title: UIView drawRect issue
body: <p>I want to make custom UIView with border. Here is my code: </p>
  
  <pre><code>- (void)drawRect:(CGRect)rect
  {
      CGContextRef context = UIGraphicsGetCurrentContext();
      CGContextSetLineWidth(context, 4.0);
      CGContextSetStrokeColorWithColor(context, [[UIColor blueColor] CGColor]);
      CGContextAddRect(context, self.frame);
      CGContextStrokePath(context);
  }
  </code></pre>
  
  <p>And here is the result: <img src="https://i.stack.imgur.com/d3eUX.png" alt="enter image description here"></p>
  
  <p>All three UIView on this picture is my custom view, but only big UIView have the border. I don't understand why others have no border. What is wrong?</p>