iOS 解决NSTimer的循环引用问题

iOS 13以后可以通过block解决target的强引用问题，如果程序兼顾iOS13以下，那么使用NSProxy是最好的解决办法：

@interface timerProxy : NSProxy

//通过创建对象
- (instancetype)initWithObjc:(id)object;

//通过类方法创建创建
+ (instancetype)proxyWithObjc:(id)object;

@end

@interface timerProxy ()
@property (nonatomic, weak) id object;

@end

@implementation timerProxy

- (instancetype)initWithObjc:(id)object {
    
    self.object = object;
    return self;
}

+ (instancetype)proxyWithObjc:(id)object {
    
    return [[self alloc] initWithObjc:object];
}

- (void)forwardInvocation:(NSInvocation *)invocation {
    
    if ([self.object respondsToSelector:invocation.selector]) {
        
        [invocation invokeWithTarget:self.object];
    }
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    
    return [self.object methodSignatureForSelector:sel];
}

@end

使用的时候：

    timerProxy* proxy = [timerProxy proxyWithObjc:self];
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:proxy selector:@selector(timerAction) userInfo:nil repeats:YES];