title: Make variable available to entire application using AppDelegate
body: <p>I am extraordinarily confused by the concept of using the app delegate to make a variable be able to be set and used anywhere in my application.  Here's my code:</p>
  
  <p>appdelegate.h</p>
  
  <pre><code>@interface AppDelegate : UIResponder &lt;UIApplicationDelegate&gt;
  {
      NSMutableString *globalUsername;
  }
  @property (strong, nonatomic) UIWindow *window;
  @property (nonatomic, retain) NSMutableString *globalUsername;
  </code></pre>
  
  <p>appdelegate.m</p>
  
  <pre><code>@synthesize globalUsername;
  </code></pre>
  
  <p>and another view scene (called "Forum.h" where I am trying to set the value)</p>
  
  <pre><code>AppDelegate *appDelegate = (MyAppDelegate *)[[[UIApplication sharedApplication] delegate]];
  [appDelegate globalUsername appendString;
  </code></pre>
  
  <p>the last line is incomplete of course, but xcode automatically pickets up globalUsername variable, I just cannot call the "appendString" function to actually change it.  </p>