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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