CODEWITHSUNDEEP
ios
Scott
Scott

Reputation: 162

viewDidLoad and loadView questions

I want to test the difference between viewDidLoad and loadView ,so i create a single view application and than set the didFinishLaunchingWithOptions as flows:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    viewController = [[MyViewController alloc] init];
//    viewController.view.backgroundColor = [UIColor redColor];
    self.window.rootViewController = viewController;
    [self.window makeKeyAndVisible];
    return YES;
}

In my MyViewController's m file is as flows:

#import "MyViewController.h"

@interface MyViewController ()

@end

@implementation MyViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"%@",self.view);
    self.view.backgroundColor = [UIColor redColor];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)loadView {
    self.view = [[UIWebView alloc] initWithFrame:[UIScreen mainScreen].applicationFrame];
}

@end

But the loadView method or viewDidLoad are not called.Why? But when i cancel the annotation at the didFinishLaunchingWithOptions .they all are called.

Upvotes: 0

Views: 110

Answers (3)

Bannings
Bannings

Reputation: 10479

Why the viewDidLoad is not called?

This behavior happens because your window is a nil. So your controller have not displayed and its view is not loaded.

Try this:

self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
ViewController *viewController = [[ViewController alloc] init];
//    viewController.view.backgroundColor = [UIColor redColor];
self.window.rootViewController = viewController;
[self.window makeKeyAndVisible];

Why the viewDidLoad is called if uncommented this line viewController.view.backgroundColor = [UIColor redColor];?

A view of an UIViewController is lazy loading. If you cancel the annotation at the didFinishLaunchingWithOptions, although your controller have not displayed, but you have visit its view property then the view will to be loaded then going to be discarded.

Upvotes: 1

Kevin
Kevin

Reputation: 1157

"loadView" is called when self.view is called and self.view is nil, so if you uncomment 

viewController.view.backgroundColor = [UIColor redColor];

you literally call self.view, it would then call(internally) "loadView" and then "viewDidLoad".

I guess it is because "self.window" is not initialised, "loadView" and "viewDidLoad" are not called.

Upvotes: 1

John Tracid
John Tracid

Reputation: 4046

I just checked with simple example:

@implementation TestViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"test");
}

- (void)loadView
{
    NSLog(@"load");
}

@end

And it works fine:

2015-08-16 13:18:46.163 Example[51603:406197] load
2015-08-16 13:18:46.164 Example[51603:406197] test
2015-08-16 13:18:46.164 Example[51603:406197] load
2015-08-16 13:18:46.164 Example[51603:406197] test

Here is delegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{
    self.window.rootViewController = [TestViewController new];
    [self.window makeKeyAndVisible];
    return YES;
}

Update #1

I forgot about default storyboard I have. I don't use it but it is required for window property initialisation in delegate:

Implementation of this property is required if your app’s Info.plist file contains the UIMainStoryboardFile key. Fortunately, the Xcode project templates usually include a synthesized declaration of the property automatically for the app delegate. The default value of this synthesized property is nil, which causes the app to create a generic UIWindow object and assign it to the property. If you want to provide a custom window for your app, you must implement the getter method of this property and use it to create and return your custom window.

Upvotes: 1

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