Road To iOS Series 7

View Controller Essentials :

• An instance of a subclass of UIViewController
• It manages a view hierarchy
• It’s responsible for creating view objects, handling events

View in View Controller :

• It’s the root of view controller’s view hierarchy
• Two ways of creating its view hierarchy :
  • Programmatically, override the UIViewController method loadView
  • Interface Builder, loading a NIB file

Create view programmatically :

In your own view controller class(which can be created by inheriting UIViewController), override the loadview:

- (void)loadView
{
	// 1. specify the view's frame
	// could use other Rect like full screen
	// [UIScreen mainScreen].bounds
	CGRect firstFrame = CGRectMake(160, 200, 100, 105);

	// 2. init an instance of view
	YourOwnView *firstView = [[YourOwnView alloc] initWithFrame:firstFrame];

	// 3. configure the  view
	firstView.backgroundColor = [UIColor greenColor];

	// 4. set the view in view controller to this view
	// sometimes you use addSubView if you have multiple views
	// e.g. [firstView addSubview: secondView];
	self.view = firstView;
}

However, the code above is for creating view hierarchy in view controller only, it has nothing to do with the actual view appeared on the screen. To connect a view in view controller with screen, you need to use UIwindow’s setRootViewController.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
	self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

	// init your view controller
	YourOwnViewController *vc = [YourOwnViewController alloc] init];

	// set the window's root controller
	self.window.rootViewController = vc;

	self.window.backgroundColor = [UIColor whiteColor];
	[self.window makeKeyAndVisible];
	return YES;
}

Create view use XIB :

• Steps for creating view for view controller using XIB:
  • create a view using interface builder(i.e. create xib file)
  • create your view controller for this xib
  • make sure your xib’s name is named the same as your view controller (xcode uses this to automatically load nib file i.e. init the view)
  • connect your controller to your xib(e.g. File’s owner, IBOutlet, IBAction)

@interface YourOwnViewController ()

// IBOutlet is typedef as void, it's only for xcode to identify the specific element in xib
// Pay attention to the weak decorator, follow parent-child rule
@property (nonatomic, weak) IBOutlet UIDatePicker *datePicker;

@end

// IBAction is typedef as void, it's only for xcode to identify the specific action in xib
- (IBAction)addReminder:(id)sender
{
    NSDate *date = self.datePicker.date;
    NSLog(@"Setting a reminder for %@", date);
}

After you get your xib and view controller done, you may now connect these two together.

• Connect to File’s Owner in xib
  • use identity inspector to change the view controller class to your own class
• Connect outlet and actions
  • right click on File’s Owner, drag-and-drop those connections between your controller and xib

UIViewController Initializer :

• Designated Initializer: initWithName:bundle:
• Simply call alloc and init
• Sending init to a view controller calls initWithName:bundle: and passes nil for both arguments
• When a view controller is initialized with nil as its NIB name, it searches for a NIB file with the name of the class

UIViewController Lifecycle :

See previous post for more details: View Controller Lifecycle

Reference

1. Stanford iOS 7 development
2. Mac Developer Library
3. Big Nerd Ranch

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