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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