UIViewController的生命周期

前言

UIViewController的生命周期函數(shù):

• init(initWithNibName) 初始化
• loadView 加載自定義的視圖(如果是從xib文件加載, 通常不需要添加此方法; 如果添加該方法, 系統(tǒng)則不會自動創(chuàng)建根view)
• viewDidLoad 視圖加載完成, 可以進行布局,創(chuàng)建其他控件和獲取數(shù)據(jù)
• viewWillAppear 視圖即將出現(xiàn)
• viewDidAppear 視圖已經(jīng)顯示完成
• viewWillDisappear 視圖即將消失
• viewDidDisappear 視圖已經(jīng)消失
• viewWillLayoutSubviews 在view的layoutSubviews方法執(zhí)行前調(diào)用
• viewDidLayoutSubviews 在view的layoutSubviews方法執(zhí)行后調(diào)用
• didReceiveMemoryWarning 系統(tǒng)內(nèi)存警告
• dealloc 銷毀視圖

創(chuàng)建視圖

從xib加載:
init-> viewDidLoad-> viewWillAppear-> viewDidAppear

從自定義視圖加載:

init-> loadView -> viewDidLoad-> viewWillAppear->viewWillLayoutSubviews->(view)layoutSubviews -> viewDidLayoutSubviews -> viewDidAppear

代碼:

//ThirdView.m

@implementation ThirdView
- (void)layoutSubviews {
    [super layoutSubviews];
    NSLog(@"ThirdView layoutSubviews");
}
@end

//ThirdViewController.m

@implementation ThirdViewController
- (id)init {
    if (self = [super init]) {
        NSLog(@"ThirdViewController init");
        return self;
    }
    return nil;
}
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"ThirdViewController viewDidLoad");

}

- (void)loadView {
    NSLog(@"ThirdViewController loadView");
    ThirdView *view = [ThirdView new];
    self.view = view;
}

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"ThirdViewController viewWillAppear");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"ThirdViewController viewDidAppear");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"ThirdViewController viewDidDisappear");
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"ThirdViewController viewWillDisappear");
}

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    NSLog(@"ThirdViewController viewWillLayoutSubviews");

}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    NSLog(@"ThirdViewController viewDidLayoutSubviews");
}
@end

輸出:

2018-08-09 20:16:01.577931+0800 LifeCycle[42337:3300297] ThirdViewController init
2018-08-09 20:16:01.581844+0800 LifeCycle[42337:3300297] ThirdViewController loadView
2018-08-09 20:16:01.582142+0800 LifeCycle[42337:3300297] ThirdViewController viewDidLoad
2018-08-09 20:16:01.582462+0800 LifeCycle[42337:3300297] ThirdViewController viewWillAppear
2018-08-09 20:16:01.611263+0800 LifeCycle[42337:3300297] ThirdViewController viewWillLayoutSubviews
2018-08-09 20:16:01.611392+0800 LifeCycle[42337:3300297] ThirdView layoutSubviews
2018-08-09 20:16:01.611473+0800 LifeCycle[42337:3300297] ThirdViewController viewDidLayoutSubviews
2018-08-09 20:16:02.114443+0800 LifeCycle[42337:3300297] ThirdViewController viewDidAppear

視圖顯示邏輯

Controller之間的顯示隱藏邏輯
代碼:

//ViewController.m

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"ViewController viewWillAppear");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"ViewController viewDidAppear");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"ViewController viewDidDisappear");

}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"ViewController viewWillDisappear");
}

//SecondViewController.m

@implementation SecondViewController

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

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    NSLog(@"SecondViewController viewWillAppear");
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    NSLog(@"SecondViewController viewDidAppear");
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    NSLog(@"SecondViewController viewDidDisappear");
    
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    NSLog(@"SecondViewController viewWillDisappear");
}

@end

ViewController push SecondViewController輸出:

2018-08-09 20:20:52.184795+0800 LifeCycle[42496:3307472] ViewController viewWillDisappear
2018-08-09 20:20:52.184965+0800 LifeCycle[42496:3307472] SecondViewController viewWillAppear
2018-08-09 20:20:52.711445+0800 LifeCycle[42496:3307472] ViewController viewDidDisappear
2018-08-09 20:20:52.711620+0800 LifeCycle[42496:3307472] SecondViewController viewDidAppear

SecondViewController pop back to ViewController輸出:

2018-08-09 20:23:37.193745+0800 LifeCycle[42496:3307472] SecondViewController viewWillDisappear
2018-08-09 20:23:37.193930+0800 LifeCycle[42496:3307472] ViewController viewWillAppear
2018-08-09 20:23:37.698928+0800 LifeCycle[42496:3307472] SecondViewController viewDidDisappear
2018-08-09 20:23:37.699078+0800 LifeCycle[42496:3307472] ViewController viewDidAppear

總結(jié):

頁面間push的顯示邏輯總是先觸發(fā)Disappear, 然后觸發(fā)Appear

其他

• 收到didReceiveMemoryWarning方法調(diào)用時,嗎我們需要把不是位于頂級視圖的view全部釋放掉(有些業(yè)務(wù)上必須留存的視圖除外), 以減輕內(nèi)存壓力; 恢復(fù)頁面時, Controller會重新走loadView流程, 此時需要注意業(yè)務(wù)邏輯是否重復(fù)

• 除了init方法, 其他方法在生命周期內(nèi)都可能多以調(diào)用

• loadView 實現(xiàn)該方法, 卻沒有給self.view賦值的情況下, 不會產(chǎn)生根view

demo地址