title: Error "_OBJC_CLASS_$_AppDelegate", referenced from:" and error: linker command failed with exit code 1 (use -v to see invocation)"
body: <p>I'm pretty new to developing, and i got this error, I'm not shire if i got something missing in my AppDelegate files so I'm gonna show you the files.</p>
  
  <p><strong>the h-file</strong></p>
  
  <pre><code>#import &lt;UIKit/UIKit.h&gt;
  
  
  @interface AppDelegate: UIResponder &lt;UIApplicationDelegate&gt;
  
  
  @property (strong, nonatomic)  UIWindow *window;
  
  @end
  </code></pre>
  
  <p><strong>the m-file</strong></p>
  
  <pre><code>#import "AppDelegate.h"
  </code></pre>
  
  <p>the thing is that i think i removed something from te m-file but i can't remember what it was</p>
  
  <p>here is the full error message:</p>
  
  <p><strong>Undefined symbols for architecture x86_64:
    "_OBJC_CLASS_$_AppDelegate", referenced from:
        objc-class-ref in main.o
  ld: symbol(s) not found for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)</strong></p>