Check if a view controller is visible

Check UIViewController Visibility

/* 
 * Check http://stackoverflow.com/questions/2777438/how-to-tell-if-uiviewcontrollers-view-is-visible
 * to see the discussions.
 * If the container is a UINavigationController, 
 * we can use the visibleViewController property
 * to check the visibility.
 */
navigationController visibleViewController == self

/* Or, we can add a category to UIViewController
 * to check it.
 */

@interface UIViewController (CategoryName)
-(BOOL) isVisible;
@end

@implementation UIViewController (CategoryName)
-(BOOL) isVisible {
    return [self isViewLoaded] && self.view.window;
}
@end