block循环引用解决

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。