wpf - wpf的 Prism vs mvvm灯

Question

我们正在使用 MVVM 项目启动 WPF，并且必须决定使用 PRISM 或 MVVM Light(我对这两个框架都是新手)。我已经阅读了一些帖子，但仍有一些问题。有人可以对以下方面进行一些说明吗？两个框架？:

性能:无论出于何种原因，任何一个框架都会比另一个框架表现得更好吗？

应用程序内的通信(viewmodel 到 viewmodel 或模块之间等):我读过 MVVM Light 有消息服务，这似乎也相当容易。但 PRISM 似乎没有任何等价物。真的吗？ PRISM 将如何处理交互？

单元测试:已阅读 PRISM 更好地支持单元测试。我们还能在 MVVM Light 中编写 NUNIT 或 VSTS 测试吗？

Answer 1

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 token 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);
    }
}

Prism 的缺点:

它不是完全开源的项目(官方 Prism 存储库是只读的)

2015-10-30 : 现在完全开源了: https://github.com/PrismLibrary/Prism

它不再积极发展

2015-10-30 : 新版 Prism: https://github.com/PrismLibrary/Prism

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。