fb:editor FBML tag in Facebook applications

Posted by Dmytro Shteflyuk on under ASP.NET

Some time ago I have started posting about Facebook Application Platform (see my posts about setFBML and Facebook libraries for .NET). Today’s topic is fb:editor. As you may see, Facebook has nice look and feel, and all applications usually adapted in some way to its interface. fb:editor FBML tag allows you to create forms which looks just like native ones, but it has great limitation: it generates it’s own form tag, so can’t be used within ASP.NET server form. In this short post I’ll show HTML generated by fb:editor and a way how to use it in your ASP.NET application.

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Coalesce ?? operator in C# 2.0

Posted by Dmytro Shteflyuk on under ASP.NET

Operator ??, that was introduced in the .NET 2.0, takes first place in my top used C# idioms list a long time, but unfortunately it is rarely used in projects I’ve participated. Therefore these snippets could be found in production code very often:

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public string Caption
{
    get { return ViewState["Caption"] != null ? (string) ViewState["Caption"] : ""; }
    set { ViewState["Caption"] = value; }
}

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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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