title: The PickView is not visible when I run iPhone simulator
body: <p>I drag a <code>PickerView</code> and a button to the View in my xib file. </p>
  
  <p>But, when I build my code, only my button shows in the simulator. It seems that the <code>PickerView</code> has been hidden because I have got the data from the <code>PickerView</code>.</p>
  
  <p>What is the reason for this problem? How can I fix it?</p>