c# - 从子视图 mvvm 返回数据

Question

我第一次在 wpf mvvm 工作，我在“现实生活中的问题”中遇到了一些问题

我有一个带有视图的 ViewModel，我必须从那里打开第二个视图（带有它的 ViewModel，它将有一个对象列表），在这里，我必须选择一个对象，将其返回到第一个 ViewModel，我将使用它。

我正在使用一种简单的方法打开第二个窗口，我知道我有点破坏了 mvvm 模式

public object ShowDialog<TView, TViewModel>(TViewModel dataContext) where TView : IWindow, new() where TViewModel : BaseViewModel<TViewModel>
{
    //Instancio la vista.
    TView view = new TView();    
    WindowService wnd = new WindowService(view);    
    dataContext?.SetWindowService(wnd);    
    view.DataContext = dataContext;         
    view.ShowDialog();
    return dataContext;
}

在 ViewModel 中我像这样打开第二页

WindowService.ShowDialog<ChooseOneCat, ChooseOneCatViewModel>(null);

然后在ChooseOneCatViewModel 中，我让用户选择我以后必须返回的类别

这是我的问题，我怎样才能将该对象提供给第一个视图模型？

Pd：我不使用任何额外的框架。

谢谢！

标签： c#wpfmvvm

Answer 1

我设法使用messenger解决了这个问题，特别是我在Dalstroem 响应中找到的一个实现

源代码：

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;

namespace Application.Messaging
{
    public class Messenger
    {
        private static readonly object CreationLock = new object();
        private static readonly ConcurrentDictionary<MessengerKey, object> Dictionary = new ConcurrentDictionary<MessengerKey, object>();

        #region Default property

        private static Messenger _instance;

        /// <summary>
        /// Gets the single instance of the Messenger.
        /// </summary>
        public static Messenger Default
        {
            get
            {
                if (_instance == null)
                {
                    lock (CreationLock)
                    {
                        if (_instance == null)
                        {
                            _instance = new Messenger();
                        }
                    }
                }

                return _instance;
            }
        }

        #endregion

        /// <summary>
        /// Initializes a new instance of the Messenger class.
        /// </summary>
        private Messenger()
        {
        }

        /// <summary>
        /// Registers a recipient for a type of message T. The action parameter will be executed
        /// when a corresponding message is sent.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="recipient"></param>
        /// <param name="action"></param>
        public void Register<T>(object recipient, Action<T> action)
        {
            Register(recipient, action, null);
        }

        /// <summary>
        /// Registers a recipient for a type of message T and a matching context. The action parameter will be executed
        /// when a corresponding message is sent.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="recipient"></param>
        /// <param name="action"></param>
        /// <param name="context"></param>
        public void Register<T>(object recipient, Action<T> action, object context)
        {
            var key = new MessengerKey(recipient, context);
            Dictionary.TryAdd(key, action);
        }

        /// <summary>
        /// Unregisters a messenger recipient completely. After this method is executed, the recipient will
        /// no longer receive any messages.
        /// </summary>
        /// <param name="recipient"></param>
        public void Unregister(object recipient)
        {
            Unregister(recipient, null);
        }

        /// <summary>
        /// Unregisters a messenger recipient with a matching context completely. After this method is executed, the recipient will
        /// no longer receive any messages.
        /// </summary>
        /// <param name="recipient"></param>
        /// <param name="context"></param>
        public void Unregister(object recipient, object context)
        {
            object action;
            var key = new MessengerKey(recipient, context);
            Dictionary.TryRemove(key, out action);
        }

        /// <summary>
        /// Sends a message to registered recipients. The message will reach all recipients that are
        /// registered for this message type.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="message"></param>
        public void Send<T>(T message)
        {
            Send(message, null);
        }

        /// <summary>
        /// Sends a message to registered recipients. The message will reach all recipients that are
        /// registered for this message type and matching context.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="message"></param>
        /// <param name="context"></param>
        public void Send<T>(T message, object context)
        {
            IEnumerable<KeyValuePair<MessengerKey, object>> result;

            if (context == null)
            {
                // Get all recipients where the context is null.
                result = from r in Dictionary where r.Key.Context == null select r;
            }
            else
            {
                // Get all recipients where the context is matching.
                result = from r in Dictionary where r.Key.Context != null && r.Key.Context.Equals(context) select r;
            }

            foreach (var action in result.Select(x => x.Value).OfType<Action<T>>())
            {
                // Send the message to all recipients.
                action(message);
            }
        }

        protected class MessengerKey
        {
            public object Recipient { get; private set; }
            public object Context { get; private set; }

            /// <summary>
            /// Initializes a new instance of the MessengerKey class.
            /// </summary>
            /// <param name="recipient"></param>
            /// <param name="context"></param>
            public MessengerKey(object recipient, object context)
            {
                Recipient = recipient;
                Context = context;
            }

            /// <summary>
            /// Determines whether the specified MessengerKey is equal to the current MessengerKey.
            /// </summary>
            /// <param name="other"></param>
            /// <returns></returns>
            protected bool Equals(MessengerKey other)
            {
                return Equals(Recipient, other.Recipient) && Equals(Context, other.Context);
            }

            /// <summary>
            /// Determines whether the specified MessengerKey is equal to the current MessengerKey.
            /// </summary>
            /// <param name="obj"></param>
            /// <returns></returns>
            public override bool Equals(object obj)
            {
                if (ReferenceEquals(null, obj)) return false;
                if (ReferenceEquals(this, obj)) return true;
                if (obj.GetType() != GetType()) return false;

                return Equals((MessengerKey)obj);
            }

            /// <summary>
            /// Serves as a hash function for a particular type. 
            /// </summary>
            /// <returns></returns>
            public override int GetHashCode()
            {
                unchecked
                {
                    return ((Recipient != null ? Recipient.GetHashCode() : 0) * >397) ^ (Context != null ?
                    Context.GetHashCode() : 0);
                }
            }
        }
    }
}