title: UIView animation doesn't work
body: <p>The codes are very basic:</p>
  
  <pre><code>UIImageView *testView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 80, 80)];
  [self.view addSubview:testView];
  [testView setImage:[UIImage imageNamed:@"button.png"]];
  [UIView animateWithDuration:100
                   animations:^{testView.center =  CGPointMake(140,350);}
                   completion:^(BOOL finished){NSLog(@"animation finished");
                   }
   ];
  </code></pre>
  
  <p>And somehow the animation just won't work. The image only shows up at the end position. The NSLog message does get displayed though.</p>
  
  <p><strong>Does anyone know what may fail an animation?</strong></p>
  
  <p>Thank you very much.</p>