IOS UIView的生命周期的实例详解

时间:2022-09-20 12:14:00

IOS UIView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

?
1
2
3
4
5
#import <UIKit/UIKit.h>
 
@interface LifeView : UIView
 
@end
?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
#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

?
1
2
3
4
5
6
7
8
9
10
11
- (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:

?
1
2
3
4
5
6
7
// 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:

?
1
2
3
4
5
6
// 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。

如有疑问请留言或者到本站社区交流讨论,感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!

原文链接:http://blog.csdn.net/potato512/article/details/73315545