Question

这是一个C＃问题，尽管代码是使用Xamarin iOS编写的。我想了解如何将Task方法与异步函数和回调委托相结合。所以在下面的代码示例中，我想调用等待ExecuteGetAsync（）并等待SendAsynchronousRequest（）完成。

private async Task<CustomHttpResponse> ExecuteGetAsync(CustomHttpRequest inRequest)
{
    NSUrlConnection
        .SendAsynchronousRequest(
            (NSUrlRequest)request,
            NSOperationQueue.MainQueue,
            delegate(NSUrlResponse inResponse, NSData inData, NSError inError)
            {
                // Return the response somehow
            });
}

Answer 1

您应该使用TaskCompletionSource类，如下所示：

private Task<CustomHttpResponse> ExecuteGetAsync(CustomHttpRequest inRequest)
{
    var tcs = new TaskCompletionSource<CustomHttpResponse>();

    NSUrlConnection
        .SendAsynchronousRequest(
            (NSUrlRequest)request, //shouldn't this be inRequest?
            NSOperationQueue.MainQueue,
            delegate(NSUrlResponse inResponse, NSData inData, NSError inError)
            {
                bool error = ... //determine if we have an error

                if(error)
                    tcs.SetException(new Exception(".. error message here ..")); //if we have an error, use the SetException method to set the exception for the Task
                else
                {
                    CustomHttpResponse result = ... // if we don't have an error, get result
                    tcs.SetResult(result); //set the result
                }
            });

    return tcs.Task;
}

请注意，该方法不再使用async关键字。

Answer 2

由于您可以访问父作用域，因此可以预先定义结果变量。然后，创建一个等待句柄。当您的代码获得最终响应时，您可以设置结果和句柄，代码会在主范围内返回结果。

private async Task<CustomHttpResponse> ExecuteGetAsync(CustomHttpRequest inRequest)
{
    CustomHttpResponse result = null; // Put initial result here.
    var handle = new AutoResetEvent(false);
    NSUrlConnection
        .SendAsynchronousRequest(
            (NSUrlRequest)request,
            NSOperationQueue.MainQueue,
            delegate(NSUrlResponse inResponse, NSData inData, NSError inError)
            {
                // Return the response somehow
                result = // make your result
                handle.Set();
            });

    handle.WaitOne(10000) // Wait up to 10 seconds for result
    return result;
}

将任务等待与委托相结合

2 个答案: