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Posted 7 Jun 2012

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Get an ApplicationBarIconButton by name (Redux)

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7 Jun 2012CPOL2 min read
How to get an ApplicationBarIconButton by name.

Yesterday, I read a blog post on getting an ApplicationBarIconButton by name. The author made a couple minor errors in the code, which I was going to leave a comment about, except his comment page is broken. So, another excuse to write something for my own blog.

The basics of the article are that in Windows Phone 7 coding, when referencing the ApplicationBar buttons, you never get a direct reference – you have to look the one you want up by name – and the author provided some code:

C#
private ApplicationBarIconButton GetAppBarIconButton(string name)
{
    foreach (var b in ApplicationBar.Buttons)
        if (((ApplicationBarIconButton)b).Text == name)
            return (ApplicationBarIconButton)b;

    return null;
}

That’s rather ugly code for a simple function. What really bothered me was that he didn’t just cast the object – he casted it twice pointlessly.

The author states that this is a bit uglier than you’d expect (and non-LINQ-able) because ApplicationBar.Button returns an IList, and because “the collection of buttons are of type Object, so you need to cast them.” 

Neither of those statements are exactly accurate. The objects in the collection really are of type ApplicationBarIconButton. They just appear to be Object types due to the effect of the IList. Why exactly that property returns an IList instead of the more precise IList<ApplicationBarIconButton> is a mystery known only to the devs at Microsoft.

So, are we stuck with this? No, we can improve that code. “var” is often a very useful keyword, but you must understand what it does. It says “declare this variable of the type of the object presented to initialize it” – which is expressly what we do not want here. The IList is presenting the objects in the Buttons collections as Objects; but we know that they are ApplicationBarIconButtons and we want they treated like that.

C#
private ApplicationBarIconButton GetAppBarIconButton(string name)
{
    foreach (ApplicationBarIconButton b in ApplicationBar.Buttons)
        if (b.Text == name)
            return b;

    return null;
}

Much cleaner, huh? But, let’s return to the author’s original point. He wanted to use LINQ, but was blocked by the IList. However, Microsoft realized that’s often a problem, and wrote a way around it: The Cast<T>() method. It takes a non-generic IList, and a type, and transforms it into an generic IList<T>. With that, the LINQ version is trivial:

C#
private ApplicationBarIconButton GetAppBarIconButton(string name)
{
  return ApplicationBar.Buttons.Cast<ApplicationBarIconButton>().FirstOrDefault(b=>b.Text == name);
}
This article was originally posted at http://feeds.feedburner.com/HonestIllusion

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

James Curran
Software Developer (Senior) NovelTheory LLC
United States United States
20+ years as a developer : Assembly, C, C++ and C# (in that order) with sidelines in ASP/VBScript, ASP.Net, JavaScript, Perl, QuickBasic, VisualBasic, plus a few others which I'm not going to mention because if I did someone might ask me to use them again (shudder)

Microsoft MVP in VC++ (1994-2004)

I also run www.NJTheater.com as a hobby.

Full resume & stuff at NovelTheory.com

Underused blog at HonestIllusion.com

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