如何避免以下重复代码？

Question

I wrote two functions which look similar, how can I optimize them?

Note:

1. AsyncCompletedEventArgs is the base class of DownloadStringCompletedEventArg and UploadStringCompletedEventArgs .

2. Result property is not in the AsyncCompletedEventArgs .

3. DownloadStringCompletedEventArgs has a Error property, if Error is null , then try to access Result property, the exception occurs.

void fun1(DownloadStringCompletedEventArgs e)
{
    try
    {
        string s = e.Result;
    }
    catch (WebException eX)
    {
        HandleWebException();
    }
}

void fun2(UploadStringCompletedEventArgs e)
{
   try
   {
       string s = e.Result;
   }
   catch (WebException eX)
   {
       HandleWebException();
   }
}

Answer 1

You code may be changed to something like below:

    void fun1(DownloadStringCompletedEventArgs e) { Process(e); }

    void fun2(UploadStringCompletedEventArgs e) { Process(e); }

    private void Process(dynamic eventArgs)
    {
        try
        {
            string s = eventArgs.Result;
        }
        catch (WebException e)
        {
            HandleWebException(e);
        }
    }

Answer 2

UploadStringCompletedEventArgs and DownloadCompletedEventArgs both extend AsyncCompletedEventArgs but unfortunately the base class does not define the Result property.

A TryX pattern with a result accessor delegate might be appropriate here:

public bool TryGetResult(Func<string> resultAccessor, out string result)
{
    try
    {
        result = resultAccessor();
        return true;
    }
    catch(WebException)
    {
        HandleWebException();

        result = null;
        return false;
    }
}

void fun1(DownloadStringCompletedEventArgs e)      
{
    string result;
    if (TryGetResult(() => e.Result, out result))
    {
        // Success
    }
}      

void fun2(UploadStringCompletedEventArgs e)      
{      
    string result;
    if (TryGetResult(() => e.Result, out result))
    {
        // Success
    }
}  

I'd recommend trying to work in a check to AsyncCompletedEventArgs.Error , though, as exceptions are quite expensive.

Answer 3

Something like this:

void fun1(DownloadStringCompletedEventArgs e) 
{ 
    var result = Process<string>(e); 
    if (result != null)
    {
        // TODO your logic here
    }
}

void fun2(UploadStringCompletedEventArgs e) 
{
    var result = Process<string>(e); 
    if (result != null)
    {
        // TODO your logic here
    }
}

private T Process<T>(AsyncCompletedEventArgs result)
{
    if (result.Error != null)
        HandleWebException(result.Error);
    else if (!result.Cancelled)
    {
        //var prop = result.GetType().GetProperty("Result");
        //return (T) prop.GetValue(result, null);
        return (T) ((dynamic)result).Result;
    }
    //else // TODO handle cancelled
    return default(T);
}

Answer 4

Maybe you could write a function that takes a parameter of type AsyncCompletedEventArgs (from which both eventArg classes you use inherit) and then attempt to cast it to the correct type in your code. That would allow you to complete both in the same method, but looking at your code it probably wouldn't have much benefit for you. Good luck!