title: Why is GLKView's DrawableWidth not set in ViewDidLoad?
body: <p>I'm using GLKit's GLKViewController/GLKView to do some basic OpenGL drawing.</p>
  
  <p>I'd like to setup the ViewPort in the ViewDidLoad method. After reading the GLKView reference, I thought I'd be able to do it like this:</p>
  
  <pre><code>- (void)viewDidLoad
  {
      [super viewDidLoad];
      self.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
      if (!self.context) {
          NSLog(@"Failed to create ES context");
      }
      GLKView *view = (GLKView *)self.view;
      view.context = self.context;
      glViewport( 0, 0, view.DrawableWidth, view.DrawableHeight );
  }
  </code></pre>
  
  <p>The problem is that both <code>DrawableWidth</code> and <code>DrawableHeight</code> properties are zero. Why is that? When the GLKView calls DrawInRect, they're set and their values are what I would expect.</p>