iOS 定时器NSTimer自动释放

NSTimer是我们平时在项目中使用比较多的，但是使用的时候需要比较注意，需要在目标对象释放之前就要结束定时器，不然会造成内存泄露。
具体原因就是NSTimer的常用的方法：

+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;

这两个方法需要设置target，但是系统内部会对target强引用，导致target无法释放。
有的时候我们希望定时器在目标对象释放的时候能够自己结束，但是我们又无法直接修改系统内部的api。
这个时候我们可以利用利用一种比较简单地思路来实现：引入一个中间对象TimerDelegate，

image.png

将定时器的目标对象设为TimerDelegate，再由TimerDelegate去调用原target的方法，这样每次调用之前我们都可以知道target是否已经被释放了。

实现：

新建对象TimerDelegate

//  TimerDelegate.h

#import <Foundation/Foundation.h>

@interface TimerDelegate : NSObject

- (void)handleTarget:(id)aTarget  selector:(SEL)aSel  userInfo:(id)userInfo;


@property (weak,nonatomic)id desTarget;   //注意弱引用
@property (assign,nonatomic)SEL selector;
@property (strong,nonatomic)id userInfo;

用runtime交换这两个方法

//  NSTimer+Release.m
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        NSArray *selNameArray = @[@"scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:",@"timerWithTimeInterval:target:selector:userInfo:repeats:"];
        for (NSString *name in selNameArray) {
            SEL oriSel = NSSelectorFromString(name);
            NSString *newSelString = [NSString stringWithFormat:@"YT_%@",NSStringFromSelector(oriSel)];
            SEL newSel = NSSelectorFromString(newSelString);
            Class class = object_getClass((id)self);
            [RuntimeManager swizzleClass:class OrigionMethod:oriSel withNewMethod:newSel];
        }
    });
}

如果定时器不重复则不需要处理

+ (NSTimer *)YT_scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo{
    if(yesOrNo) {
    TimerDelegate *timerDelegate = [[TimerDelegate alloc]init];
    //将原目标对象和参数传递给delegate
    [timerDelegate handleTarget:aTarget selector:aSelector userInfo:userInfo];
    SEL sel = NSSelectorFromString(@"fireTimer:");
    
    //调用初始的方法,此处将定时器对象设置TimerDelegate, 然后调用TimerDelegate对象的fireTimer方法
    NSTimer* timer = [NSTimer YT_scheduledTimerWithTimeInterval:ti target:timerDelegate selector:sel userInfo:userInfo repeats:yesOrNo];
    return timer;
 
   }
    else {
    return  [self YT_scheduledTimerWithTimeInterval:ti target:aTarget selector:aSelector userInfo:userInfo repeats:yesOrNo];
    }
}

然后实现NStimerDelegate.m文件里的方法:

// NSTimerDelegate.m

- (void) fireTimer:(NSTimer *)timer {
    if(!_desTarget) {   //判断原对象是否已经释放
        [timer invalidate];
        timer = nil;
        return ;
    }
    //执行原目标对象的方法
  if ([_desTarget respondsToSelector:self.selector]) {
        #pragma clang diagnostic push
        #pragma clang diagnostic ignored "-Warc-performSelector-leaks"
       
        [self.desTarget performSelector:self.selector withObject:timer];

        #pragma clang diagnostic pop
    }
}