ios中的循环引用

• 在ios中使用block (闭包) 的时候,代码块中使用到self 有可能出现循环引用

• 循环引用的两种形式:

  • 多个对象循环强引用,都不能释放,导致内存泄露
  • 单例强引用其他对象,由于单例不会被释放销毁,程序结束时才会销毁,导致其他对象不能及时销毁

OC中的循环引用

• 建立NetworkTools类

@interface NetworkTools ()@property (nonatomic, strong) void(^finishedBlock)();@end@implementation NetworkTools- (void)loadDataWithFinishBlock:(void (^)())finishBlock {    self.finishedBlock = finishBlock;    [self work];}- (void)work {   if (self.finishedBlock) {        self.finishedBlock();    }}- (void)dealloc {    NSLog(@"%@  dealloc",self);}@end

• 示例化NetworkTools并加载数据

@interface ViewController ()@property (nonatomic, strong) NetworkTools *networkTools;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];    self.networkTools = [NetworkTools new];    [self.networkTools loadDataWithFinishBlock:^(){        NSLog(@"%@",self.view);    }];}- (void)dealloc {    NSLog(@"%@  dealloc",self);}@end

运行测试会出现循环引用

• 原因:
  
  • viewController ==> networkTools ==> finishedBlock ==> self(viewController)
  • ==> 表示强引用

解除循环引用

• 使用__weak typeof(self) weakSelf = self;

  • 如果self 被释放,weakSelf 的地址将改为nil

- (void)viewDidLoad {    [super viewDidLoad];    self.networkTools = [NetworkTools new];    __weak typeof(self) weakSelf = self;    [self.networkTools loadDataWithFinishBlock:^(){        NSLog(@"%@",weakSelf.view);    }];}

• 使用 __unsafe_unretained typeof(self) weakSelf = self;
  
  • weakSelf 是assign,当self被释放时,weakSelf 的地址不会改变,可能会出现野指针错误

- (void)viewDidLoad {    [super viewDidLoad];    self.networkTools = [NetworkTools new];    __unsafe_unretained typeof(self) weakSelf = self;    [self.networkTools loadDataWithFinishBlock:^(){        NSLog(@"%@",weakSelf.view);    }];}

• 推荐使用 __weak 的方式解决OC中的循环引用

swift 中的循环引用

• 建立NetworkTools类

class NetworkTools1: NSObject {    var finishedCallBack: (() -> ())?    func loadData(finishedCallBack: () -> ()) {        dispatch_async(dispatch_get_global_queue(0, 0)) { () -> Void in            print("加载数据")            NSThread.sleepForTimeInterval(2)            self.finishedCallBack = finishedCallBack;            self.work()        }    }    func work() {        finishedCallBack?()    }    deinit {        print("\(self) deinit")    }}

• 示例化NetworkTools并加载数据

class ViewController1: UIViewController {    var networkTools: NetworkTools1?    override func viewDidLoad() {        super.viewDidLoad()        networkTools = NetworkTools1()        networkTools?.loadData({ () -> () in            print("\(self.view)")        })    }    deinit {        print("\(self) deinit")    }}

运行测试会出现循环引用

• 原因:
  
  • ViewController1 ==> networkTools ==> finishedCallBack ==> self(ViewController1)

解除循环引用

• 使用weak
  
  • 当self释放时,weakSelf为变为 nil

 weak var weakSelf = self        networkTools?.loadData({ () -> () in            print("\(weakSelf?.view)")        })

• 使用 [weak self]
  
  • 闭包中的self是可选项,当self 被释放时,self? 不执行,更安全

networkTools?.loadData({[weak self] () -> () in            print("\(self?.view)")        })

• 使用 [unowned self]
  
  • self 不是可选项,如果self 已经被释放,则会出现野指针错误

 networkTools?.loadData({[unowned self] () -> () in            print("\(self.view)")        })

• swift 中推荐使用 [weak self] 解决循环引用