Binding [VisualStateManager] view state to a MVVM viewmodel?

by

Actually you can.
The trick is to make an Attached property and add a property changed callback that actually calls GoToState:

public class StateHelper {
    public static readonly DependencyProperty StateProperty = DependencyProperty.RegisterAttached( 
        "State", 
        typeof( String ), 
        typeof( StateHelper ),
        new UIPropertyMetadata( null, StateChanged ) );

      internal static void StateChanged( DependencyObject target, DependencyPropertyChangedEventArgs args ) {
      if( args.NewValue != null )
        VisualStateManager.GoToState( ( FrameworkElement )target, args.NewValue, true );
    }
  }

You can then set this property in you xaml and add a binding to your viewmodel like any other:

<Window .. xmlns:local="clr-namespace:mynamespace" ..>
    <TextBox Text="{Binding Path=Name, Mode=TwoWay}"
             local:StateHelper.State="{Binding Path=State, Mode=TwoWay}" />
</Window>

Name and State are regular properties in the viewmodel. When Name is set in the viewmodel, either by the binding or something else, it can change the State witch will update the visual state. State could also be set by any other factor and still it would update the view state on the textbox.

Since we’re using a normal binding to bind to Status, we can apply converters or anything else that we’d normally be able to do, so the viewmodel doesn’t have to be aware that its actually setting a visual state name, State could be a bool or an enum or whatever.

You can also use this approach using the wpftoolkit on .net 3.5, but you have to cast target to a Control instead of a FrameworkElement.

Another quick note on visual states, make sure you don’t name your visual states so that they conflict with the built in ones unless you know what you’re doing. This is especially true for validation since the validation engine will try and set its states everytime the binding is updated (and at some other times as well). Go here for a reference on visual state names for diffrent controls.

More Related Contents:

  1. Difference between SelectedItem, SelectedValue and SelectedValuePath
  2. This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread [duplicate]
  3. How can I apply a custom sort rule to a WPF DataGrid?
  4. KeyBinding in UserControl doesn’t work when TextBox has the focus
  5. ItemsControl with multiple DataTemplates for a viewmodel
  6. WPF Animation “Cannot freeze this Storyboard timeline tree for use across threads”
  7. How can I sort a ListBox using only XAML and no code-behind?
  8. What is the difference for TargetType=”{x:Type Button}” and TargetType=”Button”?
  9. Adding a Merged Dictionary to a Merged Dictionary
  10. How can I tell my DataTemplate to bind to a property in the PARENT ViewModel?
  11. Select multiple items from a DataGrid in an MVVM WPF project
  12. The name does not exist in the namespace error in XAML
  13. How to get a group of toggle buttons to act like radio buttons in WPF?
  14. How to create custom window chrome in wpf?
  15. ReSharper WPF error: “Cannot resolve symbol “MyVariable” due to unknown DataContext”
  16. WPF CommandParameter is NULL first time CanExecute is called
  17. Calling a parameterized constructor from XAML
  18. Passing parameters between viewmodels
  19. DataTrigger where value is NOT null?
  20. WPF TreeView: How to style selected items with rounded corners like in Explorer
  21. How can I reduce RadioButton binding code?
  22. Cannot find source for binding with reference ‘RelativeSource FindAncestor’ [duplicate]
  23. Handling the window closing event with WPF / MVVM Light Toolkit
  24. WPF OpenFileDialog with the MVVM pattern? [duplicate]
  25. Different views / data template based on member variable
  26. Combine expander and grid (resizable expander)
  27. WPF: Changing Resources (colors) from the App.xaml during runtime
  28. WPF Context menu on left click
  29. WPF ComboBox without drop-down button
  30. WPF MenuItem.Command binding to ElementName results to System.Windows.Data Error: 4 : Cannot find source for binding with reference

Leave a Comment