我刚刚将一个项目从 Prism 转移到 MvvmLight，它似乎工作得更快（非常主观）。
-
Prism 和 MvvmLight 都有 Mediator 实现（Prism 中的 IEventAggregator，MvvmLight 中的 IMessenger）。但与 IEventAggregator 相比，IMessenger 具有更多功能（例如，使用令牌发送消息）并且使用起来更加方便（参见下一项）。
MvvmLight 还有一个更强大的 ViewModelBase 类。
使用 MvvmLight 的应用程序比使用 Prism 的应用程序更容易测试。例如，IMessenger 比 IEventAggregator 更容易模拟。
PrismViewModel.cs
using System;
using Microsoft.Practices.Prism.Events;
using Microsoft.Practices.Prism.ViewModel;
// An ugly empty event class
public class StringEvent : CompositePresentationEvent<string> { }
public sealed class PrismViewModel : NotificationObject
{
private readonly IEventAggregator _eventAggregator;
private string _name;
public PrismViewModel(IEventAggregator eventAggregator)
{
if (eventAggregator == null)
throw new ArgumentNullException("eventAggregator");
_eventAggregator = eventAggregator;
_eventAggregator.GetEvent<StringEvent>().Subscribe(s => Name = s);
}
public string Name
{
get { return _name; }
set
{
// boiler-plate code
if (value == _name)
return;
_name = value;
RaisePropertyChanged(() => Name);
}
}
public void SendMessage(string message)
{
_eventAggregator.GetEvent<StringEvent>().Publish(message);
}
}
PrismViewModelTestCase.cs
using System;
using FluentAssertions;
using Microsoft.Practices.Prism.Events;
using NSubstitute;
using NUnit.Framework;
public class PrismViewModelTestCase
{
private static PrismViewModel CreateViewModel(IEventAggregator eventAggregator = null)
{
// You can't return Substitute.For<IEventAggregator>()
// because it returns null when PrismViewModel's constructor
// invokes GetEvent<StringEvent>() method which leads to NullReferenceException
return new PrismViewModel(eventAggregator ?? CreateEventAggregatorStub());
}
private static IEventAggregator CreateEventAggregatorStub()
{
var eventAggregatorStub = Substitute.For<IEventAggregator>();
eventAggregatorStub.GetEvent<StringEvent>().Returns(Substitute.For<StringEvent>());
return eventAggregatorStub;
}
[Test]
public void Constructor_WithNonNullEventAggregator_ExpectedSubscribesToStringEvent()
{
// Arrange
var stringEventMock = Substitute.For<StringEvent>();
var eventAggregatorStub = Substitute.For<IEventAggregator>();
eventAggregatorStub.GetEvent<StringEvent>().Returns(stringEventMock);
// Act
CreateViewModel(eventAggregatorStub);
// Assert
// With constrained isolation framework you can only mock virtual members
// CompositePresentationEvent<TPayload> has only one virtual Subscribe overload with four parameters
stringEventMock.Received()
.Subscribe(Arg.Any<Action<string>>(), Arg.Any<ThreadOption>(), Arg.Any<bool>(),
Arg.Any<Predicate<string>>());
}
[Test]
public void Name_ExpectedRaisesPropertyChanged()
{
var sut = CreateViewModel();
sut.MonitorEvents();
sut.Name = "any-value";
sut.ShouldRaisePropertyChangeFor(vm => vm.Name);
}
[Test]
public void SendMessage_ExpectedPublishesStringEventThroughEventAggregator()
{
// Arrange
var stringEventMock = Substitute.For<StringEvent>();
var eventAggregatorStub = Substitute.For<IEventAggregator>();
eventAggregatorStub.GetEvent<StringEvent>().Returns(stringEventMock);
var sut = CreateViewModel(eventAggregatorStub);
const string expectedPayload = "any-string-payload";
// Act
sut.SendMessage(expectedPayload);
// Assert
stringEventMock.Received().Publish(expectedPayload);
}
}
MvvmLightViewModel.cs
using System;
using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Messaging;
public sealed class MvvmLightViewModel : ViewModelBase
{
private string _name;
public MvvmLightViewModel(IMessenger messenger)
{
if (messenger == null)
throw new ArgumentNullException("messenger");
// ViewModelBase already have field for IMessenger
MessengerInstance = messenger;
MessengerInstance.Register<string>(this, s => Name = s);
}
public string Name
{
get { return _name; }
set { Set(() => Name, ref _name, value); // Chic! }
}
public void SendMessage(string message)
{
MessengerInstance.Send(message);
}
}
MvvmLightViewModelTestCase.cs
using System;
using FluentAssertions;
using GalaSoft.MvvmLight.Messaging;
using NSubstitute;
using NUnit.Framework;
public class MvvmLightViewModelTestCase
{
private static MvvmLightViewModel CreateViewModel(IMessenger messenger = null)
{
return new MvvmLightViewModel(messenger ?? Substitute.For<IMessenger>());
}
[Test]
public void Constructor_WithNonNullMessenger_ExpectedRegistersToStringMessage()
{
var messengerStub = Substitute.For<IMessenger>();
var sut = CreateViewModel(messengerStub);
messengerStub.Received().Register(sut, Arg.Any<Action<string>>());
}
[Test]
public void Name_ExpectedRaisesPropertyChanged()
{
var sut = CreateViewModel();
sut.MonitorEvents();
sut.Name = "any-value";
sut.ShouldRaisePropertyChangeFor(vm => vm.Name);
}
[Test]
public void SendMessage_ExpectedSendsStringMessageThroughMessenger()
{
var messengerMock = Substitute.For<IMessenger>();
var sut = CreateViewModel(messengerMock);
const string expectedMessage = "message";
sut.SendMessage(expectedMessage);
messengerMock.Received().Send(expectedMessage);
}
}
棱镜的缺点：
-
它不是完全开源的项目（Prism 官方仓库是只读的）
-
它不再积极开发
- 直接使用它的类会导致样板和可读性较差的代码
我认为任何新项目都应该基于现代解决方案和方法。
恕我直言，任何现代 MVVM 框架（如 Catel、Caliburn.Micro、MvvmLight、ReactiveUI）都比 Prism 好得多。