c# - 任务FromResult与TaskCompletionSource SetResult

与的功能和含义有何区别？

TaskCompletionSource + SetResult 和 Task + FromResult

在SendAsync方法中？

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    if (request.RequestUri.Scheme != Uri.UriSchemeHttps)
    {
        var response = new HttpResponseMessage(HttpStatusCode.Forbidden) {ReasonPhrase = "HTTPS Required"};
        var taskCompletionSource = new TaskCompletionSource<HttpResponseMessage>();
        taskCompletionSource.SetResult(response);
        return taskCompletionSource.Task;
    }
    return base.SendAsync(request, cancellationToken);
}

protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    if (!request.RequestUri.Scheme.Equals(Uri.UriSchemeHttps, StringComparison.OrdinalIgnoreCase))
    {
        HttpResponseMessage reply = request.CreateErrorResponse(HttpStatusCode.BadRequest, "HTTPS is required for security reason.");
        return Task.FromResult(reply);
    }

    return base.SendAsync(request, cancellationToken);
}

最佳答案

Task.FromResult是.NET 4.5中的新增功能。它是一个帮助程序方法，可创建TaskCompletionSource并调用SetResult。如果使用的是.NET 4或更早版本，则必须使用SetResult。