Binding Path=SomeString,
                                RelativeSource={RelativeSource Self}}"
              Value="{x:Static sys:String.Empty}">
  ...
</DataTrigger>

usage:

<local:MyButton x:Name="btnPosition"
            Grid.Row="0"
            Grid.Column="0"
            HorizontalAlignment="Left"
            VerticalAlignment="Center"
            Command="{Binding PositionFilterCommand}"
            Content="{l:Translate position}"
            SomeString="{Binding SelectedPositions}"
            Style="{StaticResource NewButtonStyle}" />

`Tag` approach is frowned upon. "Attached Property" is easier to implement but isn't as clear of a indicator of dependencies as a custom class with a normal DP and AP also gets way overused. Take your pick for what you'd prefer.

Problem

Original source