title: Can I change property UIReturnKeyType of UITextField dynamically?
body: <p>we can set this property of UITextField to "Send", "Search", "Go", etc.:</p>
  
  <pre><code>@property(nonatomic) UIReturnKeyType returnKeyType
  </code></pre>
  
  <p>But setting it while using the UITextField doesn't change at all.</p>
  
  <p>I want this behavior:
  When UITextField is empty, let returnKeyType be "Return", otherwise let returnKeyType be "Send".</p>