I have a strange problem.
I'm using the MVVM Light framework from GalaSoft and everything so far works fine.
I'm using the messenger system to send messages between ViewModels just fine, until I tried to do the following:
I have a singleton class, GateKeeper, that sends messages.
This class is NOT a ViewModel and thus does not inherit from ViewModelBase.
If it sends a message it is not received anywhere.
I have tried the following:
Letting GateKeeper inherit from ViewModeBase -> No success.
Registering GateKeeper to receive messages, thus seeing if it would catch/receive the message that was actually sent from itself -> No Success.
Changing GateKeeper from Singleton to normal instantiation -> no Success
Creating a MVVM ViewModel that is not connected to a view, and letting it send messages, just like the GateKeeper -> no Success
All my viewModels that are connected to a view can send messages and they will be received.
It almost seems like a viewmodel must be "linked" to a view before the messenger works,but imo. that is a major limitation.
Below is the current, very simplified setup.
Calling ApplicationInitialize on GateKeeper does not trigger a message received on the mainviewmodel nor the GateKeeper class itselves.
I hope that someone has suggestions to this problem.
Thanks..
Example setup:
MainViewModel constructor:
public MainViewModel()
{
Messenger.Default.Register<LoadViewMessage>(this, (message) =>
{
if (message.Sender is GateKeeper) CurrentView = message.View;
else if (message.Sender is LoginViewModel) CurrentView = message.View;
else if (message.Sender is MenuItemBarViewModel) CurrentView = message.View;
});
GateKeeper:
public class GateKeeper : IGateKeeper
{
private readonly IEmployeeService _employeeService;
#region Implementation of IGateKeeper
public void ApplicationInitialize()
{
Messenger.Default.Send<LoadViewMessage>(new LoadViewMessage(ObjectLocator.MainMapView), this);
}
public void LoginSucceeded(Employee employee)
{
//This is where we retrieve the available services for the current employee
//TODO: add methods for retrieving service info from backend
//Send a message that should make the mainview load the map into its currentview property
Messenger.Default.Send(new LoadViewMessage(ObjectLocator.MainMapView), this);
}
#endregion
public GateKeeper(IEmployeeService employeeService)
{
_employeeService = employeeService;
//Test.. Is not triggered
//Just used for debugging, thus nothing happens inhere.
Messenger.Default.Register<LoadViewMessage>(this, (message) =>
{
if (message.Sender is GateKeeper) ;
else if (message.Sender is LoginViewModel) ;
else if (message.Sender is MenuItemBarViewModel);
});
}
Message class: LoadViewMessage
public class LoadViewMessage : MessageBase
{
public UserControl View { get; protected set; }
public LoadViewMessage(UserControl view, object sender): base(sender)
{
View = view;
}
public LoadViewMessage(UserControl view):this(view, null){}
}
PS: ObjectLocator is a NinJect class that handles all instantiation of objects and their lifecycle
#UPDATE
LBugnion (Creator of MVVM Light) pointed out that the problem lied in the send method, where i was actually using a overload of Send that takes a token.
#This will not work in my situation
Messenger.Default.Send(new LoadViewMessage(ObjectLocator.MainMapView), this);
#This WILL work
Messenger.Default.Send(new LoadViewMessage(ObjectLocator.MainMapView, this));
this was supposed to be passed to the loadViewMessage and NOT the Send method as a token
Your problem is on the Send method. You are using the overload of the method that takes a token as second parameter. You are passing "this" as token. It means that you are (probably by mistake) using the sender of the message as token.
If you are sending with a token, you also need to register the receiver with the same token (in that case, the exact same instance than the one used in the Send method). Since you didn't register with a token, the message is never sent by the Messenger, which is an optimization mechanism.
My guess is that you misunderstood the usage of the token in the Send method. Tokens are only here as a way to build a "private messenging network" if you want, where two objects can use the same token to register/send and establish a private communication.
In your case, if you want to send the Sender together with the message, you'll need to save the Sender in the message itself, which is what MessageBase and the derived classes do.
Hope this helps
Laurent
Related
I am writing an application using Prism that contains three modules. First one has a view to configure a "Person", second one is a service that generates that "Person" and third one is the visualization of all people. These three modules communicate with EventAggregator system. But I have problems with the messages on the service one.
In this service module I only have the service implementation and the module definition.
This service is a people manager that receives a message from EventAggregator, creates a "Person" with a task and send a message to the third module with this "Person".
Service:
private List<Person> people = new();
public PeopleControllerService(IEventAggregator eventAggregator, ICommonParametersService commonParameters)
{
this._eventAggregator = eventAggregator;
eventAggregator.GetEvent<GeneratePersonEvent>().Subscribe(GeneratePerson);
this._commonParameters = commonParameters;
}
private void GeneratePerson()
{
Person newPerson = new(this._commonParameters.DefaultPersonTask);
this.People.Add(newPerson);
this._eventAggregator.GetEvent<AssignedPersonEvent>().Publish(newPerson);
}
Module definition:
private PeopleControllerService moduleController;
public void OnInitialized(IContainerProvider containerProvider)
{
IEventAggregator eventAggregator = containerProvider.Resolve<IEventAggregator>();
ICommonParametersService commonParametersService = containerProvider.Resolve<ICommonParametersService>();
this.moduleController = new(eventAggregator, commonParametersService);
}
public void RegisterTypes(IContainerRegistry containerRegistry)
{
}
The problem is that when I send the "GeneratePersonEvent" message it never reaches the PeopleControllerService and the "GeneratePerson" method is never executed.
I've tried using a view and a viewModel, programming the service in the viewModel and assigning the view to a dummy and hidden region in the app and I've verified that it works that way.
Modified module definition:
public void OnInitialized(IContainerProvider containerProvider)
{
IRegionManager regionManager = containerProvider.Resolve<IRegionManager>();
regionManager.RequestNavigate(RegionNames.DummyRegion, "PeopleController");
}
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterForNavigation<PeopleController>();
}
How can I use the EventAggregator without using a dummy view? Do I have to add something in the "RegisterTypes" method? I've tried with:
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.Register<PeopleControllerService>();
}
but it doesn't work either.
I've checked this post: Can I get EventAggregator Subscribe Message without view, viewmodel in prism?, and there it says that it is possible, but doesn't describe how to implement.
Most of the time you want exactly one instance of a service, and you have to tell the container:
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterSingleton<PeopleControllerService>();
}
Also, you want your service to implement an interface so that you can pass different implementations to the consumers of your service, the most obvious case is your tests.
You need to actually create the instance of your service, too. Normally, you inject it into some consumer, but if it's completely decoupled and only talks through the event aggregator, you have to create the instance manually:
// in App.xaml.cs
protected override void OnInitialized()
{
Container.Resolve<PeopleControllerService>();
base.OnInitialized();
}
Hint: if the service implements an interface, the application doesn't need to personally know the controller module.
I'm very newbie in C#\Prism ecosystem.
I want to connect modules via events, but if just send event:
_eventAggregator.GetEvent<LoginSuccessEvent>().Publish(new LoginSuccessEventArgs(user));
then my event handler is not working.
As I understand it happens, because reciever ViewModel is not created (I checked with break point in debugger).
But if I navigate from event sender:
_regionManager.RequestNavigate(RegionNames.RootRegion, "WorksheetListView");
_regionManager.RequestNavigate(RegionNames.WorksheetDetailsRegion, "WorksheetDetailsView");
_eventAggregator.GetEvent<LoginSuccessEvent>().Publish(new LoginSuccessEventArgs(user));
Then before first RequestNavigate command reciever ViewModel constructor is called.
_regionManager = regionManager;
_model = container.Resolve<WorksheetListModel>();
OpenWorksheetCommand = new DelegateCommand(OpenWorksheet);
Worksheets = _model.WorksheetList;
eventAggregator.GetEvent<LoginSuccessEvent>().Subscribe(OnLoginSuccessEvent);
I tried to add ViewModel class registration to reciever module:
_container.RegisterType<WorksheetListViewModel>();
But no luck. I don't want to add this registration to sender, because hard relation is maked.
But I want to have weak relation between modulel and to do navigation from RECIEVER, but not from SENDER. So sender will don't know anything about reciever.
How can I achive this?
Thanks.
It's a bit unclear what you're trying to achieve, but as far as I get it, your problem's that events are there for those instances that are currently alive. It seems you want more of a state, so that view models that are created after the user logged in can check whether a user is logged in and act accordingly.
I suggest you create a service to hold the currently logged in user and keep the event, because they complement each other nicely.
Example:
public interface IUserManager : INotifyPropertyChanged // this is optional if you keep the event
{
// returns null if no user is logged in
string CurrentUserName { get; }
// returns true if user name and password are valid and updates CurrentUserName
bool TryLogin( string userName, string password );
}
Ok. I found a tons of question like ('EventAggregator don't work around modules').
My solution is very easy. I create a instance of my viewmodel, so constructor with event subscribtion is invoked too.
using Microsoft.Practices.Unity;
using Prism.Modularity;
using Prism.Regions;
using Prism.Events;
using Prism.Unity;
using WorksheetListModule.ViewModels;
using WorksheetListModule.Views;
using WorksheetListModule.Models;
namespace WorksheetListModule
{
public class WorksheetListModule : IModule
{
IRegionManager _regionManager;
IUnityContainer _container;
IEventAggregator _eventAggregator;
public WorksheetListModule(RegionManager regionManager, IUnityContainer container, IEventAggregator eventAggregator)
{
_regionManager = regionManager;
_container = container;
_eventAggregator = eventAggregator;
}
public void Initialize()
{
WorksheetListViewModel vm = new WorksheetListViewModel(_regionManager, _container, _eventAggregator);
_container.RegisterInstance<WorksheetListViewModel>(vm);
_container.RegisterType<WorksheetListModel>();
_container.RegisterTypeForNavigation<WorksheetListView>();
_container.RegisterTypeForNavigation<WorksheetDetailsView>();
}
}
}
Key feature here is RegisterInstance function.
So now I can do navigation in event reciever and event sender now don't know any information about reciever internal structure.
I am working on a wpf application using mvvm light toolkit. Whenever something goes outside the business logic we'll prompt the user with the message box and I send the message from view model to view using
Messenger.Default.Send(Token,"Some text message here");
Now I am writing test cases for view models and in some cases, Code Under Test is linked with such message calls. These are exceptions to me but test cases does not treat them exception as long as it is not being called by throw exception("message")
Suggestions.
Assuming you are sending message from VM to View, which handles the actual "showing logic", then just register for the message in your VM tests and verify that it has been sent/received. For example:
[TestMethod]
public void SendSomethingBadHappenedMessageTest()
{
const string expected = "oh noes!";
string actual = null;
// Register for message to ensure message was sent from VM
Messenger.Default.Register<SomethingBadHappenedMessage>(this,
message => actual = message.Message);
// Assuming command triggers Messenger.Send
_viewModel.SomethingBadHappenedCommand.Execute(expected);
Assert.AreEqual(expected, actual);
}
If you test for exceptions, just mark test method with ExpectedException attribute.
I assume you are trying to verify that the business logic detects a problem and the correct message box is being "shown" in your test case. If that's so, here's what I do:
Instead of using messaging, create a UserNotificationService and IUserNotificationService interface. The concrete implementation would be something like:
public class UserNotificationService : IUserNotificationService
{
public void MessageBox(string message)
{
// code to make the message box pop up goes here
}
}
Inject IUserNotificationService in your view model's constructor (you already have SimpleIoC since you are using mvvm-light) and use it to communicate with the user.
When unit testing, either mock the IUserNotificationService or create a new FakeUserNotificationService class that is capable of verifying the correct message/error was sent. Put that in the constructor of the view model being tested.
public class FakeUserNotificationService : IUserNotificationService
{
public void MessageBox(string message)
{
LastMessage = message;
}
public string LastMessage {get; set;}
}
In your test:
var ns = new FakeUserNotificationService();
var viewModel = new MyViewModel(ns);
viewModel.DoSomethingBad();
Assert.AreEqual(ns.LastMessage, "expected error message");
I have a WPF application which calls WCF service methods through a Client which exposes these methods. Is there any way to bind my application to a property of the service, and to get notified when this property changes? I know INotifyPropertyChanged but I have some doubts about its efficiency in this case... Thanks
EDIT : Actually, all I want is my application to be notified of the changes that happen on the server side.
There are a couple of questsions here. You can bind your code to the client end of a WCF service and by using a partial class definition you can add an INotifyPropertyChanged interface to it so that it meets your design. But actually wiring up the mechanism for pushing updates from the server would be much harder.
In fact, Events will work over WCF, and reasonably performant i.e. you won't have the delay associated with polling. However I wouldn't try to squeeze your WCF code into fitting the INotifyPropertyChanged pattern. Instead use a more bespoke interface for the client/server comms and then expose the INotifyPropertyChanged back in the ViewModel.
Just add a delegate to your service, then call the service from your view model or code behind and reflect the changes with your properties that implement the INotifyPropertyChanged interface:
In Service:
public delegate void ServcieUpdate(SomeDataType data);
public ServcieUpdate OnServcieUpdated { get; set; }
When data is updated:
if (OnServcieUpdated != null) OnServcieUpdated(data);
In view model:
private ServiceClient serviceClient = new ServiceClient();
private ObservableCollection<SomeDataType> data = new
ObservableCollection<SomeDataType>();
public YourViewModel()
{
serviceClient.OnServiceUpdated += OnServcieUpdated;
}
public ObservableCollection<SomeDataType> Data
{
get { return data; }
set { data = value; NotifyPropertyChanged("Data");
}
public void OnServcieUpdated(SomeDataType data)
{
Data = data;
}
Please take a look at the Delegates (C# Programming Guide) page on MSDN in you are unfamiliar with using delegate objects.
If I have two windows in an oob application how do I communicate between them?
This is the new feature of silverlight 5 that allows for multiple windows.
They run in a common application. Hence they share the same static data. The scope of communication choices are therefore very large. Here is an example:-
public class MessageEventArgs : EventArgs
{
public MessageEventArgs(object payload)
{
Payload = payload;
}
public object Payload {get; private set; }
}
public class Messenger
{
private static readonly Messenger _current = new Messenger();
public static Messenger Current { get { return _current; } }
public event EventHandler<MessageEventArgs> MessageReceived;
public void Send(object payload)
{
if (MessageReceived != null)
MessageReceived(this, new MessageEventArgs(payload));
}
}
All windows can attach a handler to Messenger.Current.MessageReceived (just be sure to detach when the window closes) and any window can call Messenger.Current.Send.
Ok so you wouldn't actually use this code its a bit rubbish, the point is Windows in SL5 are not isolated. You can create whatever internal application communication mechanism you need.
Option 1: MVVM Pattern
Both windows share a reference to the same view-model. Changes made by one are seen by both.
Option 2: Normal references
Window A can how a refernce to Windows B when it creates it.
Option 3: Message Passing
You can have a global event that you subscribe to in the Load event. (Make sure you unsubscribe in the Unload event or you will leak memory!) Windows can post messages to that event which the other windows listen for.