Correct using Cache in ASP.NET

Posted by Dmytro Shteflyuk on under ASP.NET

Often in ASP.NET application we see a code which looks like this one:

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if (Cache["SomeData"] != null)
{
    string name = ((SomeClass) Cache["SomeData"]).Name;
    //.....
}

Experienced developer, even if he is not a paranoiac, will find possible problem immediately — NullReferenceException. That’s because of caching implementation in ASP.NET. In ideal case an object, that has been cached, will stay there up to application restart, but in real world it could be deleted between two calls: by the garbage collector when memory is over (because cache uses weak references WeakReference); by another thread to refresh cached data.

So the code I have mentioned before works in 99% of all cases, but sometimes you will get errors in your log, which can not be reproduced easily. Here is right cache usage approach:

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SomeClass someClass = Cache["SomeData"] as SomeClass;
if (someClass != null)
{
    string name = someClass.Name;
    //.....
}

Do not relax your vigilance, it’s exactly what they are waiting for! (about bugs)

Crazy piece of code: Checking query parameter

Posted by Dmytro Shteflyuk on under ASP.NET

How often you are laughing out loud when looking on the someone’s code? Today I found great code in my current project and I can’t hold posting this to my blog. So,

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if (Request.QueryString.HasKeys())
{
    string[] keys = Request.QueryString.AllKeys;
    foreach (string k in keys)
    {
        if (k == "memberpagemode" && (string)Request.QueryString.GetValues(k).GetValue(0) == "edit")
        {
            pSett.ChangeFormViewMode(FormViewMode.Edit);
        }
    }
}

And how do you search through the hash for a key with specified value?

What the heck? Are Developers of Facebook client libraries for ASP.NET stupid?

Posted by Dmytro Shteflyuk on under ASP.NET

Last week I faced strange bug in Facebook Developer Toolkit. When I tried to call setFBML method (I mentioned it in my previous post) I’ve got an exception about invalid signature. “Haha” I said and downloaded toolkit sources. After some debugging, I’ve found a few lines which just killed me:

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// Compute the MD5 hash of the signature builder
hash = md5.ComputeHash(Encoding.Default.GetBytes(
                           signatureBuilder.ToString().Trim()));

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Generating content for the Facebook’s setFBML method in ASP.NET

Posted by Dmytro Shteflyuk on under ASP.NET

In my current project we decided to build a Facebook application. This is really great platform with many interesting ideas inside, which usually means that you will spend a much time to make your application working as expected. Today I wanna talk about user profiles. Any Facebook application could add some action links, which will be displayed under the user’s picture, and some content for wide or narrow column. Of course, you can use FBML syntax, especially fb:if-... tags set to choose which content to show on specific profiles to concrete users.

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