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block循环引用解决

实验代码

@interface ViewController () @property (nonatomic, strong) TestNetworkBlock *testNetwork; @end

@implementation ViewController

(void)viewDidLoad {

[super viewDidLoad];// Do any additional setup after loading the view, typically from a nib.self.testNetwork = [[TestNetworkBlock alloc] init];[self.testNetwork ceshi];[self.testNetwork release], self.testNetwork = nil;

}

@end

@interface TestNetworkBlock ()

{

countBlock _countBlock;

}

@property (nonatomic, strong) NSString *strTest;

@end

@implementation TestNetworkBlock

(id) init

{

self = [super init];

if (self)

{

self.strTest = @"我的测试";__weak TestNetworkBlock *weakSelf = self;_countBlock = ^(int i){    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){        sleep(5);        NSString *string = [weakSelf zhixing:i];        NSLog(@"string=====%@", string);    });};

}

return self;

}

(NSString *) zhixing:(int) i

{

NSString *string = [NSString stringWithFormat:@"%@%d", self.strTest, i];

return string;

}

(void) ceshi

{

_countBlock(5);

}(void) dealloc

{

NSLog(@"======dealloc");

}

@end

问题剖析：

多线程调用，block外面声明了weakSelf，则block内部对self的引用为指针引用，当外部[self.testNetwork release], self.testNetwork = nil;时，weakSelf为nil，所以导致运行失败。

第二种：block改为self引用

_countBlock = ^(int i){

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){            sleep(5);            NSString *string = [self zhixing:i];            NSLog(@"string=====%@", string);        });    };

问题剖析

_countBlock为self对象，self强引用了_countBlock，同时_countBlock又怕里面self释放，所以block体里面会强引用self。导致循环引用，内存一直不会被释放，dealloc也不会被调用。

正确做法：block内部加入bSelf强引用指针

__weak TestNetworkBlock *weakSelf = self; _countBlock = ^(int i){

TestNetworkBlock *bSelf = weakSelf;        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(void){            sleep(5);            NSString *string = [bSelf zhixing:i];            NSLog(@"string=====%@", string);        });    };

问题剖析

在 block 之前定义对 self 的一个弱引用 wSelf，因为是弱引用，所以当 self 被释放时 wSelf 会变为nil；

在block体内部声明一个强引用对象bself指向该wSelf。bSelf只会在block内部执行完毕才会消亡，这样就保证了self对象被外部其他线程释放掉的情况。又避免了循环引用，因为在block执行完，会释放掉bSelf。