循环引用的问题
让我们先来看一段代码。
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| @interface MyClass ()
@property (readonly) int val;
@property (strong) dispatch_block_t work;
@end
|
Capturing self strongly in this block is likely to lead to a retain cycle
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| @interface BlockTestView2 ()
@property (readonly) int val;
@property (nonatomic, strong) id obj;
@property (strong) dispatch_block_t work;
@end
@implementation BlockTestView2
- (instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
_obj = @1;
[self setup];
}
return self;
}
- (void)setup {
_val = 5;
// retain cycle
self.work = ^{
NSLog(@"BlockTestView2 %d", _val);
};
}
// 1. Scoping
// Avoid capturing self
- (void)setup1 {
int local = self.val;
self.work = ^{
NSLog(@"BlockTestView2 %d", local);
};
}
// 2. Programmatically
// nil the block property
- (void)setup2 {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-retain-cycles"
self.work = ^{
NSLog(@"BlockTestView2 %d", _val);
};
#pragma clang diagnostic pop
// nil the block property somewhere, please ignore
// this call at this point
[self cancel];
}
- (void)cancel {
self.work = nil;
}
// 3. Attributes
// Use __weak
- (void)setup3 {
__weak __typeof(self) weakSelf = self;
self.work = ^{
__strong __typeof(self) strongSelf = weakSelf;
NSLog(@"BlockTestView2 %@", strongSelf.obj);
};
}
@end
|
