title: Objective-C existing instance variable must be __unsafe_unretained error
body: <p>Same code are already questionned here, but I deal with a different problem that I can't solve myself probably because i'm new with Objective-C, so I decide to ask the question :)</p>
  
  <p>webberAppDelegate.h:</p>
  
  <pre><code>#import &lt;Cocoa/Cocoa.h&gt;
  #import &lt;WebKit/WebKit.h&gt;
  
  @interface webberAppDelegate : NSObject &lt;NSApplicationDelegate&gt; {
      NSWindow *window;
      WebView *webber;
  }
  
  @property (assign) IBOutlet NSWindow *window;
  @property (assign) IBOutlet WebView *webber;
  
  @end
  </code></pre>
  
  <p>webberAppDelegate.m:</p>
  
  <pre><code>#import "webberAppDelegate.h"
  
  @implementation webberAppDelegate
  
  @synthesize window;
  @synthesize webber;
  
  - (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
      NSString *urlString = @"http://www.apple.com";
      // Insert code here to initialize your application
      [[webber mainFrame] loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:urlString]]];
  }
  
  @end
  </code></pre>
  
  <p>So, in webberAppDelegate.m, here's my problem with this fraction I suppose:</p>
  
  <pre><code>  @synthesize window;
    @synthesize webber;
  </code></pre>
  
  <p>who give me this long error:</p>
  
  <pre><code>Existing instance variable 'window' for property 'window' with  assign attribute must be __unsafe_unretained
  </code></pre>
  
  <p>and pratically the same for other var "webber":</p>
  
  <pre><code>Existing instance variable 'webber' for property 'webber' with  assign attribute must be __unsafe_unretained
  </code></pre>
  
  <p>Thanks for your help, I really appreciate Stackoverflow community for days !!</p>