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Accessing a value in a static method

Hi,

I have this code:

        public static void DownloadLastPostStringInBackground(string address)
        {
            WebClient client = new WebClient();
            Uri uri = new Uri(address);

            // Specify that the DownloadStringCallback method gets called
            // when the download completes.
            client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(DownloadLastPostStringCallback);
            client.DownloadStringAsync(uri);
        }

        private static void DownloadLastPostStringCallback(Object sender, DownloadStringCompletedEventArgs e)
        {
            // If the request was not canceled and did not throw
            // an exception, display the resource.
            if (!e.Cancelled && e.Error == null)
            {
                string textString = (string)e.Result;

                Check(Convert.ToInt32(textString));
            }
        }

Now Check() method called from DownloadLastPostStringCallback is not a static method (I can't make it static because I'm changing the properties of some control from it) and therefore I'm getting an error message saying:

Error      1      An object reference is required for the nonstatic field, method, or property '....FormStartup.Check(int)'      ...      225      17      ...

Your help would be appreciated.
0
EEssam
Asked:
EEssam
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2 Solutions
 
gregoryyoungCommented:
make them not static ....
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static-voidCommented:
what static means is that it doesnt need anything to be instanstiated before you run the code. Ie it only relies on static members and constants. If you need to use soemthing non static you cant declare the function as static.
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EEssamAuthor Commented:
There should be a solution.
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static-voidCommented:
not a tidy one. You could staticly instanstiate your class somewhere and call the function on the static version of itself but why on earth would you do that?
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gregoryyoungCommented:
Why is it important that these methods are static? there is almost no overhead for making this an instance method unless you have millions of instances
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EEssamAuthor Commented:
Good question. Check here:

http://msdn2.microsoft.com/en-us/library/system.net.downloadstringcompletedeventargs(VS.80).aspx

Thread Safety
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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static-voidCommented:
ummmm thread safety is a completely seperate issue, if your trying to break into a non-thread safe meathod from something you want to be thread safe then your going to have issues. The only thing i can think of for you is to instansiate your class and call tmp.Check(). You cant have a static member access a non static one, it just wont work.
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EEssamAuthor Commented:
I just removed "static" keyword from the two methods and they still work.

What may be the side effect?

I'm not experienced in C# or .NET.

Please advise.
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gregoryyoungCommented:
EEssam you are missing the concept of static methods and thread safety there ...

It is saying that if *IT* has a method that is static you can assume it to be thread-safe but instance methods it defines are to be assumed to be non-thread-safe ...

This is a disclaimer on every page in MSDN ... It does not apply to your code ...

Cheers,

Greg
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gregoryyoungCommented:
both of your methods look fine (they don't access internal state). The one I would have worries about is your Check() method ... Does it change internal state in a non-atomic way (i.e. is it ok to be re-entrant?). You can put up code for it if you like and I can probablytell you but if it calls other methods then I would need to see them too most likely.
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static-voidCommented:
potential issue with thread safety is that you get a concurrent access problem if two things try to change an object at the same time. You need to make sure that your code wont do this.
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