c# - 两个 View 模型之间的通信

Question

我是 MVVM 设计模式的新手，我有这些 View 模型:

ClassAViewModel

public class ClassAViewModel : INotifyPropertyChanged
    {
        private int _nbre = 0;

        public int Nbre
        {
            get
            {
                return _nbre;
            }
            set
            {
                _nbre = value;
                PropertyChanged(this, new PropertyChangedEventArgs("Nbre"));
            }
        }

        #region Events
        public event PropertyChangedEventHandler PropertyChanged;
        #endregion

    }

和ClassBViewModel

 PUBLIC class ClassBViewModel: INotifyPropertyChanged
    {
        private Boolean _IsBiggerthanFive = false;

        public bool IsBiggerthanFive
        {
            get
            {
                return _IsBiggerthanFive;
            }
            set
            {
                _IsBiggerthanFive = value;
                PropertyChanged(this, new PropertyChangedEventArgs("IsBiggerthanFive"));
            }
        }

        #region Events
        public event PropertyChangedEventHandler PropertyChanged;
        #endregion

    }

我需要知道两个 View 模型之间是否存在通知机制，即在我的情况下，如果第一个 View 模型中的 _nbre > 5，第二个 View 模型将被通知并且 的值_IsBiggerthanFive 将被更改。所以:

1. 两个 View 模型如何在不实例化另一个 View 模型的情况下相互通信？
2. 完成这项任务的最佳方法是什么？

Answer 1

我同意其他评论者的观点，即调解器/pub-sub/事件聚合器/messenger 是一个不错的选择。如果您不使用带有内置解决方案的 MVVM 框架，那么我推荐 this simple approach that takes advantage of the Reactive extensions :

public class EventPublisher : IEventPublisher
{
    private readonly ConcurrentDictionary<Type, object> subjects
        = new ConcurrentDictionary<Type, object>();

    public IObservable<TEvent> GetEvent<TEvent>()
    {
        var subject =
            (ISubject<TEvent>) subjects.GetOrAdd(typeof (TEvent),
                        t => new Subject<TEvent>());
        return subject.AsObservable();
    }

    public void Publish<TEvent>(TEvent sampleEvent)
    {
        object subject;
        if (subjects.TryGetValue(typeof(TEvent), out subject))
        {
            ((ISubject<TEvent>)subject)
                .OnNext(sampleEvent);
        }
    }
}

这是您的整个事件聚合器。将它的实例传递到每个 View 模型中，并将其存储为引用。然后创建一个类来存储您的事件详细信息，比方说“ValueChangedEvent”:

public class ValueChangedEvent
{
    public int Value
    {
        get { return _value; }
    }
    private readonly int _value;

    public ValueChangedEvent(int value)
    {
        _value = value;
    }
}

从第一个 View 模型像这样发布:

set
{
    _nbre = value;
    PropertyChanged(this, new PropertyChangedEventArgs("Nbre"));
    _eventPublisher.Publish(new ValueChangedEvent(value));
}

使用GetEvent订阅其他类:

public class ClassBViewModel: INotifyPropertyChanged, IDisposable
{
    private readonly IDisposable _subscriber;

    public ClassBViewModel(IEventPublisher eventPublisher)
    {
        _subscriber = eventPublisher.Subscribe<ValueChangedEvent>(next => 
        {
            IsBiggerthanFive = next.Value > 5;
        });
    }

    public void Dispose()
    {
        _subscriber.Dispose();
    }
}