问题描述
我是第一次处理异步任务,但我遇到了一个似乎无法解决的问题。
我有一个使用http请求调用API的方法。
internal static async Task<HttpResponse> CallAPI(string objectname, string parameters, HttpMethod method)
{
HttpResponse r = new HttpResponse();
using (r.HttpClient = new HttpClient())
{
r.HttpClient.BaseAddress = new Uri("https://" + Properties.Settings.Default.APIURL + "/");
r.HttpClient.DefaultRequestHeaders.Clear();
r.HttpClient.DefaultRequestHeaders.Add("Accept", "application/vnd+json;version=1");
r.HttpClient.DefaultRequestHeaders.Add("Host", Properties.Settings.Default.APIURL);
r.HttpClient.DefaultRequestHeaders.Add("Expect", "100-continue");
r.HttpClient.DefaultRequestHeaders.Add("Connection", "Close");
switch (method)
{
case HttpMethod.DELETE:
using (r.ResponseMessage = await r.HttpClient.DeleteAsync("api/" + objectname.ToString() + "/" + parameters))
{
var stopwatch = Stopwatch.StartNew();
r.responseTime = Convert.ToInt32(stopwatch.ElapsedMilliseconds);
r.ResponseData = await r.ResponseMessage.Content.ReadAsStringAsync();
return r;
}
case HttpMethod.GET:
using (r.ResponseMessage = await r.HttpClient.GetAsync("api/" + objectname.ToString() + parameters))
{
var stopwatch = Stopwatch.StartNew();
r.responseTime = Convert.ToInt32(stopwatch.ElapsedMilliseconds);
r.ResponseData = await r.ResponseMessage.Content.ReadAsStringAsync();
return r;
}
default: throw new Exception("No HTTP Method Found");
}
}
我从按钮单击事件调用类中的Delete()方法:
protected void btnDelete_Click(object sender, EventArgs e)
{
Activity a = new Activity();
a.Id = Convert.ToInt32(txtObjectId.text);
//a.Delete(); //void method
bool done = a.Delete().Result; //Task<bool> method
}
如果我将Delete()方法设为空,它将正常工作并返回http响应
public async virtual void Delete()
{
HttpResponse r = new HttpResponse();
r = await CallAPI(_Objectname.ToString(), _Id.ToString(), HttpMethod.DELETE);
}
但如果我尝试将Delete()作为任务,
public async virtual Task<bool> Delete()
{
try
{
HttpResponse r = new HttpResponse();
r = await CallAPI(_Objectname.ToString(), _Id.ToString(), HttpMethod.DELETE);
return true;
}
catch
{
return false;
}
}
它试图执行HTTPCLIENT.deleteasync方法,但应用程序什么都不做。我没有得到异常,它不会冻结,只是看起来不再起作用。
我不知道是什么导致了这种行为,但我对异步编程相当陌生,所以我可能正在做一些我不应该做的事情:-)
推荐答案
如果在使用异步/等待的代码上执行.Result
或.Wait()
you will deadlock your program,则必须使事件处理程序async void
,这是唯一允许您使用async void
的地方。
protected async void btnDelete_Click(object sender, EventArgs e)
{
Activity a = new Activity();
a.Id = Convert.ToInt32(txtObjectId.text);
//await a.Delete(); //Task method
bool done = await a.Delete(); //Task<bool> method
}
如果您最终使用的版本不返回Task<bool>
,Delete()
函数将如下所示
public async virtual Task Delete()
{
HttpResponse r = new HttpResponse();
r = await CallAPI(_Objectname.ToString(), _Id.ToString(), HttpMethod.DELETE);
}
您不需要return
语句。
另外,如果您不需要访问UI,请将.ConfigurateAwait(false)
添加到每个等待调用,以使其不会强制UI线程继续。
public async virtual Task Delete()
{
HttpResponse r = new HttpResponse();
r = await CallAPI(_Objectname.ToString(), _Id.ToString(), HttpMethod.DELETE).ConfigureAwait(false);
}
您也可以对CallAPI
执行相同的操作以使其运行得更好。