UIViewController的生命周期比較簡(jiǎn)單，整個(gè)流程調(diào)用代碼順序如下:

1. initWithNibName:bundle: 初始化UIViewController痹束，執(zhí)行關(guān)鍵數(shù)據(jù)初始化操作张症，非StoryBoard創(chuàng)建UIViewController都會(huì)調(diào)用這個(gè)方法.

2. initWithCoder: 如果通過(guò)StoryBoard進(jìn)行視圖管理仓技，程序不會(huì)直接初始化一個(gè)UIViewController，StoryBoard會(huì)自動(dòng)初始化或在segue被觸發(fā)時(shí)自動(dòng)初始化吠冤，因此方法initWithNibName:bundle不會(huì)被調(diào)用浑彰，但是initWithCoder會(huì)被調(diào)用。

3. loadView :當(dāng)訪問(wèn)UIViewController的View屬性時(shí)拯辙，View如果此時(shí)為nil,那么ViewController會(huì)自動(dòng)調(diào)用loadView方法來(lái)初始化一個(gè)UIView并賦值給UIViewController的View郭变；如果沒(méi)有重載lodaView方法，則UIViewController會(huì)從nib或StoryBoard中查找默認(rèn)的loadView涯保，默認(rèn)的loadView會(huì)返回一個(gè)空白的UIView對(duì)象.

4. viewDidLoad:當(dāng)loadView將view載入內(nèi)存中诉濒，可以對(duì)加載網(wǎng)絡(luò)數(shù)據(jù)，視圖的UI初始化.

5. viewWillAppear:系統(tǒng)在載入所有的數(shù)據(jù)后夕春，在視圖展示之前還可以進(jìn)行進(jìn)一步的調(diào)整(比如設(shè)置狀態(tài)欄方向).

6. viewWillLayoutSubviews:view 即將布局其Subviews.

7. viewDidLayoutSubviews:view已經(jīng)布局其Subviews.

8. viewDidAppear:視圖完全展示在界面之前最后的調(diào)整.

9. viewWillDisappear:在視圖切換是未荒，當(dāng)前視圖在即將被移除、或被覆蓋是及志，此時(shí)還沒(méi)有調(diào)用removeFromSuperview片排。

10. viewDidDisappear:view已經(jīng)消失或被覆蓋寨腔，此時(shí)已經(jīng)調(diào)用removeFromSuperView;

11. dealloc:視圖被銷(xiāo)毀.

12. didReceiveMemoryWarning:在內(nèi)存足夠的情況下，app的視圖通常會(huì)一直保存在內(nèi)存中率寡，但是如果內(nèi)存不夠迫卢，一些沒(méi)有正在顯示的viewController就會(huì)收到內(nèi)存不夠的警告，然后就會(huì)釋放自己擁有的視圖冶共，以達(dá)到釋放內(nèi)存的目的乾蛤。但是系統(tǒng)只會(huì)釋放內(nèi)存，并不會(huì)釋放對(duì)象的所有權(quán)捅僵，所以通常我們需要在這里將不需要顯示在內(nèi)存中保留的對(duì)象釋放它的所有權(quán)家卖，將其指針置nil。

- (instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    
    if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
        NSLog(@"FlyElephant---%s", __FUNCTION__);
    }
    return self;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder {
    NSLog(@"FlyElephant---%s", __FUNCTION__);
    if (self = [super initWithCoder:aDecoder]) {
        NSLog(@"FlyElephant---%s", __FUNCTION__);
    }
    return self;
}

- (void)loadView {
    [super loadView];
    NSLog(@"FlyElephant---%s", __FUNCTION__);
    self.view = [[UIView alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.view.backgroundColor = [UIColor greenColor];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)viewDidAppear:(BOOL)animated {
    NSLog(@"%s", __FUNCTION__);
    [super viewDidAppear:animated];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    NSLog(@"FlyElephant--%s", __FUNCTION__);
}

- (void)dealloc {
    NSLog(@"%s", __FUNCTION__);
}

非StoryBoard中控制器加載過(guò)程:

FlyElephant.png

StoryBoard中控制器加載過(guò)程:

FlyElephant.png