1、计时器创建

1）第一种 默认直接开启

//NSTimer第一种写法
[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(runTimerMethed) userInfo:nil repeats:YES];

2）第二种

@property (nonatomic,strong)NSTimer *timer;

//NSTimer第二种写法
self.timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:@selector(runTimerMethed) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop]addTimer:self.timer forMode:NSRunLoopCommonModes];

- (void)runTimerMethed{
    NSLog(@"计时器走了--");
}

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

2、下面进行操作

当前页面为vc1，前一个页面为vc，后一个页面为vc2
1、从vc进入vc1，计时器方法开始执行，pop回vc，计时器还在跑，dealloc方法不会执行

原因：timer被runloop持有，timer释放不掉，timer又持有self，所以导致self释放不掉。不会走dealloc方法。

循环引用关系图

那就想办法～～～

- (void)viewWillDisappear:(BOOL)animated{
    [super viewWillDisappear:animated];
    [self.timer invalidate];
    self.timer = nil;
}

从vc1pop回vc，可以正常dealloc了
but
从vc1进入vc2，计时器停掉了，再返回vc1，计时器开始跑，不准，pass掉该方法

3、解决方案

1）第一种：

//添加、移除进navi里执行该方法  parent = UINavigationController
- (void)didMoveToParentViewController:(UIViewController *)parent{
    if (parent == nil) {
        [self.timer invalidate];
        self.timer = nil;
    }
}

2）第二种：中间对象

原理图：

target原理图

@property (nonatomic,strong)NSObject *target;

_target = [[NSObject alloc]init];
class_addMethod([_target class], @selector(runTimerMethed), (IMP)runMethedIMP, "v@:");
self.timer = [NSTimer timerWithTimeInterval:1.0f target:_target selector:@selector(runTimerMethed) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop]addTimer:self.timer forMode:NSRunLoopCommonModes];

void runMethedIMP(id self,SEL _cmd){
    NSLog(@"IMP计时器走了--");
}
- (void)dealloc{
    NSLog(@"dealloc");
    [self.timer invalidate];
    self.timer = nil;
}

3）第二种：NSProxy

橙色箭头：强引用
绿色箭头：弱引用

NSProxy原理图示

@interface HHProxy : NSProxy

@property (weak,nonatomic)id target;

@end

#import "HHProxy.h"

@implementation HHProxy

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel{
    return [_target methodSignatureForSelector:sel];
}

- (void)forwardInvocation:(NSInvocation *)invocation{
    [invocation invokeWithTarget:_target];
}
@end

调用：

_proxy = [HHProxy alloc];
_proxy.target = self;
self.timer = [NSTimer timerWithTimeInterval:1.0f target:_proxy selector:@selector(runTimerMethed) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop]addTimer:self.timer forMode:NSRunLoopCommonModes];