Question

我需要执行以下操作，但会收到上述错误

class PrioritizedEvent<DelegateType>
{
    private ArrayList delegates;

    public PrioritizedEvent()
    {
        this.delegates = new ArrayList();
    }

    public void AddDelegate(DelegateType d, int priority)
    {
        this.delegates.Add(new PrioritizedDelegate<DelegateType>((Delegate)d,    priority));
        this.delegates.Sort();
    }

    protected class PrioritizedDelegate<DelegateType> : IComparable
    {
        public Delegate d;
        public int priority;

        public PrioritizedDelegate(Delegate d, int priority)
        {
            this.d = d;
            this.priority = priority;
        }
    }
}

我无法将DelegateType D委托给代表

Answer 1

实际上，您无法指定: Delegate约束 - 它根本无法完成（编译器会阻止您）。您可能会发现添加where DelegateType : class非常有用，只是为了停止使用int等，但您无法通过泛型完成此操作。您需要通过object投射：

(Delegate)(object)d

但是，我个人认为你应该存储DelegateType，而不是Delegate，即

protected class PrioritizedDelegate : IComparable
{
    public DelegateType d;
    public int priority;

    public PrioritizedDelegate(DelegateType d, int priority)
    {
        this.d = d;
        this.priority = priority;
    }
}

注意我从上面删除了<DelegateType>：因为它嵌套在泛型类型（PrioritizedEvent<DelegateType>）中，它已经从父类继承了它。

例如：

class PrioritizedEvent<TDelegateType> where TDelegateType : class
{
    private readonly List<PrioritizedDelegate> delegates
        = new List<PrioritizedDelegate>();

    public void AddDelegate(TDelegateType callback, int priority)
    {
        delegates.Add(new PrioritizedDelegate(callback, priority));
        delegates.Sort((x,y) => x.Priority.CompareTo(y.Priority));
    }

    protected class PrioritizedDelegate
    {
        public TDelegateType Callback {get;private set;}
        public int Priority {get;private set;}

        public PrioritizedDelegate(TDelegateType callback, int priority)
        {
            Callback = callback;
            Priority = priority;
        }
    }
}

Answer 2

您的DelegateType完全不受限制。对于所有编译器都知道它可以是int或某个类或委托。

现在通常你可以使用一些约束来限制泛型类型，不幸的是，不允许将它限制为delagate。

Marc Gravell's回答了C# Generics won't allow Delegate Type Constraints为什么会为您提供解决方法的问题。

无法将类型'DelegateType'转换为'System.Delegate'

2 个答案: