Working with the WPF VSM in an MVVM friendly manner
Lately I have been working a lot with Silverlight. While working on my first Silverlight project I encountered my first problem… There are no Triggers in SL!!! At first I was frustrated and started hitting my self in the head but hey SL is not that bad… SL has the Visual State Manager aka VSM which is a pretty awesome tool I must say. I still think SL should have Triggers for some tasks such as ControlTemplates and other tasks yet with VSM you can still get some cool stuff done 
What really strikes me with the VSM is the way it is supported in Blend, and YES designers love VSM! With the VSM they can define states in an easy way (and yes these states transition and the designer has full control on the transitions done). They can navigate easily through states in Blend and even see the transitions being done in Blend there and then.
Going back to WPF one thing that is missing in WPF is a way how a designer can define animations that get Triggered when something happens… Or let me re phrase that…. There is no easy way, or better not as easy as the VSM
Triggers in WPF can invoke Storyboards yet still it feels like the WPF animation system does not have a nice way to dispatch animations… Enter the VSM for WPF.
Yes, VSM is available for WPF as well, and yes it is supported in Blend (you just have to do a little trick that you can find over here)
I created a sample project that leverages the VSM for its animations and yes its all MVVM (in the sample app you’ll see that I am also using design time data for blend and I also included a mini MVVM Libarary that I use to develop my everyday WPF projects ).
Let’s Get Started
So let’s start by defining a state in Blend. In order to do so (assuming you followed the instructions to enable the VSM for WPF projects) you need to navigate to the States Tab and create a new state. Once the state is created and selected you’ll see that Blend will go to recording mode (just like it does when you are doing a normal WPF animation). Now you can change any property of any element and the Blend will record that and create the appropriate transitions for it.
Ok, now that we have the states defined in Blend what is next? well we need a way how to invoke these states for starters!
The Blend team were so kind to give us a Behavior called GoToStateAction. This behavior will basically invoke a state when an event is raised, for example if you have a button that should dispatch a new state, you simple find the GoToStateAction form the Asset tab and drag it on the button
Then you can set the properties for this behavior in the properties tab. There you can specify which state to select.
By doing these steps (define a state and use the GoToStateAction to invoke the state) you are already good to go. You can press F5 and you can see that when you click the button you get transitioned from one state to another. (P.S it’s important that you set a default transition time span otherwise you end up with no transition since the default is 0s).
This is all cool but what about MVVM ??
I hear you I hear you…. What if I have a ViewModel which needs to invoke a state change ?? Unfortunately this is not so straight forward… BUT of course there is a solution… I extended the GoToStateAction so that it can be hooked up from a ViewModel. Here is my extended version
1: public class VisualStateManagerInvoker : GoToStateAction
2: {
3: #region CurrentState
4:
5: /// <summary>
6: /// CurrentState Attached Dependency Property
7: /// </summary>
8: public static readonly DependencyProperty CurrentStateProperty =
9: DependencyProperty.RegisterAttached("CurrentState", typeof(string), typeof(VisualStateManagerInvoker),
10: new PropertyMetadata((string)null,
11: new PropertyChangedCallback(OnCurrentStateChanged)));
12:
13: /// <summary>
14: /// Gets the CurrentState property. This dependency property
15: /// indicates ....
16: /// </summary>
17: public static string GetCurrentState(DependencyObject d)
18: {
19: return (string)d.GetValue(CurrentStateProperty);
20: }
21:
22: /// <summary>
23: /// Sets the CurrentState property. This dependency property
24: /// indicates ....
25: /// </summary>
26: public static void SetCurrentState(DependencyObject d, string value)
27: {
28: d.SetValue(CurrentStateProperty, value);
29: }
30:
31: /// <summary>
32: /// Handles changes to the CurrentState property.
33: /// </summary>
34: private static void OnCurrentStateChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
35: {
36: if (GetGoToStateAction(d) == null)
37: {
38: var command = new RelayCommand(x => //where x is the state name passed as parameter
39: {
40: var stateAction = new VisualStateManagerInvoker();
41: stateAction.Attach(d);
42: stateAction.UseTransitions = GetShouldUseTransition(d);
43: stateAction.StateName = (string)x;
44: stateAction.Invoke(null);
45: });
46: SetGoToStateAction(d, command);
47: }
48: }
49:
50: #endregion
51:
52: #region GoToStateAction
53:
54: /// <summary>
55: /// GoToStateAction Attached Dependency Property
56: /// </summary>
57: public static readonly DependencyProperty GoToStateActionProperty =
58: DependencyProperty.RegisterAttached("GoToStateAction", typeof(ICommand), typeof(VisualStateManagerInvoker),
59: new PropertyMetadata((ICommand)null));
60:
61: /// <summary>
62: /// Gets the GoToStateAction property. This dependency property
63: /// indicates ....
64: /// </summary>
65: public static ICommand GetGoToStateAction(DependencyObject d)
66: {
67: return (ICommand)d.GetValue(GoToStateActionProperty);
68: }
69:
70: /// <summary>
71: /// Sets the GoToStateAction property. This dependency property
72: /// indicates ....
73: /// </summary>
74: public static void SetGoToStateAction(DependencyObject d, ICommand value)
75: {
76: d.SetValue(GoToStateActionProperty, value);
77: }
78:
79: #endregion
80:
81: #region ShouldUseTransition
82:
83: /// <summary>
84: /// ShouldUseTransition Attached Dependency Property
85: /// </summary>
86: public static readonly DependencyProperty ShouldUseTransitionProperty =
87: DependencyProperty.RegisterAttached("ShouldUseTransition", typeof(bool), typeof(VisualStateManagerInvoker),
88: new PropertyMetadata((bool)true));
89:
90: /// <summary>
91: /// Gets the ShouldUseTransition property. This dependency property
92: /// indicates ....
93: /// </summary>
94: public static bool GetShouldUseTransition(DependencyObject d)
95: {
96: return (bool)d.GetValue(ShouldUseTransitionProperty);
97: }
98:
99: /// <summary>
100: /// Sets the ShouldUseTransition property. This dependency property
101: /// indicates ....
102: /// </summary>
103: public static void SetShouldUseTransition(DependencyObject d, bool value)
104: {
105: d.SetValue(ShouldUseTransitionProperty, value);
106: }
107:
108: #endregion
109:
110: }
This class contains 2 attached properties CurrentState (which is a string) and a GoToStateAction which is an ICommand (It also has another property ShouldUseTransition which instructs the VSM weather to use transitions or just change the properties for the new state).
The CurrentState property will attach itself to the DepenedencyObject which is being decorated with this property and hook to its VSM (please note that the attach will crawl up the Logical Tree to find the first available VSM). This operation creates an RelayCommand that is set in the GoToStateAction attached property.
Now the interesting part happens. I created a base class for ViewModels that want to invoke states called StateBaseViewModel. Here is the code…
1: /// <summary>
2: /// Base view model that has a property for state changes
3: /// </summary>
4: public class StateBaseViewModel : BaseViewModel
5: {
6: private string currentState;
7:
8: /// <summary>
9: /// Gets or sets the current state of the ViewModel
10: /// </summary>
11: public string CurrentState
12: {
13: get { return currentState; }
14: set
15: {
16: currentState = value;
17: RaisePropertyChanged("CurrentState");
18: }
19: }
20:
21: /// <summary>
22: /// Changes the CurrentState property to the spcified state
23: /// </summary>
24: public ICommand GoToStateCommand { get; protected set; }
25:
26:
27: /// <summary>
28: /// Specify a command to be fired when state changes
29: /// </summary>
30: public ICommand OnGoToState { get; set; }
31:
32:
33: public StateBaseViewModel()
34: {
35: GoToStateCommand = new RelayCommand(
36: x =>
37: {
38: CurrentState = (string)x;
39: if (OnGoToState != null && OnGoToState.CanExecute(CurrentState))
40: OnGoToState.Execute(CurrentState);
41: },
42: x => !String.IsNullOrEmpty((string)x)
43: );
44: }
45: }
This base view model has the same 2 properties of the VisualStateManagerInvoker. We can make these 2 in sync together by using standard TwoWay databinding. By doing so the VisualStateManagerInvoker will feed the View Model with a command that is hooked up to a UI element VSM and when invoked this will ask the VSM for that element to transition to the state passed as parameter.
Here is the binding for this
1: <local:Checkout
2: mvvmStateManagement:VisualStateManagerInvoker.CurrentState="{Binding CurrentState}"
3: mvvmStateManagement:VisualStateManagerInvoker.GoToStateAction="{Binding OnGoToState, Mode=TwoWay}" />
Assuming that the element local:Checkout has a datacontext set to a view model that is inheriting from StateBaseViewModel, you can see how the VisualStateManagerInvoker is feeding this View model a GoToStateAction by simple two way databinding.
Since this command is now ready to be used from our ViewModel we can invoke a state by simple executing the command like so.
1: CancelCommand = new RelayCommand(x =>
2: {
3: GoToStateCommand.Execute("CancelState");
4: });
This is super awesome isn’t it
Another cool thing about this is that you can use this trick so that you can invoke a state from a child to its parent. Lets say that you have a Window that contains a usercontrol (which has a StateBaseViewModel set as its datacontext) and a button. You want the button to show the UserControl. Ok easy Just drag and drop a GoToStateAction behavior and set its state to the state which makes the user control visible. But now lets say you have a button inside the user control and this button needs to invoke a state defined in the Window. The VSM works with namescopes thus you cannot invoke a state that is out of your namescope. BUT with the approach of uses VisualStateManagerInvoker we can do this since we can set the binding in the same XAML line that declares the usercontrol in the Window thus being in the same namescope as the Window We can then make a normal command that executes the GoToStateCommand in out StateBaseViewModel (this example is in the sample application to Cancel the check out of the shopping list and to show the thank you message when someone checks out the shopping cart)
Please note that the same code works for Silverlight.
Conclusion
I think that by using VSM one makes the Developer Designer workflow a happier thing. Designers love VSM and I learnt to love it as well. Now that I can invoke states easily from my ViewModel. Besides that since the implementation gets the VSM instance in an attached behavior and then feeds it to the ViewModel via databinding, the ViewModel never touches the VSM thus unit testing is much easier like this.
I found this way of working with the VSM awesome… OK I still need to make it cooler but as it is right now you can just grab the code and start working without any problems…. hope it helps 
Download sample application (P.S Open this in Blend 3 to get maximum pleasure )
(Sample application contains MVVMHelper a small library I built for MVVM. It contains loads of goodies… have a look and enjoy)
Some Astoria tips I learnt today
First of all let me start by saying that if you are doing Silverlight, you must learn Astoria, or as they call it nowadays, ADO.NET Data Services..
In a matter of minutes you can expose data from a database in a restful service that can be consumed by Silverlight
Now here are some things I learnt today…
The first tip is How can I have the Service on 1 server and the Silverlight app on another without having Cross Domain issues…
The answer to this is this url
Its important that you install the v1.5 CTP2 since by default this is not the version that comes with .NET 3.5 SP1 (Please note you also have to follow the rest of the steps… )
Another useful tip I learnt today is how to Expand a Property of a Property inside an entity (common when you have many to many relations). Example you have a Venue table that is linked to Sports with a table called VenueSportMapping. You can use XPath like syntax to load the property value.
1: var query = from x in context.Venue.Expand("VenueSportMapping/Sport")
2: select x;
Thats all I have for today… hope you find these 2 tips handy
happy coding
WPF Disciples Resources Page updated
Hey all… I just updated the Resources Page for the WPF Disciples blog. There are loads of goodies in one place… Loads of MVVM toolkits… feel free to dig in
http://wpfdisciples.wordpress.com/resources/
MTS Poland Presentation and sample
As promised, here are the slides and samples for my presentation in Poland on MVVM and Friends.
If you need any help or have any questions feel free to send me an email at marlongrech AT gmail DOT Com (please not I wrote the email in such a way for spam readers)
How to set WPF ScrollViewer VerticalOffset and Horizontal offset
Today I needed to bind to the ScrolViewer VerticalOffset and Horizontal offset to do an animation for them. Yet unfortunately you cannot do this. In order to set these properties you need to use the ScrollToVerticalOffset or ScrollToHorizontalOffset methods :S This is not very good because it means you cannot do DataBinding or animate these properties….
Well as usual I resorted to Attached Behaviour. Basically I created 2 attached properties one for HorizontalOffset and one for VerticalOffset. These properties just call the methods ScrollToVerticalOffset or ScrollToHorizontalOffset inside the property changed handlers… yep it’s as simple as that… Here is the attached behaviour class
1: public class ScrollViewerUtilities
2: {
3: #region HorizontalOffset
4:
5: /// <summary>
6: /// HorizontalOffset Attached Dependency Property
7: /// </summary>
8: public static readonly DependencyProperty HorizontalOffsetProperty =
9: DependencyProperty.RegisterAttached("HorizontalOffset", typeof(double), typeof(ScrollViewerUtilities),
10: new FrameworkPropertyMetadata((double)0.0,
11: new PropertyChangedCallback(OnHorizontalOffsetChanged)));
12:
13: /// <summary>
14: /// Gets the HorizontalOffset property. This dependency property
15: /// indicates ....
16: /// </summary>
17: public static double GetHorizontalOffset(DependencyObject d)
18: {
19: return (double)d.GetValue(HorizontalOffsetProperty);
20: }
21:
22: /// <summary>
23: /// Sets the HorizontalOffset property. This dependency property
24: /// indicates ....
25: /// </summary>
26: public static void SetHorizontalOffset(DependencyObject d, double value)
27: {
28: d.SetValue(HorizontalOffsetProperty, value);
29: }
30:
31: /// <summary>
32: /// Handles changes to the HorizontalOffset property.
33: /// </summary>
34: private static void OnHorizontalOffsetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
35: {
36: var viewer = (ScrollViewer)d;
37: viewer.ScrollToHorizontalOffset((double)e.NewValue);
38: }
39:
40: #endregion
41:
42: #region VerticalOffset
43:
44: /// <summary>
45: /// VerticalOffset Attached Dependency Property
46: /// </summary>
47: public static readonly DependencyProperty VerticalOffsetProperty =
48: DependencyProperty.RegisterAttached("VerticalOffset", typeof(double), typeof(ScrollViewerUtilities),
49: new FrameworkPropertyMetadata((double)0.0,
50: new PropertyChangedCallback(OnVerticalOffsetChanged)));
51:
52: /// <summary>
53: /// Gets the VerticalOffset property. This dependency property
54: /// indicates ....
55: /// </summary>
56: public static double GetVerticalOffset(DependencyObject d)
57: {
58: return (double)d.GetValue(VerticalOffsetProperty);
59: }
60:
61: /// <summary>
62: /// Sets the VerticalOffset property. This dependency property
63: /// indicates ....
64: /// </summary>
65: public static void SetVerticalOffset(DependencyObject d, double value)
66: {
67: d.SetValue(VerticalOffsetProperty, value);
68: }
69:
70: /// <summary>
71: /// Handles changes to the VerticalOffset property.
72: /// </summary>
73: private static void OnVerticalOffsetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
74: {
75: var viewer = (ScrollViewer)d;
76: viewer.ScrollToVerticalOffset((double)e.NewValue);
77: }
78:
79: #endregion
80:
81: }
and here is XAMl of how I use this
1: <Grid>
2: <Grid.RowDefinitions>
3: <RowDefinition />
4: <RowDefinition Height="100"/>
5: </Grid.RowDefinitions>
6: <ScrollViewer x:Name="scrollViewer" HorizontalScrollBarVisibility="Visible" VerticalScrollBarVisibility="Visible" >
7: <Border Width="9000" Height="9000"/>
8: </ScrollViewer>
9:
10: <StackPanel Grid.Row="1">
11: <WrapPanel>
12: <TextBlock Text="Slider for horizontal: Value:" Margin="0,0,10,0"/>
13: <TextBlock Text="{Binding ElementName=scrollViewer, Path=HorizontalOffset}"/>
14: </WrapPanel>
15: <Slider Value="{Binding ElementName=scrollViewer, Path=(local:ScrollViewerUtilities.HorizontalOffset)}"
16: Minimum="0" Maximum="9000"/>
17: <WrapPanel>
18: <TextBlock Text="Slider for vertical: Value:" Margin="0,0,10,0"/>
19: <TextBlock Text="{Binding ElementName=scrollViewer, Path=VerticalOffset}"/>
20: </WrapPanel>
21: <Slider Value="{Binding ElementName=scrollViewer, Path=(local:ScrollViewerUtilities.VerticalOffset)}"
22: Minimum="0" Maximum="9000"/>
23:
24: <WrapPanel>
25: <TextBlock Text="Animate scroll" Margin="0,0,10,0"/>
26: <Button Content="Do it">
27: <Button.Triggers>
28: <EventTrigger RoutedEvent="Button.Click">
29: <BeginStoryboard>
30: <Storyboard>
31: <DoubleAnimation Storyboard.TargetName="scrollViewer"
32: Storyboard.TargetProperty="(local:ScrollViewerUtilities.VerticalOffset)"
33: Duration="0:0:1" DecelerationRatio="1.0" To="8000"/>
34: </Storyboard>
35: </BeginStoryboard>
36: </EventTrigger>
37: </Button.Triggers>
38: </Button>
39: </WrapPanel>
40: </StackPanel>
41: </Grid>
Article revisited: MVVM + M (implementing a Fly Weight TreeView)
Ages ago I wrote an article to introduce an idea that I had for the Mediator pattern to work with MVVM (at that time MVVM was still in the being of its age so I didn’t even call it View Model I called it Controller).
Today I was preparing for a Demo that I will be doing in Poland and I thought to revisit this article and refactor it with the new methods that I discovered over the last year.
What’s new in the new and exciting in the new version.
>> Well for starters I am using a new and improved version of the Mediator. The new version of the Mediator API is much more user friendly. It support Generics and it also eliminates the need to have interfaces implemented for you ViewModel. Instead of implementing an interface and have a switch for the message type now you simple register a message to an Action delegate. The Action delegate can be of a generic type so that you don’t even have to cast the argument. You can read more on this over here.
>> This version also uses Service Locator and the concept of ViewModel Loaders that I introduced in this article.
>> It also uses attached behaviours for the TreeView instead of a ViewModel registering to routed events of the treeview through the EventManager. This is much better! Event Manager registration of event inside a ViewModel can be very dangerous and also makes the ViewModel dirty with references to UI elements. Yet at that time it was an approach that I thought was best, as I said those days were just when View Model concept was emerging…
It’s amazing what I have learnt in the last year and how much MVVM evolved!
Animating width and height when they are Double.NaN
A common problem in WPF when doing animation to width and height is that you cannot animate these properties (or any other properties of type double) if they are by default unset.
Here is a snippet that shows the code that would raise this kind of exception
1: <Border Background="Red" HorizontalAlignment="Center" VerticalAlignment="Center">
2: <TextBlock Text="CLICK ME" VerticalAlignment="Center" HorizontalAlignment="Center"/>
3: <Border.Triggers>
4: <EventTrigger RoutedEvent="UIElement.MouseDown">
5: <BeginStoryboard>
6: <Storyboard>
7: <DoubleAnimation Storyboard.TargetProperty="Height" To="300"/>
8: </Storyboard>
9: </BeginStoryboard>
10: </EventTrigger>
11: </Border.Triggers>
12: </Border>
When you try to do this you get an exception like this one
>> Cannot animate the ‘Height’ property on a ‘System.Windows.Controls.Border’ using a ‘System.Windows.Media.Animation.DoubleAnimation’. For details see the inner exception.
and same for Width.
What I do in order to achieve the same behaviour without the need of setting a default width and height is to use a Scale Transform instead. Here is a snippet to get the same behaviour as the XAML above to animate the height
1: <Border Background="Red" HorizontalAlignment="Center" VerticalAlignment="Center">
2: <TextBlock Text="CLICK ME" VerticalAlignment="Center" HorizontalAlignment="Center"/>
3: <Border.RenderTransform>
4: <ScaleTransform ScaleX="1" ScaleY="1" />
5: </Border.RenderTransform>
6: <Border.Triggers>
7: <EventTrigger RoutedEvent="UIElement.MouseDown">
8: <BeginStoryboard>
9: <Storyboard>
10: <DoubleAnimation Storyboard.TargetProperty="(UIElement.RenderTransform).(ScaleTransform.ScaleY)" To="2"/>
11: </Storyboard>
12: </BeginStoryboard>
13: </EventTrigger>
14: </Border.Triggers>
15: </Border>
Please note that there is a catch here. By using scale transform everything inside the actual control will be scaled. So if that is not what you want then you have a problem.
Yet of course there are solutions…. One of the solutions is to have an attached property to set the Height for you when the control is loaded. This can be achieved by setting the Height/Width to the ActualHeight/ActualWidth. Here is an attached property that I use in such cases.
1: #region SetHeightToActual
2:
3: /// <summary>
4: /// SetHeightToActual Attached Dependency Property
5: /// </summary>
6: public static readonly DependencyProperty SetHeightToActualProperty =
7: DependencyProperty.RegisterAttached("SetHeightToActual", typeof(bool), typeof(WidthHeightBehaviour),
8: new FrameworkPropertyMetadata((bool)false,
9: new PropertyChangedCallback(OnSetHeightToActualChanged)));
10:
11: /// <summary>
12: /// Gets the SetHeightToActual property. This dependency property
13: /// indicates ....
14: /// </summary>
15: public static bool GetSetHeightToActual(DependencyObject d)
16: {
17: return (bool)d.GetValue(SetHeightToActualProperty);
18: }
19:
20: /// <summary>
21: /// Sets the SetHeightToActual property. This dependency property
22: /// indicates ....
23: /// </summary>
24: public static void SetSetHeightToActual(DependencyObject d, bool value)
25: {
26: d.SetValue(SetHeightToActualProperty, value);
27: }
28:
29: /// <summary>
30: /// Handles changes to the SetHeightToActual property.
31: /// </summary>
32: private static void OnSetHeightToActualChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
33: {
34: if ((bool)e.NewValue)
35: {
36: var element = (FrameworkElement)d;
37: RoutedEventHandler handler = null;
38: handler = delegate
39: {
40: element.Height = element.ActualHeight;
41: element.Loaded -= handler;
42: };
43: element.Loaded += handler;
44: }
45: }
46:
47: #endregion
And here is the XAML where I am using the attached behaviour. It is nearly seamless
1: <Border Background="Red" HorizontalAlignment="Center" VerticalAlignment="Center" local:WidthHeightBehaviour.SetHeightToActual="True">
2: <TextBlock Text="CLICK ME" VerticalAlignment="Center" HorizontalAlignment="Center"/>
3: <Border.Triggers>
4: <EventTrigger RoutedEvent="UIElement.MouseDown">
5: <BeginStoryboard>
6: <Storyboard>
7: <DoubleAnimation Storyboard.TargetProperty="Height" To="300"/>
8: </Storyboard>
9: </BeginStoryboard>
10: </EventTrigger>
11: </Border.Triggers>
12: </Border>
You can do the same thing for the Width or any other property of this kind (for example I use this technique also for Center property of ScatterViewItems in Surface development).
Hope this tip/trick helps
Happy coding
Service Locator in MVVM
While doing MVVM one of the common problems to solve is to have the ViewModel consume entities that are “replaceable”. Let me give you an example so that you can better understand what I mean by “replaceable“. Let’s say you have a ViewModel that is using a DataAccess entity to get some data from a data store. You want to be able replace the DataAccess entity so that you can mock this entity for unit testing. Besides this you want to also be able to have some sample data while at design time. And not to forget, when at runtime you want the data access to connects to the database or whatever data store you are using.
In order to do solve this problem I use the ServiceLocator pattern. The Service Locator pattern is very simple. You have a RegisterService method where you register the instance of the service you want to provide and a GetService method which you would use to get the service you want.
Here is the signature of both methods
1: public T GetService<T>()
2:
3: public bool RegisterService<T>(T service)
And here is how to use them in code
1: //get the data access service
2: var dataAccess = GetService<IPeopleDataAccess>();
3:
4: //Register the data access service
5: vm.ServiceLocator.RegisterService<IPeopleDataAccess>(new PeopleDataAccess());
So for example to test the the ViewModel I can write a unit test like this
1: MainViewModel viewModel = new MainViewModel();
2: viewModel.ServiceLocator.RegisterService<IPeopleDataAccess>(new PeopleDataAccessMock());
3:
4: Assert.AreEqual(viewModel.People.Count, PeopleDataAccessMock.PeopleCount,
5: "Invalid number of People returned");
6: Assert.AreEqual(viewModel.People[0].Name, PeopleDataAccessMock.FirstPersonName,
7: "Invalid item in people list");
8: Assert.AreEqual(viewModel.People[0].Surname, PeopleDataAccessMock.FirstPersonSurname,
9: "Invalid item in people list");
So basically in this unit test I am just creating a mock object and testing that my ViewModel is exposing the data from the data access (which is mocked so the data returned by this data access is known in the test context)
This is all cool but now how can I use this in WPF and MVVM. So the first question that people ask is how do I create the ViewModel and set it as the DataContext. And also who is responsible of assigning the services that the ViewModel will consume. In order to do this I use AttachedBehaviour and the Factory design pattern.
I created a simple attached property that accepts a type of a Factory that is responsible for creating the ViewModel and register whatever services it needs. The attached property is very simple, here is the code for it
1: public class ViewModelLoader
2: {
3: #region FactoryType
4:
5: /// <summary>
6: /// FactoryType Attached Dependency Property
7: /// </summary>
8: public static readonly DependencyProperty FactoryTypeProperty =
9: DependencyProperty.RegisterAttached("FactoryType", typeof(Type), typeof(ViewModelLoader),
10: new FrameworkPropertyMetadata((Type)null,
11: new PropertyChangedCallback(OnFactoryTypeChanged)));
12:
13: /// <summary>
14: /// Gets the FactoryType property. This dependency property
15: /// indicates ....
16: /// </summary>
17: public static Type GetFactoryType(DependencyObject d)
18: {
19: return (Type)d.GetValue(FactoryTypeProperty);
20: }
21:
22: /// <summary>
23: /// Sets the FactoryType property. This dependency property
24: /// indicates ....
25: /// </summary>
26: public static void SetFactoryType(DependencyObject d, Type value)
27: {
28: d.SetValue(FactoryTypeProperty, value);
29: }
30:
31: /// <summary>
32: /// Handles changes to the FactoryType property.
33: /// </summary>
34: private static void OnFactoryTypeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
35: {
36: FrameworkElement element = (FrameworkElement)d;
37: IFactory factory = Activator.CreateInstance( GetFactoryType(d) ) as IFactory;
38: if (factory == null)
39: throw new InvalidOperationException("You have to specify a type that inherits from IFactory");
40: element.DataContext = factory.CreateViewModel(d);
41: }
42:
43: #endregion
44:
45: }
and you can use this in XAML like so
1: <Window x:Class="ServiceLocatorSample.Main"
2: xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
3: xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
4: xmlns:vm="clr-namespace:MVVMHelper.Factory;assembly=MVVMHelper"
5: xmlns:fac="clr-namespace:ServiceLocatorSample.ViewModels.Factories"
6: Title="Main" Height="300" Width="300" vm:ViewModelLoader.FactoryType="{x:Type fac:MainViewModelFactory}">
Usually in the implementation of the factory I would check if the current state is at design time or runtime and accordingly register different services. Something like this
1: public class MainViewModelFactory : IFactory
2: {
3: public object CreateViewModel(DependencyObject sender)
4: {
5: var vm = new MainViewModel();
6: if (Designer.IsDesignMode)
7: vm.ServiceLocator.RegisterService<IPeopleDataAccess>(new DesignTimeData.DesignTimePeopleDataAccess());
8: else
9: vm.ServiceLocator.RegisterService<IPeopleDataAccess>(new PeopleDataAccess());
10: return vm;
11: }
12: }
So with this factory at design time I would get Design time data showing in my designer but as soon as I run the app the actual data access (the real one that connects to the database) gets injected.
That’s it for today. Download the sample project and you will have a better idea of how all this works. Any questions or comments please let me know, I will be more than happy to answer
P.S In the sample I have the full MVVMHelper assembly that I use in my everyday work with MVVM so you will also have stuff like Mediator and other things that I will be blogging about very soon
Playing with Shaders: Creating a water effect
Lately I’ve been looking at a really cool project on Codeplex for Pixel Shaders. The set of shaders in this library is awsome and really easy to use in you application….
All you need to do to consume any Shader is add a reference to the WPFShaderEffectLibrary class library and you can start using the shaders in XAML.What is really important is that you install the Shaders Build Task before trying to build the shader library (if you just add a reference to the ready build dlls you don’t even need to do this).
So let’s have a look at how we can use shaders to simulate water on screen.
This is very easy all we need is a ripple shader effect. so something like this
1: <Window.Resources>
2:
3: <Storyboard x:Key="waterAnimMain">
4: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Phase" To="0" From="10" Duration="0:0:2.0" FillBehavior="Stop" />
5: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Amplitude" To="0" From="0.6" Duration="0:0:2.0" FillBehavior="HoldEnd" />
6: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Frequency" To="0" From="30" Duration="0:0:2.5" FillBehavior="HoldEnd" />
7: </Storyboard>
8:
9: </Window.Resources>
10: <Grid Background="Transparent" >
11:
12: <Border>
13: <Border.Background>
14: <LinearGradientBrush EndPoint="0.93,0.925" StartPoint="0.094,0.125">
15: <GradientStop Color="#FF272788" Offset="0.112"/>
16: <GradientStop Color="#FF090916" Offset="0.721"/>
17: <GradientStop Color="#FE222267" Offset="0.28"/>
18: <GradientStop Color="#FE131339" Offset="0.453"/>
19: <GradientStop Color="#FF04040A" Offset="0.974"/>
20: </LinearGradientBrush>
21: </Border.Background>
22:
23: </Border>
24:
25: </Grid>
26:
27: <Window.Effect>
28: <shader:RippleEffect Amplitude="0" Frequency="0" Phase="0" x:Name="rippleMain" />
29: </Window.Effect>
This is our Shader
1: <shader:RippleEffect Amplitude="0" Frequency="0" Phase="0" x:Name="rippleMain" />
And we animate this shader like so to make the effect of water
1: <Storyboard x:Key="waterAnimMain">
2: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Phase" To="0" From="10" Duration="0:0:2.0" FillBehavior="Stop" />
3: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Amplitude" To="0" From="0.6" Duration="0:0:2.0" FillBehavior="HoldEnd" />
4: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Frequency" To="0" From="30" Duration="0:0:2.5" FillBehavior="HoldEnd" />
5: </Storyboard>
We invoke this animation by having a DispatcherTimer trigger the animation every now and then and changing the Center property of the Shader to a random point from 0 to 1.
This already gets us very close but it still does not feel like real water. The trick is to animate to ripple effects at the same time. This will make the ripple effects expand together and thus making the control which has the shader applied look like water. Yet the problem is that you can only apply ONE shader per control. BUT you can have another shader on the parent control and that would still apply the shader on all children (I explain this in this article).
1: <Window.Resources>
2:
3: <Storyboard x:Key="waterAnimMain">
4: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Phase" To="0" From="10" Duration="0:0:2.0" FillBehavior="Stop" />
5: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Amplitude" To="0" From="0.6" Duration="0:0:2.0" FillBehavior="HoldEnd" />
6: <DoubleAnimation Storyboard.TargetName="rippleMain" Storyboard.TargetProperty="Frequency" To="0" From="30" Duration="0:0:2.5" FillBehavior="HoldEnd" />
7: </Storyboard>
8:
9: <Storyboard x:Key="waterAnimSub">
10: <DoubleAnimation Storyboard.TargetName="rippleSub" Storyboard.TargetProperty="Phase" To="0" From="10" Duration="0:0:2.0" FillBehavior="Stop" />
11: <DoubleAnimation Storyboard.TargetName="rippleSub" Storyboard.TargetProperty="Amplitude" To="0" From="0.6" Duration="0:0:2.0" FillBehavior="HoldEnd" />
12: <DoubleAnimation Storyboard.TargetName="rippleSub" Storyboard.TargetProperty="Frequency" To="0" From="30" Duration="0:0:2.5" FillBehavior="HoldEnd" />
13: </Storyboard>
14:
15: </Window.Resources>
16: <Grid Background="Transparent" >
17:
18: <Border>
19: <Border.Background>
20: <LinearGradientBrush EndPoint="0.93,0.925" StartPoint="0.094,0.125">
21: <GradientStop Color="#FF272788" Offset="0.112"/>
22: <GradientStop Color="#FF090916" Offset="0.721"/>
23: <GradientStop Color="#FE222267" Offset="0.28"/>
24: <GradientStop Color="#FE131339" Offset="0.453"/>
25: <GradientStop Color="#FF04040A" Offset="0.974"/>
26: </LinearGradientBrush>
27: </Border.Background>
28: <Border.Effect>
29: <shader:RippleEffect Amplitude="0" Frequency="0" Phase="0" x:Name="ripple" Center="{Binding ElementName=main, Path=(local:MouseBehaviour.LastMouseUp)}" />
30: </Border.Effect>
31: </Border>
32:
33: <Grid.Triggers>
34:
35: <EventTrigger RoutedEvent="UIElement.MouseUp">
36: <BeginStoryboard Storyboard="{StaticResource waterAnim}"/>
37: <BeginStoryboard Storyboard="{StaticResource waterAnimMain}"/>
38: </EventTrigger>
39: </Grid.Triggers>
40:
41: <Grid.Effect>
42: <shader:RippleEffect Amplitude="0" Frequency="0" Phase="0" x:Name="rippleSub" />
43: </Grid.Effect>
44:
45: </Grid>
46:
47: <Window.Effect>
48: <shader:RippleEffect Amplitude="0" Frequency="0" Phase="0" x:Name="rippleMain" />
49: </Window.Effect>
And that’s it. Now we have a perfect water look thanks to the Codeplex Pixel Shader library
I created a sample app that shows all this. The app also has another feature so that you can touch the water by using the mouse and the water would ripple from the point you touch (of course this is with Behaviours so that you can even reuse it )
Happy coding
Installing Surface SDK on Win 7 64 bit
If you like me installed Win7 64 bit you’ll find out that there is a problem with the Surface SDK installer. In order to do this you have to change the installer using ORCA so that it does not do the OS Checks. You also have to do some other black magic… Have a look at this here
: About :
Marlon me = new Marlon();
while(me.UseCSharp) me.Happy = true;
I am currently working at Infusion Development as a Sofware Consultant. I love C# and addicted to the WPF technology…. Here in my blog you will find posts mainly on WPF yet sometimes I blog on other .Net stuff…. I also have an OpenSource project AvalonControlsLibrary that I constantly work on….. I am also an MVP for Client App (see my profile here)
I also happen to have the most beautiful daughter, Jasmine; Thanks Jasmine for being in my life, without you my life would be a mess
Besides programming I also like… mmm… what do I like… ooups, I think I need a hobby or something…..
Anyway, I hope you like my blog, feedback is always appreciated……..
Thanks for the support
Marlon
marlongrech AT gmail DOT com
All posting is provided “AS IS” with no warranties, and confers no rights.
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