out形参的一个很好的特性是，即使函数抛出异常，也可以使用它们返回数据。我认为与异步方法最接近的等效方法是使用一个新对象来保存异步方法和调用者都可以引用的数据。另一种方法是在另一个答案中传递一个委托。

请注意，这两种技术都不具有编译器所具有的任何类型的强制。也就是说，编译器不会要求你在共享对象上设置值或调用传入委托。

下面是一个使用共享对象模拟ref和out的示例实现，用于async方法和其他各种ref和out不可用的场景:

class Ref<T>
{
    // Field rather than a property to support passing to functions
    // accepting `ref T` or `out T`.
    public T Value;
}

async Task OperationExampleAsync(Ref<int> successfulLoopsRef)
{
    var things = new[] { 0, 1, 2, };
    var i = 0;
    while (true)
    {
        // Fourth iteration will throw an exception, but we will still have
        // communicated data back to the caller via successfulLoopsRef.
        things[i] += i;
        successfulLoopsRef.Value++;
        i++;
    }
}

async Task UsageExample()
{
    var successCounterRef = new Ref<int>();
    // Note that it does not make sense to access successCounterRef
    // until OperationExampleAsync completes (either fails or succeeds)
    // because there’s no synchronization. Here, I think of passing
    // the variable as “temporarily giving ownership” of the referenced
    // object to OperationExampleAsync. Deciding on conventions is up to
    // you and belongs in documentation ^^.
    try
    {
        await OperationExampleAsync(successCounterRef);
    }
    finally
    {
        Console.WriteLine($"Had {successCounterRef.Value} successful loops.");
    }
}

c# 7+的解决方案是使用隐式元组语法。

    private async Task<(bool IsSuccess, IActionResult Result)> TryLogin(OpenIdConnectRequest request)
    { 
        return (true, BadRequest(new OpenIdErrorResponse
        {
            Error = OpenIdConnectConstants.Errors.AccessDenied,
            ErrorDescription = "Access token provided is not valid."
        }));
    }

返回结果使用方法签名定义的属性名。例句:

var foo = await TryLogin(request);
if (foo.IsSuccess)
     return foo.Result;

out形参的一个很好的特性是，即使函数抛出异常，也可以使用它们返回数据。我认为与异步方法最接近的等效方法是使用一个新对象来保存异步方法和调用者都可以引用的数据。另一种方法是在另一个答案中传递一个委托。

请注意，这两种技术都不具有编译器所具有的任何类型的强制。也就是说，编译器不会要求你在共享对象上设置值或调用传入委托。

下面是一个使用共享对象模拟ref和out的示例实现，用于async方法和其他各种ref和out不可用的场景:

class Ref<T>
{
    // Field rather than a property to support passing to functions
    // accepting `ref T` or `out T`.
    public T Value;
}

async Task OperationExampleAsync(Ref<int> successfulLoopsRef)
{
    var things = new[] { 0, 1, 2, };
    var i = 0;
    while (true)
    {
        // Fourth iteration will throw an exception, but we will still have
        // communicated data back to the caller via successfulLoopsRef.
        things[i] += i;
        successfulLoopsRef.Value++;
        i++;
    }
}

async Task UsageExample()
{
    var successCounterRef = new Ref<int>();
    // Note that it does not make sense to access successCounterRef
    // until OperationExampleAsync completes (either fails or succeeds)
    // because there’s no synchronization. Here, I think of passing
    // the variable as “temporarily giving ownership” of the referenced
    // object to OperationExampleAsync. Deciding on conventions is up to
    // you and belongs in documentation ^^.
    try
    {
        await OperationExampleAsync(successCounterRef);
    }
    finally
    {
        Console.WriteLine($"Had {successCounterRef.Value} successful loops.");
    }
}

您可以通过使用TPL(任务并行库)而不是直接使用await关键字来做到这一点。

private bool CheckInCategory(int? id, out Category category)
    {
        if (id == null || id == 0)
            category = null;
        else
            category = Task.Run(async () => await _context.Categories.FindAsync(id ?? 0)).Result;

        return category != null;
    }

if(!CheckInCategory(int? id, out var category)) return error

对于真正想要保持参数的开发人员，这里可能有另一种解决方法。

将参数更改为数组或List以封装实际值。记得在发送到方法之前初始化列表。返回后，在使用它之前一定要检查值是否存在。小心编码。

下面是@dcastro回答的代码，为c# 7.0修改了命名元组和元组解构，简化了符号:

public async void Method1()
{
    // Version 1, named tuples:
    // just to show how it works
    /*
    var tuple = await GetDataTaskAsync();
    int op = tuple.paramOp;
    int result = tuple.paramResult;
    */

    // Version 2, tuple deconstruction:
    // much shorter, most elegant
    (int op, int result) = await GetDataTaskAsync();
}

public async Task<(int paramOp, int paramResult)> GetDataTaskAsync()
{
    //...
    return (1, 2);
}

有关新的命名元组、元组字面量和元组解构的详细信息，请参见: https://blogs.msdn.microsoft.com/dotnet/2017/03/09/new-features-in-c-7-0/