在ARC中，dealloc方法调用包含对self的弱引用的method / block，从而导致weakSelf = nil

Question

As the title states, in ARC mode, when I define a block using self reference (weak to avoid reference cycle):

...
id __weak weakSelf = self;
self.someBlock = ^(){
    if (weakSelf != nil){
        (do something with weakSelf...)
        return NO;
    }
    return YES;
};
...

In dealloc I call the block:

- (void)dealloc {
    ...
    BOOL isNil = self.someBlock();
    ...
}

Then I found isNil = YES.

When I want blocks in dealloc to do something with self, this seems to be a problem.

This also happen in callback functions, which I will not give an example here.

My solution is using __unsafe_unretained instead of __weak.

But this looks ugly.

Is there better ways to avoid nil weak self in dealloc?

Updated Question: Why weakSelf is niled even when self is not? Is it the reason of dealloc ?

---

To make it clear, I paste the test code below:

#import <Foundation/Foundation.h>

@interface blockWeak : NSObject

@property (nonatomic, strong) BOOL (^someBlock)();
@property (nonatomic) int num;

- (void)makeBlock;

@end

@implementation blockWeak

- (void)makeBlock
{
    typeof(self) __weak weakSelf = self;
    self.someBlock = ^(){
        typeof(self) strongSelf = weakSelf;
        strongSelf.num = 2;
        return weakSelf == nil?YES:NO;
    };
}

- (void)dealloc
{
    BOOL isNil = self.someBlock();
    if (isNil) {
        NSLog(@"weakSelf is nil.");
    }
}

@end

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        blockWeak *bw = [[blockWeak alloc] init];
        bw.num = 1;
        [bw makeBlock];
    }
    return 0;
}

Answer 1

You do not call the block. That would be:

BOOL isNil = self.someBlock();

Answer 2

The below works, and in my opinion is cleaner as no reference to self is then held. Also there is no real need for the return BOOL of the block now, but I've left this in...

#import <Foundation/Foundation.h>

@interface blockWeak : NSObject

@property (nonatomic, copy) BOOL (^someBlock)(blockWeak *);
@property (nonatomic) int num;

- (void)makeBlock;

@end

@implementation blockWeak

- (void)makeBlock
{
    self.someBlock = ^BOOL(blockWeak *object){
        object.num = 2;
        return object == nil?YES:NO;
    };
}

- (void)dealloc
{
    NSLog(@"num = %d", _num);
    BOOL isNil = _someBlock(self);
    if (isNil) {
        NSLog(@"block returned NO");
    } else {
        NSLog(@"block returned YES");
    }
    NSLog(@"num = %d", _num);
}

@end

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        blockWeak *bw = [[blockWeak alloc] init];
        bw.num = 1;
        [bw makeBlock];
    }
    return 0;
}

Output :

num = 1
block returned YES
num = 2