异步任务

   createtask();

   async private void createtask()
        {
            try
            {
                await TaskWithoutReturn().ConfigureAwait(false);
            }
            catch (HttpRequestException ex)
            {

            }
            catch (Exception e)
            {
                throw e;
            }

        }

   private async Task TaskWithoutReturn()
        {
            await Task.Delay(0);
            //逻辑处理

        }