一。使用併發的泛型方法

        static async Task<T> DelayResult<T>(T result,TimeSpan delay)
        {
            await Task.Delay(delay);
            return result;
        }

如何呼叫，點選按鈕，更新文字。

        private async void button1_Click(object sender, EventArgs e)
        {
            this.label1.Text = await
 
 DelayResult<string>("OK", TimeSpan.FromSeconds(5));
             

        }

二。指數退避使用HttpClient訪問

        static async Task<string> DownloadStringWithRetries(string uri)
        {
            using (var client =new HttpClient())
            {
                var nextDelay = TimeSpan.FromSeconds(1
 
);
                for(int i=0;i!=3;++i)
                {
                    try
                    {
                        return await client.GetStringAsync(uri);
                    }
                    catch (Exception)
                    {
                       
                    }
                    
 
await Task.Delay(nextDelay);
                    nextDelay = nextDelay +nextDelay;
                }

                return await client.GetStringAsync(uri);
            }
        }

另外一種超時機制使用Task.WhenAny

        private async Task<string> DownloadStringWithTimeout(string uri)
        {
            using(var client=new HttpClient())
            {
                var downloadTask = client.GetStringAsync(uri);
                var timeoutTask = Task.Delay(2000);
                var completedTask = await Task.WhenAny(downloadTask, timeoutTask);
                if (completedTask == timeoutTask)
                    return null;
                return await downloadTask;
            }
        }