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MVVM PRISM: Modal Windows by using Interaction Request with Generics

, 19 Sep 2012 CPOL
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How generics can help us in achieving modal windows in WPF PRISM
Animal's Modal View Animal's Modal View


This article pretends to be the continuation of my other article MVVM PRISM: ProgressBar Interaction Request with Asynchronous Command. Here I will try to explain another interesting way to use modal windows in WPF by using PRISM and its way to do interactions. I am not going to enter to explain in detail every functionality of each component because so it is done in the related article above.

I assume you are familiar with WPF, PRISM and MVVM pattern.

How Does PRISM Try to Get Interactions?

If you have read PRISM’s official developer’s guide, you have probably seen the part of the document where it briefly explains the way to achieve modal interaction and you probably have had trouble to understand or get a custom way to extend IInteractionRequest in order to get more than a MessageBox.

Well, let’s focus on the subject. Basically, the main idea is to trigger a TriggerAction<T> on the UI’s thread from the view model by using property binding. Once the trigger has been launched, it will create the UserControl (the modal view) and it will be inserted to the element’s control collection which is holding the TriggerAction<T>.

For that view which the UI’s thread has just created, it will set a callback to a button in order to quit from the modal view and get back to the main view with any result.

Following the Line

The finality of my project is to find a way to show modal views presenting encapsulated data in a class by using the MVVM pattern, and of course trying to do it in the simplest way I can. Then, let’s try generics.

So following the specs, I’m raising the trigger by passing as argument a generic class (GenericInteractionRequestEventArgs<T>) containing a callback and an object with all data to be presented in the modal view. The callback accepts that generic type as parameter.

public class GenericInteractionRequestEventArgs<T> : EventArgs
    public GenericInteractionRequestEventArgs
    (T _entity, Action<T> _callback, Action _cancelCallback) 
        this.CancelCallback = _cancelCallback;
        this.Callback = _callback;
        this.Entity = _entity;

    public Action CancelCallback { get; private set; }
    public Action<T> Callback { get; private set; }
    public T Entity { get; private set; }

public class GenericInteractionAction<T> : TriggerAction<Grid>
    private Dictionary<UIElement, bool> currentState = new Dictionary<UIElement, bool>();

    public static readonly DependencyProperty DialogProperty =
		DependencyProperty.Register("Dialog", typeof(GenericInteractionDialogBase<T>), typeof(GenericInteractionAction<T>), new PropertyMetadata(null));

    public GenericInteractionDialogBase<T> Dialog
	get { return (GenericInteractionDialogBase<T>)GetValue(DialogProperty); }
	set { SetValue(DialogProperty, value); }

    protected override void Invoke(object parameter)
	var args = parameter as GenericInteractionRequestEventArgs<T>;
	this.SetDialog(args.Entity, args.Callback, args.CancelCallback, null);

    private void SetDialog(T entity, Action<T> callback, Action cancelCallback, UIElement element)
	if (this.Dialog is Views.IGenericInteractionView<T>)
		Views.IGenericInteractionView<T> view = this.Dialog as Views.IGenericInteractionView<T>;

		EventHandler handler = null;
		handler = (s, e) =>
			this.Dialog.ConfirmEventHandler -= handler;
			this.Dialog.CancelEventHandler -= handler;

			if (e.ToString() == InteractionType.OK.ToString())

		this.Dialog.ConfirmEventHandler += handler;
		this.Dialog.CancelEventHandler += handler;
		this.Dialog.SetValue(Grid.RowSpanProperty, this.AssociatedObject.RowDefinitions.Count == 0 ? 1 : this.AssociatedObject.RowDefinitions.Count);
		this.Dialog.SetValue(Grid.ColumnSpanProperty, this.AssociatedObject.ColumnDefinitions.Count == 0 ? 1 : this.AssociatedObject.ColumnDefinitions.Count);                

    private void SaveCurrentState()
	IEnumerator en = this.AssociatedObject.Children.GetEnumerator();
	while (en.MoveNext())
		if (en.Current != this.Dialog)
			UIElement element = (UIElement)en.Current;
			this.currentState.Add(element, element.IsEnabled);
			element.IsEnabled = false;

    private void RestorePreviousState()
	foreach (UIElement element in this.currentState.Keys)            
		element.IsEnabled = this.currentState[element];

Once the trigger has been invoked, it creates the modal view and by using its adapter, it sets the generic property of the view model in order to achieve property binding. Then if we modify some data and press on the modal view’s button, it gets back to the main view model by calling the callback and retrieving the object that has been modified. All of this is done thanks to the adapter, which is responsible to interact between the UI’s thread and the view models. In order to achieve all of this, we need to use a generic TriggerAction. That TriggerAction will contain a generic DependencyProperty that it will be the modal view that we want to show. This modal view must be typed like it is defined in the generic TriggerAction.

public interface IGenericAdapter<T>
    IGenericViewModel<T> ViewModel { get; }

public interface IGenericInteractionView<T>
    void SetEntity(T entity);
    T GetEntity();

public interface IGenericViewModel<T> : IGenericInteractionView<T>, INotifyPropertyChanged
    T Entity { get; set; }

On the other hand, we got GenericInteractionDialogBase<T> that extends UserControl, therefore, it is the code behind each modal view. It will be the handler for routing the callbacks to the view model.

public enum InteractionType

public class GenericInteractionDialogBase<T> : UserControl
    class InteractionEventArgs : EventArgs
        internal InteractionType Type { get; private set; }

        internal InteractionEventArgs(InteractionType _type)
            this.Type = _type;

        public override string ToString()
            return this.Type.ToString();

    public GenericInteractionDialogBase() { }

    public event EventHandler ConfirmEventHandler;
    public event EventHandler CancelEventHandler;

    public void Ok()
        this.OnClose(new InteractionEventArgs(InteractionType.OK));

    public void Cancel()
        this.OnClose(new InteractionEventArgs(InteractionType.Cancel));
    private void OnClose(InteractionEventArgs e)
        var handler = (e.Type == InteractionType.OK) ? 
        this.ConfirmEventHandler : this.CancelEventHandler;
        if (handler != null)
            handler(this, e);

Using the Code

From now on, if we want to get a custom modal view, we just need to create three classes.
Taking for example the modal view which presents the Animal class, those classes are...

First of all, we need to create a TriggerAction for Animal implement the generic class. This is necessary in order to be used for raising the trigger from the main view.

public class AnimalInteractionAction : GenericInteractionAction<Animal>


Secondly, we have to create a class for Animal extending GenericInteractionDialogBase. This will be the modal view which once the TriggerAction has been risen, it uses this UserControl as DependencyProperty in the TriggerAction and thanks to that, we are able to retrieve the modal view and set its properties.

public class AnimalInteractionDialog : GenericInteractionDialogBase<animal>


Thirdly, we will create the modal view setting all XAML and implementing methods and properties in its code behind.

public partial class AnimalInteractionDialogView :

AnimalInteractionDialog, IGenericInteractionView<Animal>, IGenericAdapter<Animal>
    private readonly IGenericAdapter<Animal> adapter;

    public AnimalInteractionDialogView()
        this.adapter = new GenericAdapter<Animal>();
        this.DataContext = this.ViewModel;

    public void SetEntity(Animal entity)

    public Animal GetEntity()
        return this.ViewModel.GetEntity();

    public IGenericViewModel<Animal> ViewModel
        get { return this.adapter.ViewModel; }


Lastly, we just need to set the trigger binding in the main view's XAML. It looks like this:

    <Window x:Class="GenericInteractionRequest.MainWindow"
        Title="MainWindow" Height="350" Width="525">

        SourceObject="{Binding NotificationToPerson}">
                            <interactionRequest:PersonInteractionDialogView />

        SourceObject="{Binding NotificationToAnimal}">
                        <interactionRequest:AnimalInteractionDialogView />


        <Button Content="Get People" Height="35" HorizontalAlignment="Left" 
        Margin="12,12,0,0" Name="button1" VerticalAlignment="Top" Width="102" 
        Command="{Binding Path=SetPeopleCommand}"/>
        <Button Content="Get Animal" Height="35" HorizontalAlignment="Left" 
        Margin="120,12,0,0" Name="button2" VerticalAlignment="Top" Width="107" 
        Command="{Binding Path=SetAnimalCommand}"/>
        <TextBlock Height="229" HorizontalAlignment="Left" Margin="12,70,0,0" 
        Name="textBlock1" Text="{Binding Path=Output}" 
        VerticalAlignment="Top" Width="479" />




  • 10/16/2011 - 1st revision 
  • 02/03/2012 - 2st revision (includes cancel callback support)
  • 09/19/2012 - 3rd revision (enable and disable controls behind the modal view)  


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Gerard Castelló Viader
Software Developer
Spain Spain

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Comments and Discussions

GeneralMy vote of 2 Pin
tbayart28-Jul-14 23:34
membertbayart28-Jul-14 23:34 
QuestionIs it possible to move (drag&drop) the dialog? Pin
Member 106200097-Jul-14 3:54
memberMember 106200097-Jul-14 3:54 
GeneralMy Vote of 5 Pin
Dhadhan7-Apr-14 0:59
memberDhadhan7-Apr-14 0:59 
QuestionDoes this work with Silverlight? I believe I only saw WPF mentioned. Pin
Yelnoc48-Oct-13 10:25
memberYelnoc48-Oct-13 10:25 
Questiongran articulo Pin
francesc bernades17-Jan-13 8:07
memberfrancesc bernades17-Jan-13 8:07 
QuestionModal views without callbacks Pin
DaniloCodelines6-Nov-12 1:51
memberDaniloCodelines6-Nov-12 1:51 
AnswerRe: Modal views without callbacks Pin
Gerard Castelló Viader6-Nov-12 5:01
memberGerard Castelló Viader6-Nov-12 5:01 
GeneralRe: Modal views without callbacks Pin
DaniloCodelines6-Nov-12 6:10
memberDaniloCodelines6-Nov-12 6:10 
Thanks, Viader, but only the first modal dialogs I have shown directly as a response to a button click for sake of simplicity in the start of the sample. I have transferred to objects of the TriggerAction type the responsibility to show new modal windows in response to button clicks in modal windows already displayed. The clicks leading to commands in the viewmodels and using these command objects to produce notification events to be handled by InteractionRequestTriguers in the views as you do in your sample. Doing so, I don't mix the action of showing the views with the code in the viewmodels and use the trick in the Invoke method of the TriggerAction objects.

PS.: I forgot to say that, in the example linked above, I used Window objects that have a ShowDialog method and they don't need this trick to be shown as modal dialogs, but in real applications, we often need to show a usercontrol or a control within a panel behaving like a modal window as in this Viader's sample. Sometimes we need to show a window not application modal but modal to only a part of the application window. These are another use cases for this trick.
Questionthis.Raised NULL Pin
jharri2629-Oct-12 10:21
memberjharri2629-Oct-12 10:21 
AnswerRe: this.Raised NULL Pin
Gerard Castelló Viader30-Oct-12 0:34
memberGerard Castelló Viader30-Oct-12 0:34 
GeneralRe: this.Raised NULL Pin
jharri2630-Oct-12 4:09
memberjharri2630-Oct-12 4:09 
GeneralRe: this.Raised NULL Pin
Gerard Castelló Viader30-Oct-12 8:08
memberGerard Castelló Viader30-Oct-12 8:08 
GeneralMy vote of 5 Pin
DaniloCodelines19-Sep-12 6:14
memberDaniloCodelines19-Sep-12 6:14 
GeneralRe: My vote of 5 Pin
Gerard Castelló Viader20-Sep-12 22:52
memberGerard Castelló Viader20-Sep-12 22:52 
GeneralMy vote of 5 Pin
Kanasz Robert19-Sep-12 5:30
mvpKanasz Robert19-Sep-12 5:30 
GeneralRe: My vote of 5 Pin
Gerard Castelló Viader19-Sep-12 5:30
memberGerard Castelló Viader19-Sep-12 5:30 
SuggestionMemory leaks Pin
Member 403158817-Sep-12 16:59
memberMember 403158817-Sep-12 16:59 
GeneralRe: Memory leaks Pin
Gerard Castelló Viader19-Sep-12 4:52
memberGerard Castelló Viader19-Sep-12 4:52 
GeneralRe: Memory leaks Pin
DaniloCodelines19-Sep-12 5:31
memberDaniloCodelines19-Sep-12 5:31 
GeneralRe: Memory leaks Pin
DaniloCodelines19-Sep-12 5:51
memberDaniloCodelines19-Sep-12 5:51 
GeneralRe: Memory leaks Pin
Gerard Castelló Viader21-Sep-12 0:22
memberGerard Castelló Viader21-Sep-12 0:22 
SuggestionRe: Memory leaks Pin
Dhadhan8-Apr-14 2:27
memberDhadhan8-Apr-14 2:27 
QuestionHow about tab Pin
Ole Teilmann Mortensen8-Feb-12 3:33
memberOle Teilmann Mortensen8-Feb-12 3:33 
AnswerRe: How about tab Pin
Gerard Castelló Viader8-Feb-12 7:28
memberGerard Castelló Viader8-Feb-12 7:28 
GeneralRe: How about tab Pin
Jammer15-Mar-12 2:33
memberJammer15-Mar-12 2:33 

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