LINQ和对象引用的问题

本文关键字：问题 对象引用 LINQ | 更新日期: 2023-09-27 18:06:38

我一直在尝试让下面几行工作，这里是一个完整的代码示例，可以在Visual Studio中运行，演示了我正在谈论的场景。这里的一切都如预期的那样工作，当我改变玩家的IsReady值时，附加到事件的lambda被触发，if (to)计算结果为true。然而，控制台。WriteLine永远不会被击中，因为在ConcurrentBag中，玩家的IsReady值似乎没有更新。

class Program
{
    public static ConcurrentBag<Player> Players { get; set; }
    static void Main(string[] args)
    {
        Players = new ConcurrentBag<Player>();
        Player player = new Player() { Id = "123" };
        Players.Add(player);
        player.IsReady.ValueChanged += (from, to) =>
        {
            if (to)
            {
                if (Players.All(p => p.IsReady.Value))
                {
                    Console.WriteLine("It worked");
                }
            }
        };
        LookupPlayerById("123").IsReady.Value = true;
    }
    public static Player LookupPlayerById(string clientId)
    {
        var player = Players.FirstOrDefault(x => x.Id == clientId);
        return player;
    }
}
public class Player
{
    public string Id { get; set; }
    public MonitoredValue<bool> IsReady { get; set; }
    public Player()
    {
        IsReady = new MonitoredValue<bool>(false);
    }
}
public class MonitoredValue<T>
{
    public delegate void ValueChangedHandler(T from, T to);
    public event ValueChangedHandler ValueChanged;
    private T m_Value;
    public T Value
    {
        get { return m_Value; }
        set
        {
            if (ValueChanged != null) // if invocation list is not empty, fire the event
            {
                ValueChanged(m_Value, value);
            }
            m_Value = value;
        }
    }
    public MonitoredValue() { }
    public MonitoredValue(T initialValue)
    {
        m_Value = initialValue;
    }
}

LINQ和对象引用的问题

问题是您首先通知侦听器，然后才实际更改值。将属性定义更改为以下代码:

(delegate {}如果默认事件的实现，现在我不需要检查空前每次调用)

public event ValueChangedHandler ValueChanged = delegate {};
public T Value
{
    get { return m_Value; }
    set
    {
        //first change
        m_Value = value;
        //now notify
        ValueChanged(m_Value, value);
    }
}

因为它是一个引用类型，Player将被FirstOrDefault返回的对象引用，除非它是一个Default，这种情况下你没有得到匹配。

示例:

    public static void Main()
    {
        ConcurrentBag<ClassA> test = new ConcurrentBag<ClassA>();
        var hurp = new ClassA();
        hurp.number = 3;
        test.Add(hurp);
        var derp = test.FirstOrDefault();
        derp.number = 4;
        Console.Write(test.FirstOrDefault().number);
        Console.WriteLine(derp.number);
        Console.ReadLine();
    }

打印:44

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