Question

在this响应中，我提出了以下帮助方法，可以由不同的Task创建者重用，以将事件转换为任务完成源。

// Helper method
static Task<T> TaskFromEventHelper<T>(object target, string eventName, Func<TaskCompletionSource<T>, object> resultSetterFactory) {
    var tcs = new TaskCompletionSource<T>();
    var addMethod = target.GetType().GetEvent(eventName).GetAddMethod();
    var delegateType = addMethod.GetParameters()[0].ParameterType;
    var d = Delegate.CreateDelegate(delegateType, resultSetterFactory(tcs), "Invoke");
    addMethod.Invoke(target, new object[] {d});
    return tcs.Task;
}

// Empty events (Action style)
static Task TaskFromEvent(object target, string eventName) {
    return TaskFromEventHelper(target, eventName, (Func<TaskCompletionSource<object>, object>)(tcs => (Action)(() => tcs.SetResult(null))));
}

// One-value events (Action<T> style)
static Task<T> TaskFromEvent<T>(object target, string eventName) {
    return TaskFromEventHelper(target, eventName, (Func<TaskCompletionSource<T>, object>)(tcs => (Action<T>)(tcs.SetResult)));
}

// Two-value events (Action<T1, T2> or EventHandler style)
static Task<Tuple<T1, T2>> TaskFromEvent<T1, T2>(object target, string eventName) {
    return TaskFromEventHelper(target, eventName, (Func<TaskCompletionSource<Tuple<T1, T2>>, object>)(tcs => (Action<T1, T2>)((t1, t2) => tcs.SetResult(Tuple.Create(t1, t2)))));
}

在我给出的三个例子的每个例子中都使用了helper方法，有一个tcs.SetResult组件，这让我觉得有一种方法可以将它移动到辅助方法，这可能会简化签名，所以也许帮助方法只需要接受Func<?, T>，其中Func将获取event的输出并将其转换为tcs.SetResult所需的任何内容。

即，我认为必须有一种创建助手的方法，所以我可以把它写成

// Empty events (Action style)
static Task TaskFromEvent(object target, string eventName) {
    return TaskFromEventHelper<object>(target, eventName, new Func<object>(() => null));
}

// One-value events (Action<T> style)
static Task<T> TaskFromEvent<T>(object target, string eventName) {
    return TaskFromEventHelper<T>(target, eventName, new Func<T, T>(t => t));
}

// Two-value events (Action<T1, T2> or EventHandler style)
static Task<Tuple<T1, T2>> TaskFromEvent<T1, T2>(object target, string eventName) {
    return TaskFromEventHelper<Tuple<T1, T2>>(target, eventName, new Func<T1, T2, Tuple<T1, T2>>(Tuple.Create));
}

，但这就是为什么我不知道上面?中的Func<?, T>。例如，这个需要?是两个参数。它可以以某种方式传递给object吗？我觉得它有可能，但如果是这样，它需要一些真正的反思魔法。

Answer 1

您可以使用Expression：

static Task<T> TaskFromEventHelper<T>(object target, string eventName, Delegate resultSetter)
{
    var tcs             = new TaskCompletionSource<T>();
    var addMethod       = target.GetType().GetEvent(eventName).GetAddMethod();
    var delegateType    = addMethod.GetParameters()[0].ParameterType;
    var methodInfo      = delegateType.GetMethod("Invoke");
    var parameters      = methodInfo.GetParameters()
                                    .Select(a => Expression.Parameter(a.ParameterType))
                                    .ToArray();

    // building method, which argument count and
    // their types are not known at compile time
    var exp = // (%arguments%) => tcs.SetResult(resultSetter.Invoke(%arguments%))
        Expression.Lambda(
            delegateType,
            Expression.Call(
                Expression.Constant(tcs),
                tcs.GetType().GetMethod("SetResult"),
                Expression.Call(
                    Expression.Constant(resultSetter),
                    resultSetter.GetType().GetMethod("Invoke"),
                    parameters)),
            parameters);

    addMethod.Invoke(target, new object[] { exp.Compile() });
    return tcs.Task;
}

有没有办法在C＃中简化这个反射委托代码？

1 个答案: