Question

我通过了＃34; GetFilesRevisions_Results＆＃34; GetAsync的方法，它将处理它的结果。但我想从＆＃34; GetFilesRevisions_Results＆＃34;返回一个整数。方法。我怎么能做到这一点？提前谢谢！

private int GetVersionNumber(string i_sFileName)
{
    #region Get latest version no.
    int nVerNo = 0;
   // RequestResult result;
    try
    {

    OAuthUtility.GetAsync
       (
       "https://api.dropboxapi.com/1/revisions/auto/",
           new HttpParameterCollection
                        {
                           { "path", i_sFileName },
                           { "access_token", accessToken },
                           { "rev_limit", 1 }
                        },
          callback:  GetFilesRevisions_Results ??? How I can access return variable 
       );
    }
    catch
    { 

    }
    return nVerNo;
    #endregion
}

private int GetFilesRevisions_Results(RequestResult result)
{
    int nVerNo = 0;

    if (result.StatusCode == 200)
    {
        dynamic dynJson = JsonConvert.DeserializeObject(Convert.ToString(result));
        foreach (var item in dynJson)
        {
            nVerNo = Convert.ToInt32(item.rev);
        }

    }
    else
    {
        throw new Exception("Failed to get revisions of files");
    }

    return  nVerNo;
}
#endregion Get version Number

Answer 1

您无法知道何时会调用您的回调，因此返回值不是获取int的正确方法。

您可以使用带有int参数的事件，并在GetFilesRevisions_Results之前的return内调用它。然后，您就可以使用来自任何此事件侦听器的整数值。

Answer 2

您可能想要使用等待句柄：

AutoResetEvent waitHandle = new AutoResetEvent(false);
int nVerNoGlobalTempHolder = 0;

private int GetVersionNumber(string i_sFileName)
{
    #region Get latest version no.
    for (int i = 0; i < 10 && nVerNoGlobalTempHolder != 0; i++)
    {
       //Someone is waiting for this callback already...
       //Do something like:
       Thread.Sleep(500);
    }
    If (nVerNoGlobalTempHolder == 0) throw new Exception("timeout");

   // RequestResult result;
    try
    {

    OAuthUtility.GetAsync
       (
       "https://api.dropboxapi.com/1/revisions/auto/",
           new HttpParameterCollection
                        {
                           { "path", i_sFileName },
                           { "access_token", accessToken },
                           { "rev_limit", 1 }
                        },
          callback:  GetFilesRevisions_Results ??? How I can access return variable 
       );
    }
    catch
    { 

    }
    waitHandle.WaitOne();
    int nVerNo =nVerNoGlobalTempHolder;

    nVerNoGlobalTempHolder = 0;//Reset this in case you have multiple thread calling it
    return nVerNo;    
}


private int GetFilesRevisions_Results(RequestResult result)
{

    if (result.StatusCode == 200)
    {
        dynamic dynJson = JsonConvert.DeserializeObject(Convert.ToString(result));
        foreach (var item in dynJson)
        {
            nVerNoGlobalTempHolder = Convert.ToInt32(item.rev);
        }

    }
    else
    {
        throw new Exception("Failed to get revisions of files");
    }
    WaitHandle.Set();

}

如果有多个线程调用它，它还会实现非常基本的同步。如果您不需要，请在开始时删除for循环

如何从c＃中的回调方法获取返回值

2 个答案: