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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