NSTimer使用时处理不好容易造成循环引用，导致控制器无法正常释放。之前使用的方法或多或少都会在某些特定环境下造成一些问题。今天正好学习到了3种解决循环引用的方法，在这里记录一下。

1.在didMoveToParentViewController:中取消NSTimer强引用

- (void)didMoveToParentViewController:(UIViewController *)parent{
    if (!parent) {
        [self.timer invalidate];
        self.timer = nil;
    }
}

2.利用target属性和class_addMethod，使NSTimer不直接强引用self

@property (nonatomic , strong) id target;

_target = [NSObject new];
class_addMethod([_target class], @selector(update), (IMP)update, "v@:");
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:_target selector:@selector(update) userInfo:nil repeats:YES];

void update(id self,SEL _cmd)
{
    NSLog(@"class_addMethod ----> update");
}

- (void)dealloc
{
    [self.timer invalidate];
    self.timer = nil;
}

3.利用NSProxy类(推荐)
在YYText中就使用到了YYTextWeakProxy作为代理中间类。有兴趣的可以去看看

//DEProxy.h
@interface DEProxy : NSProxy
@property (nonatomic , weak) id target;
@end


//DEProxy.m
@implementation DEProxy
//1.1.标准转发-签名
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel
{
    return [_target methodSignatureForSelector:sel];
}
//1.2.标准转发-转发
- (void)forwardInvocation:(NSInvocation *)invocation{
    [invocation invokeWithTarget:_target];
}
//2.快速转发
//- (id)forwardingTargetForSelector:(SEL)selector {
//    return _target;
//}
@end

//使用
@property (nonatomic , strong) DEProxy *targetProxy;

_targetProxy = [DEProxy alloc];
_targetProxy.target = self;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:_targetProxy selector:@selector(update) userInfo:nil repeats:YES];

-(void)update{
    NSLog(@"update");
}

- (void)dealloc
{
    [self.timer invalidate];
    self.timer = nil;
}

4.在iOS10以后，NSTimer新增了block方法来解决循环引用问题

    if (@available(iOS 10.0, *)) {
        self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
            NSLog(@"update");
        }];
    } else {
        // Fallback on earlier versions
    }

- (void)dealloc
{
    [self.timer invalidate];
    self.timer = nil;
}