Question about FindName RSS

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  johnnystock

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  Question about FindName

  Mar 14, 2008 12:08 PM | LINK

  I have a scenario where an event on a user control that is several layers deep in the control heirarchy needs to change the visibility of another usercontrol. The second control does not have the same direct parent or at the same level but is a child of the top level "Page.xaml".

  Currently I'm just getting a null reference when attempting FindName from teh first User Control indicating that it is not finding the second control.  Is there a specific element I need to call FindName on or something else I need to do in order to allow this interaction to take place?

  Thanks in advance for any help.

  John Stockton
  Microsoft Silverlight MVP and RIA Developer at Ascentium
  Co-Author of Silverlight 2 in Action
  
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  RegularKid

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  Re: Question about FindName

  Mar 14, 2008 03:27 PM | LINK

  Someone correct me if I'm wrong, but I'm pretty sure you'll have to use a parent of the second control in order to find it ( in this case use the root element from your Page.xaml ). I believe FindName will only find controls within it's own hierarchy, rather than on a global scope.

  - Bryan

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  johnnystock

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  Re: Question about FindName

  Mar 14, 2008 04:01 PM | LINK

  That's what I was thinking was happening.  Any idea how I can get a reference to the root element from an unknown level of layers deep in the tree?

  John Stockton
  Microsoft Silverlight MVP and RIA Developer at Ascentium
  Co-Author of Silverlight 2 in Action
  
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  RegularKid

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  Re: Question about FindName

  Mar 14, 2008 04:44 PM | LINK

  I would just keep a reference to it in a class somewhere ( I have a singleton "GameInfo" class I use to keep track of things that most other classes will probably need to use like the root canvas, etc. ). So in the Page_Loaded event for the main canvas I setup the GameInfo class with the necessary values so everything else can reference them later in code.
  
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  johnnystock

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  Re: Question about FindName

  Mar 14, 2008 04:54 PM | LINK

  That sounds like it would work perfectly for me, thanks a ton.  Here's a (potentially stupid) follow-up question, how do I scope the object so that it is available to all other classes, like your "GameInfo" class?

  John Stockton
  Microsoft Silverlight MVP and RIA Developer at Ascentium
  Co-Author of Silverlight 2 in Action
  
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  RegularKid

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  Re: Question about FindName

  Mar 14, 2008 05:10 PM | LINK

  The way I did it was making the class a singleton. Here's the entire class ( hopefully the forum doesn't butcher the formatting too much :) :

  using System;
  using System.Windows;
  using System.Windows.Controls;
  using System.Windows.Documents;
  using System.Windows.Ink;
  using System.Windows.Input;
  using System.Windows.Media;
  using System.Windows.Media.Animation;
  using System.Windows.Shapes;
  
  namespace Game
  {
      public class GameInfo
      {
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          // SINGLETON!
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          private static GameInfo gameInfoInstance = new GameInfo();
          public static GameInfo Get()
          {
              return gameInfoInstance;
          }
  
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          // MEMBER VARIABLS
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
  
          // Screen size
          static public double SCREEN_WIDTH = 800.0;
          static public double SCREEN_HEIGHT = 600.0;
  
          // Main canvas object
          public Canvas HostCanvas;
  
          // State manager
          public StateManager stateManager;
      }
  }
  

  Then in my main Page.xaml.cs class I have:

          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          // Page_Loaded()
          //
          // Main entry point.
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          public void Page_Loaded(object o, EventArgs e)
          {
              // Initialize the game
              Init();
          }
  
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          // Init()
          //
          // Initialize the game
          //\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//\\//
          public void Init()
          {
              // Grab reference to main canvas
              rootCanvas = (Canvas)FindName("LayoutRoot");
  
              // Setup game info
              GameInfo.Get().HostCanvas = rootCanvas;
              GameInfo.Get().stateManager = stateManager;

          }

   

  Now you can reference the game info anywhere ( as long as it's in the same namespace of course ) like so:

  GameInfo.Get().HostCanvas

  or

  GameInfo.Get().SCREEN_WIDTH

  etc.

  Hope that helps!

  - Bryan 

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  johnnystock

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  Re: Question about FindName

  Mar 14, 2008 05:22 PM | LINK

  Thanks a ton, that looks like a similar construct will help me out.  What was throwing me was not having to explicitly scope the object (can you tell I'm an ASP.NET guy?).

  John Stockton
  Microsoft Silverlight MVP and RIA Developer at Ascentium
  Co-Author of Silverlight 2 in Action