所謂的生命周期，也就是幾個函數的調用順序，這裡以用Storyboard來創建一個ViewController為例

然後我們測試如下代碼

 

//
//  ViewController.m
//
//  Created by huangwenchen on 14/12/26.
//  Copyright (c) 2014年 huangwenchen. All rights reserved.
//

#import ViewController.h

@interface ViewController ()

@end

@implementation ViewController

- (id)initWithCoder:(NSCoder *)aDecoder{
    if (self = [super initWithCoder:aDecoder]) {
        NSLog(@initWithCoder Called);
    }
    return self;
}
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@viewDidLoad Called);
    // Do any additional setup after loading the view, typically from a nib.
    
}
- (void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear:animated];
    NSLog(@viewWillAppear Called);
}

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

}

-(void)awakeFromNib{
    NSLog(@awakeFromNib Called);
}

-(void)viewWillLayoutSubviews{
    NSLog(@viewWillLayoutSubviews Called);
}
-(void)viewDidLayoutSubviews{
    NSLog(@viewDidLayoutSubviews Called);
}

@end

然後，在模擬器上運行，輸出為

 

2014-12-29 19:42:47.904 KVCForCSDN[2370:126741] initWithCoder Called
2014-12-29 19:42:47.907 KVCForCSDN[2370:126741] awakeFromNib Called
2014-12-29 19:42:47.927 KVCForCSDN[2370:126741] viewDidLoad Called
2014-12-29 19:42:47.927 KVCForCSDN[2370:126741] viewWillAppear Called
2014-12-29 19:42:47.961 KVCForCSDN[2370:126741] viewWillLayoutSubviews Called
2014-12-29 19:42:47.963 KVCForCSDN[2370:126741] viewDidLayoutSubviews Called
2014-12-29 19:42:47.970 KVCForCSDN[2370:126741] viewDidAppear Called

 

所以，調用順序為

1 init函數(init;initWithFrame;initWithCoder;等)－－初始化

2 awakeFromNib－－在loadView之前的工作放在這裡

3 viewDidLoad－－注意，一個ViewController一個生命周期內這個函數只會調用一次

4 viewWillAppear －－ view將要出現，每次View消失再出現都會調用

5 viewWillLayoutSubviews－－簡要對子試圖進行布局

6 viewDidLayoutSubivews－－完成對子試圖布局

7 viewDidAppear－－視圖將要出現在屏幕上

－－－上述代碼不含部分

8 viewWillDisappear－－View將要消失

9 viewDidDisappear－－View已經消失

這九個就是通常的視圖控制器生命周期內函數調用順序，一定要清楚什麼樣的代碼應該放在視圖控制器生命周期的什麼位置

BTY：

 

didReceiveMemoryWarning

這個函數通常也在生命周期的考慮范圍內，當內存不足時候會調用，這時候應當進行適當的內存釋放，不然IOS會強制關閉當前的APP