iOS引用计数器详细测试

本文最后更新于：2 年前

一、MRC模式

  1. 局部变量
  • ARC模式下局部变量alloc后计数器+1，release后计数器-1，计数器变为0后，对象立即被释放
  • addSubview方法也是强引用，计数器+1，所以在控制器释放后，内部的subviews计数器-1，此时计数器变为0的才会被正确释放
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- (IBAction)clickButton:(id)sender {
    AObject *aObject = [[AObject alloc] init];
    NSLog(@"retainCount = %ld", aObject.retainCount);
    [aObject release];
    
    BView *bView = [[BView alloc] init];
    NSLog(@"retainCount = %ld", bView.retainCount);
    [self.view addSubview:bView];
    NSLog(@"retainCount = %ld", bView.retainCount);
    [bView release];
    NSLog(@"retainCount = %ld", bView.retainCount);
    NSLog(@"clickButton");
}
- (void)dealloc {
    [super dealloc];
    NSLog(@"AViewController dealloc");
}

2018-08-30 14:12:06.863748+0800 testram[6748:354224] retainCount = 1
2018-08-30 14:12:06.863935+0800 testram[6748:354224] AObject dealloc
2018-08-30 14:12:06.864148+0800 testram[6748:354224] retainCount = 1
2018-08-30 14:12:06.864393+0800 testram[6748:354224] retainCount = 2
2018-08-30 14:12:06.864472+0800 testram[6748:354224] retainCount = 1
2018-08-30 14:12:06.864560+0800 testram[6748:354224] clickButton
2018-08-30 14:12:11.896023+0800 testram[6748:354224] AViewController dealloc
2018-08-30 14:12:11.896327+0800 testram[6748:354224] BView dealloc
  1. 全局变量
  • ARC模式下，只有先创建局部变量，再使用属性直接赋值，此时引用计数器才会正确累加，如果使用self点语法进行初始化，那么会受到ARC的retain和strong修饰词的影响
  • addSubview的也会使计数器+1，所以在控制器释放后，添加的subViews计数器-1，此时为0的view才会释放
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@interface AViewController ()
@property (nonatomic, strong) AObject *aObject;
@property (nonatomic, strong) BView *bView;
@end

@implementation AViewController

- (IBAction)clickButton:(id)sender {
    self.aObject = [[AObject alloc] init];
    NSLog(@"retainCount = %ld", self.aObject.retainCount);
    [self.aObject release];
    NSLog(@"retainCount = %ld", self.aObject.retainCount);
    
    BView *bView = [[BView alloc] init];
    _bView = bView;
    NSLog(@"retainCount = %ld", bView.retainCount);
    [self.view addSubview:bView];
    NSLog(@"retainCount = %ld", bView.retainCount);
    [bView release];
    NSLog(@"retainCount = %ld", bView.retainCount);
    NSLog(@"clickButton");
}

- (void)dealloc {
    [super dealloc];
    NSLog(@"AViewController dealloc");
}
@end

2018-08-30 14:16:16.162771+0800 testram[6779:360385] retainCount = 2
2018-08-30 14:16:16.162931+0800 testram[6779:360385] retainCount = 1
2018-08-30 14:16:16.163164+0800 testram[6779:360385] retainCount = 1
2018-08-30 14:16:16.163423+0800 testram[6779:360385] retainCount = 2
2018-08-30 14:16:16.163524+0800 testram[6779:360385] retainCount = 1
2018-08-30 14:16:16.163622+0800 testram[6779:360385] clickButton
2018-08-30 14:16:54.180754+0800 testram[6779:360385] AViewController dealloc
2018-08-30 14:16:54.181212+0800 testram[6779:360385] BView dealloc

二、ARC模式

  1. 局部变量
  • 在ARC模式下，系统对局部变量的自动回收是以方法为界限的，当方法执行完毕后，即开始回收局部变量
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- (IBAction)clickButton:(id)sender {
    NSLog(@"start");
    AObject *aObject = [[AObject alloc] init];
    BView *bView = [[BView alloc] init];
    NSLog(@"clickButton");
}

- (void)dealloc {
    NSLog(@"AViewController dealloc");
}

2018-08-30 11:06:48.769565+0800 testram[6184:253141] start
2018-08-30 11:06:48.769851+0800 testram[6184:253141] clickButton
2018-08-30 11:06:48.769980+0800 testram[6184:253141] BView dealloc
2018-08-30 11:06:48.770490+0800 testram[6184:253141] AObject dealloc
2018-08-30 11:06:54.061334+0800 testram[6184:253141] AViewController dealloc
  1. 全局变量
  • 在ARC模式下，系统推荐我们使用strong修饰一般属性对象，而且对点语法进行了兼容，所以可以直接使用strong的点语法进行初始化赋值
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@interface AViewController ()
@property (nonatomic, strong) AObject *aObject;
@property (nonatomic, strong) BView *bView;
@end

@implementation AViewController

- (IBAction)clickButton:(id)sender {
    NSLog(@"start");
    self.aObject = [[AObject alloc] init];
    self.bView = [[BView alloc] init];
    [self.view addSubview:self.bView];
    NSLog(@"clickButton");
}

- (void)dealloc {
    NSLog(@"AViewController dealloc");
}

@end

2018-08-30 13:49:36.579188+0800 testram[6559:324193] start
2018-08-30 13:49:36.579550+0800 testram[6559:324193] clickButton
2018-08-30 13:49:39.892344+0800 testram[6559:324193] AViewController dealloc
2018-08-30 13:49:39.892746+0800 testram[6559:324193] AObject dealloc
2018-08-30 13:49:39.893146+0800 testram[6559:324193] BView dealloc