title: [iOS]: detect when view controller appears after back from another external app
body: <p>This is my escenario: </p>
  
  <p>I have a view controller where the user can go to another application (Settings) when push a button in this way:</p>
  
  <pre><code>    -(void) goToSettings{
         [[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];
      }
  </code></pre>
  
  <p>So, this code open the app's screen settings and it shows in the upper left corner a legend like this:</p>
  
  <blockquote>
    <p>Back to myApplication</p>
  </blockquote>
  
  <p>I wish to detect when the view controller where user push the button is active again. I know you can detect when app is active again with this method in the delegate file</p>
  
  <pre><code>- (void)applicationWillEnterForeground:(UIApplication *)application
  </code></pre>
  
  <p>But I need detect in specific the view controller. I have tried with <code>-(void)viewWillAppear:(BOOL)animated</code> but It not works. Anyone have any idea about this?</p>