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IOS UIView的生命周期的实例详解

来源: 网络整理  作者: 佚名

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。

Tags:周期 实例 生命
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