OC Block + RAC strongify/weakify原理

探究方法:利用clang把oc实现转成cpp实现:

xcrun -sdk iphonesimulator  clang -rewrite-objc -fobjc-arc -stdlib=libc++ -mmacosx-version-min=10.7 -fobjc-runtime=macosx-10.7 -Wno-deprecated-declarations -F /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk/System/Library/Frameworks  main.m
翻译前后源码对比:

翻以前:

OC Block + RAC strongify/weakify原理_第1张图片
DEAF2789-EB63-4502-AC8E-9BDCDDE9E7A0.png

翻以后:

OC Block + RAC strongify/weakify原理_第2张图片
B40EF58E-C1CE-493E-AD48-75D5C9ED79D5.png
问题1描述:

问:这样会循环引用吗?


@interface ViewController : UITableViewController

@property (nonatomic, copy) void (^myUniqueTestBlock)(void);

@property (nonatomic, copy) void (^myAnotherUniqueTestBlock)(void);

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    @weakify(self) 

    self.myUniqueTestBlock = ^(void){

        [self.view addSubview:[[UIView alloc] init]];

    };

}

@end

答:会,15行给block赋值的时候,会生成一个名为__ViewController__viewDidLoad_block_impl_0的struct作为对这个block的定义,其中一个成员即为:__strong typeof (self) self; 此时,用于初始化这个结构体的构造函数__ViewController__viewDidLoad_block_impl_0的参数也传的是self(不过这不是实质,实质还是定义中就是strong)。至于这个struct是怎么生成的,为什么是__strong typeof (self) self,待我再探究一下,就目前来看,用到谁了,结构体里就会出现同名同类型的变量。


@interface ViewController : UITableViewController

@property (nonatomic, copy) void (^myUniqueTestBlock)(void);

@property (nonatomic, copy) void (^myAnotherUniqueTestBlock)(void);

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    @weakify(self) // 翻译成:__attribute__((objc_ownership(weak))) __typeof__(self) self_weak_ = (self);

    self.myUniqueTestBlock = ^(void){  // 此处传给__ViewController__viewDidLoad_block_impl_0(block结构体构造函数)的的参数也为self

        [self.view addSubview:[[UIView alloc] init]];

    };

}

@end
问题2描述:

问:如下19行开始的block,内外还需要使用weakify strongify对吗?


@interface ViewController : UITableViewController

@property (nonatomic, copy) void (^myUniqueTestBlock)(void);

@property (nonatomic, copy) void (^myAnotherUniqueTestBlock)(void);

@end

@implementation ViewController

- (void)viewDidLoad {

    [super viewDidLoad];

    @weakify(self) 

    self.myUniqueTestBlock = ^(void){

  @strongify(self) 

        [self.view addSubview:[[UIView alloc] init]];

        self.myAnotherUniqueTestBlock = ^(void){ 

  [self.view addSubview:[[UIView alloc] init]];

        };

    };

}

@end

问题2回答:同上,要用,不然还是拿的self

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