Introduction to View Controllers

View controllers are the backbone of an iOS application. For any given screen of an iPhone, there is generally one view controller. The view controller is responsible for creating the view that is displayed on the screen, as well as handling events and firing network requests associated with that screen.

For example, in the 3 Instagram tabs shown below, each is implemented using a separate view controller. Each view controller in an app is designed and implemented separately from other view controllers. The view controllers below might be called HomeViewController, TrendingViewController, and NewsViewController.

    

Creating Custom View Controllers

Step 1: Creating a view controller

To create a new view controller, click on File->New->File. You should name the view controller related to the content of the view controller. For example, a Twitter application might have a TimelineViewController, a UserViewController, and a SettingsViewController.

If you are not using Storyboard, make sure that "With XIB for user interface" is checked. If you are using Storyboard, make sure that it is unchecked. If you've accidentally checked it, you can always delete the .xib file afterwards.

Step 2: Organizing within groups

In XCode, the folder structure within your project directory doesn't matter. Instead, you organize your files using "Groups" within XCode. Use the Command key (⌘) to select multiple files.

View Controller Lifecycle Methods

When a view controller is presented, the framework calls a series of lifecycle methods defined in the view controller.

@interface MyViewController : UIViewController

@end

@implementation MyViewController

- (void)loadView {
   // If you want to create your view programatically, implement this method.
}

- (void)viewDidLoad {
   [super viewDidLoad];

   // After the view is created successfully from the nib, this method is called.
   // This is a good place to configure your view, add gesture recognizers, add dynamics, etc.
}

- (void)viewWillAppear:(BOOL)animated {
   [super viewWillAppear:animated];

   // This method is called right before the view animates in.
}

- (void)viewDidAppear:(BOOL)animated {
   [super viewDidAppear:animated];

   // This method is called right after the transition animation finishes
}

- (void)viewWillDisappear:(BOOL)animated {
   [super viewWillDisappear:animated];

   // This method is called right before the view transitions off screen
}

- (void)viewDidDisappear:(BOOL)animated {
   [super viewDidDisappear:animated];

   // This method is called right after the exit transition animation finishes
}

References

• View Controller Programming Guide