IOS UIView的生命周期的实例详解

IOS UIView的生命周期的实例详解

任何对象的者有一个生命周期，即都存在一个实例化到销毁的过程。

UIView对象也不例外，那么UIView从init/new开始后，直到dealloc结束的过程中都经历了哪些过程呢？

首先自定义继承自UIView的对象LifeView

#import <UIKit/UIKit.h> 
 
@interface LifeView : UIView 
 
@end 

#import "LifeView.h" 
 
@interface LifeView () 
{ 
  NSInteger count; 
} 
 
@end 
 
@implementation LifeView 
 
- (instancetype)initWithFrame:(CGRect)frame 
{ 
  self = [super initWithFrame:frame]; 
  if (self) 
  { 
    NSLog(@"<-- 1 %s , count = %@-->", __func__, @(count++)); 
  } 
  return self; 
} 
 
 
- (void)willMoveToSuperview:(nullable UIView *)newSuperview 
{ 
  NSLog(@"<-- 2 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)didMoveToSuperview 
{ 
  NSLog(@"<-- 3 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)willMoveToWindow:(nullable UIWindow *)newWindow 
{ 
  NSLog(@"<-- 4/7 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)didMoveToWindow 
{ 
  NSLog(@"<-- 5/8 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)layoutSubviews 
{ 
  NSLog(@"<-- 6 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)removeFromSuperview 
{ 
  NSLog(@"<-- 9 %s , count = %@-->", __func__, @(count++)); 
} 
 
- (void)dealloc 
{ 
  NSLog(@"<-- 10 %s , count = %@-->", __func__, @(count++)); 
} 
 
@end 

其次，在B视图控制器中实例化，并添加到父视图

- (void)viewDidLoad { 
  [super viewDidLoad]; 
  // Do any additional setup after loading the view. 
   
  self.title = @"life view"; 
   
  LifeView *lifeView = [[LifeView alloc] initWithFrame:CGRectMake(10.0, 80.0, 100.0, 100.0)]; 
  [self.view addSubview:lifeView]; 
  lifeView.tag = 1000; 
  lifeView.backgroundColor = [UIColor orangeColor]; 
} 

当B视图控制器被push，或present出来时，被调用的LifeView的相关方法，如下所示：

// 实例化时 
2017-06-16 00:37:10.694 DemoViewLife[3963:121184] <-- 1 -[LifeView initWithFrame:] , count = 0--> 
2017-06-16 00:37:10.695 DemoViewLife[3963:121184] <-- 2 -[LifeView willMoveToSuperview:] , count = 1--> 
2017-06-16 00:37:10.695 DemoViewLife[3963:121184] <-- 3 -[LifeView didMoveToSuperview] , count = 2--> 
2017-06-16 00:37:10.697 DemoViewLife[3963:121184] <-- 4/7 -[LifeView willMoveToWindow:] , count = 3--> 
2017-06-16 00:37:10.697 DemoViewLife[3963:121184] <-- 5/8 -[LifeView didMoveToWindow] , count = 4--> 
2017-06-16 00:37:10.701 DemoViewLife[3963:121184] <-- 6 -[LifeView layoutSubviews] , count = 5--> 

当B视图控制器被pop，或dismiss时，被调用的LifeView的相关方法，如下所示：

// 销毁时 
2017-06-16 00:37:25.514 DemoViewLife[3963:121184] <-- 4/7 -[LifeView willMoveToWindow:] , count = 6--> 
2017-06-16 00:37:25.514 DemoViewLife[3963:121184] <-- 5/8 -[LifeView didMoveToWindow] , count = 7--> 
2017-06-16 00:37:25.515 DemoViewLife[3963:121184] <-- 9 -[LifeView removeFromSuperview] , count = 8--> 
2017-06-16 00:37:25.516 DemoViewLife[3963:121184] <-- 9 -[LifeView removeFromSuperview] , count = 9--> 
2017-06-16 00:37:25.518 DemoViewLife[3963:121184] <-- 10 -[LifeView dealloc] , count = 10--> 

从打印信息可以看到方法"removeFromSuperview"被调用了两次，这是因为在B视图控制器中，主动调用了该方法。如果没有主动调用该方法的话，只会被调用一次。

另外被执行过两次的方法还有"willMoveToWindow"和"didMoveToWindow"。我们可以很好地进行区分，当newWindow存在时，则是实例化创建被第一次调用；而当newWindow为nil时，则是被销毁了，即结束生命周期。

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