title: Why is NSViewController not binding representedObject?
body: <p>In short: I bind an <code>NSTextField</code> to the File's Owner (the view controller) and Model Key Path of <code>representedObject.firstName</code>, but editing the text field does not change the <code>firstName</code>. </p>
  
  <p>Here are more details. I have a simple program that does nothing but create an instance of <code>Thing</code> (a simple class with some properties), and <code>ThingViewController</code>.  The controller has an associated <code>.xib</code> with a simple UI -- a couple text fields to bind to properties of the <code>Thing</code>.</p>
  
  <pre><code>@interface Thing : NSObject
  @property (nonatomic, strong) NSString *firstName;
  @property (nonatomic, strong) NSString *lastName;
  @property (nonatomic) BOOL someBool;
  @end
  </code></pre>
  
  <p>And in the app delegate...</p>
  
  <pre><code>- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
  {
      NSView *cv = self.window.contentView;
      ThingViewController *vc = [[ThingViewController alloc] 
                                   initWithNibName:@"ThingViewController" bundle:nil];
      theThing = [Thing new];
      theThing.firstName = @"Rob";
      vc.representedObject = theThing;   
      [cv addSubview:vc.view];
  }
  </code></pre>
  
  <p>The <code>ThingViewController.xib</code> is simple:</p>
  
  <p><img src="https://i.stack.imgur.com/k1LGr.png" alt="enter image description here">    </p>
  
  <p>And here is the binding for that first text field:</p>
  
  <p><img src="https://i.stack.imgur.com/8pBKR.png" alt="enter image description here"></p>
  
  <p>When I run, the text field does show "Rob", so it works in that direction, but then as I edit the text field, the <code>firstName</code> property of <code>theThing</code> does not change.</p>
  
  <p>What am I doing wrong?</p>
  
  <p><strong>Edit</strong>: Here's a link to a zipped project file for the above code: <a href="https://drive.google.com/file/d/0B2NHW8y0ZrBwWjNzbGszaDQzQ1U/edit?usp=sharing" rel="nofollow noreferrer">https://drive.google.com/file/d/0B2NHW8y0ZrBwWjNzbGszaDQzQ1U/edit?usp=sharing</a></p>