Question

private Func<Order, OrderResult> GetDispatcherForOrder(Order order)
{
    switch (order.Type)
    {
        case "A":
            return dispatcher => DispatchA(order.Id, order.Info, ...);
        case "B":
            return dispatcher => DispatchB(order.Id, order.Info, ...);
        default:
            throw new ArgumentOutOfRangeException("order.Type");
    }
}

DispatchA和DispatchB返回一个OrderResult对象。我这样称呼它

Order x = GetOrder();
OrderResult myResult = GetDispatcherForOrder(x);

我得到了这个错误

Cannot implicitly convert type 'System.Func<Order, OrderResult>' to 'OrderResult'

我如何获得OrderResult？

Answer 1

当你必须有一个代表时（代码中没有任何内容告诉我你这样做）：

private Func<Order, OrderResult> GetDispatcherForOrder(Order order)
{
    switch (order.Type)
    {
        case "A":
            return dispatcher => DispatchA(order.Id, order.Info, ...);
        case "B":
            return dispatcher => DispatchB(order.Id, order.Info, ...);
        default:
            throw new ArgumentOutOfRangeException("order.Type");
    }
}

Order x = GetOrder();
Func<Order, OrderResult> myFunction = GetDispatcherForOrder;
OrderResult myResult = myFunction(x);

当你需要获得OrderResult的时候：

private OrderResult GetDispatcherForOrder(Order order)
{
    switch (order.Type)
    {
        case "A":
            return DispatchA(order.Id, order.Info, ...);
        case "B":
            return DispatchB(order.Id, order.Info, ...);
        default:
            throw new ArgumentOutOfRangeException("order.Type");
    }
}

Order x = GetOrder();
OrderResult myResult = GetDispatcherForOrder(x);

Answer 2

这是因为您尝试将委托分配给OrderResult对象。我想你可能想写：

Func<Order, OrderResult> myResult = GetDispatcherForOrder(x);

Answer 3

private Func<Order, OrderResult> GetDispatcherForOrder(Order order)

是一个返回委托的方法。但根据您的示例用法：

Order x = GetOrder();
OrderResult myResult = GetDispatcherForOrder(x);

你可能想要这样的东西：

private OrderResult GetDispatcherForOrder(Order order)
{
    switch (order.Type)
    {
        case "A":
            return DispatchA(order.Id, order.Info, ...);
        case "B":
            return DispatchB(order.Id, order.Info, ...);
        default:
            throw new ArgumentOutOfRangeException("order.Type");
    }
}

尝试从委托中返回对象时，“无法隐式转换类型”

3 个答案: