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
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#import <UIKit/UIKit.h>
@interface LifeView : UIView
@end
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#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
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其次，在B视图控制器中实例化，并添加到父视图
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- (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];
}
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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：
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// 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-->
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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：
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// 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-->
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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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原文链接：http://blog.csdn.net/potato512/article/details/73315545