因为一个NStimer的循环引用没有释放问题，导致一次性会走两遍的回调
问题所在
self.timer = [NSTimer scheduledTimerWithTimeInterval:5.0
target:self
selector:@selector(doTimeEvent)
userInfo:nil repeats:YES];
置于循环引用的原因，vc强引用timer，timer又强引用他的target，而target又是self，self也就是vc了。这就形成了一个环。
image.png
解决
如何解决呢？无非就是打破这个环。
首先苹果的api已经解决了这个问题，但是只支持10.0的api。
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)interval repeats:(BOOL)repeats block:(void (^)(NSTimer *timer))block API_AVAILABLE(macosx(10.12), ios(10.0), watchos(3.0), tvos(10.0));
下面就来看看，各路大神是如何解决的这个问题。
首先是YYKIt的解决办法，一直在用，各种block，用的不亦乐乎
@interface NSTimer (YYAdd)
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds block:(void (^)(NSTimer *timer))block repeats:(BOOL)repeats;
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)seconds block:(void (^)(NSTimer *timer))block repeats:(BOOL)repeats;
@end
YYSYNTH_DUMMY_CLASS(NSTimer_YYAdd)
@implementation NSTimer (YYAdd)
+ (void)_yy_ExecBlock:(NSTimer *)timer {
if ([timer userInfo]) {
void (^block)(NSTimer *timer) = (void (^)(NSTimer *timer))[timer userInfo];
block(timer);
}
}
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds block:(void (^)(NSTimer *timer))block repeats:(BOOL)repeats {
return [NSTimer scheduledTimerWithTimeInterval:seconds target:self selector:@selector(_yy_ExecBlock:) userInfo:[block copy] repeats:repeats];
}
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)seconds block:(void (^)(NSTimer *timer))block repeats:(BOOL)repeats {
return [NSTimer timerWithTimeInterval:seconds target:self selector:@selector(_yy_ExecBlock:) userInfo:[block copy] repeats:repeats];
}
@end
从代码中我们可以很清楚的看到，yykit是把nstimer自身作为target，来调用自己的方法，
然后通过userinfo把block传过去，从而实现以一种相当优雅的形式来解决weaktimer的问题。
下面说的这两种方法都是从同一个人的博客中看到的。
其实也是提供了另外两种思路。
利用RunTime解决由NSTimer导致的内存泄漏
利用NSProxy解决NSTimer内存泄漏问题
首先是利用runtime解决
来看具体代码实现
@interface TableViewController ()
@property (nonatomic,strong) id timerTarget;
@end
static const void * TimerKey = @"TimerKey";
static const void * weakKey = @"weakKey";
@implementation TableViewController
- (void)viewDidLoad {
[super viewDidLoad];
_timerTarget = [NSObject new];
//初始化timerTarge对象
class_addMethod([_timerTarget class], @selector(timerEvent), (IMP)timMethod, "v@:");
//动态创建timerEvent方法
NSTimer *_timer;
_timer = [NSTimer timerWithTimeInterval:1 target:_timerTarget selector:@selector(timerEvent) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:_timer forMode:NSRunLoopCommonModes];
//创建计时器target对象为_timerTarget
objc_setAssociatedObject(_timerTarget, TimerKey, _timer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
objc_setAssociatedObject(_timerTarget, weakKey, self, OBJC_ASSOCIATION_ASSIGN);
//将self对象与NSTimer对象与_timerTarget对象关联
}
void timMethod(id self,SEL _cmd)
{
TableViewController *tabview = objc_getAssociatedObject(self, weakKey);
[tabview performSelector:_cmd];
}
-(void)timerEvent
{
NSLog(@"%@",NSStringFromClass([self class]));
}
-(void)dealloc
{
NSTimer *timer = objc_getAssociatedObject(_timerTarget, TimerKey);
[timer invalidate];
NSLog(@"%@--dealloc",NSStringFromClass([self class]));
}
首先添加了timMethod 的IMP 然后利用runtime为timeTarget类添加方法。
timeTarget就是nstimer的target。
OBJC_ASSOCIATION_RETAIN_NONATOMIC和OBJC_ASSOCIATION_ASSIGN分别代表强引用和弱引用。也就是说self. timerTarget是弱引用的。这样就不会引起释放不了的问题。
第二种是NSProxy来解决的，结合消息转发来解决的。
好早就知道NSProxy是根类，NSProxy与NSObject一样是根类，都遵守<NSObject>协议。
NSProxy与NSObject的子类都能实现，不过NSProxy从类名来看是代理类专门负责代理对象转发消息的。相比NSObject类来说NSProxy更轻量级，通过NSProxy可以帮助Objective-C间接的实现多重继承的功能。
说到消息转发无非就是那三个步骤。
+(BOOL)resolveClassMethod:(SEL)sel;
-(BOOL)respondsToSelector:(SEL)aSelector;
-(id)forwardingTargetForSelector:(SEL)aSelector;
-(NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector;
- (void)forwardInvocation:(NSInvocation *)invocation;
来看下作者是怎么实现的。
.h文件
#import <UIKit/UIKit.h>
@interface LSYViewController : UIViewController
@end
@interface LSYProxy : NSProxy
@property (nonatomic,weak) id obj;
@end
.m文件
#import "LSYViewController.h"
@interface LSYViewController ()
@property (nonatomic,strong) LSYProxy *proxy;
@property (nonatomic,strong) NSTimer *timer;
@property (nonatomic) NSInteger count;
@end
@implementation LSYViewController
-(void)viewDidLoad
{
[super viewDidLoad];
self.proxy = [LSYProxy alloc];
self.proxy.obj = self;
_timer = [NSTimer timerWithTimeInterval:1 target:self.proxy selector:@selector(timerEvent) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:_timer forMode:NSRunLoopCommonModes];
}
-(void)timerEvent
{
NSLog(@"count---%d",(int)++_count);
}
-(void)dealloc
{
NSLog(@"---dealloc----");
[_timer invalidate];
}
@end
#pragma mark - LSYProxy Implementation
@implementation LSYProxy
- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
NSMethodSignature *sig;
sig = [self.obj methodSignatureForSelector:aSelector];
return sig;
}
- (void)forwardInvocation:(NSInvocation *)invocation {
[invocation invokeWithTarget:self.obj];
}
@end
利用消息转发的第三步，来给方法重新签名，重新设置target。利用消息转发来断开NSTimer对象与视图之间的引用关系。其实看了上面的代码，应该都能明白作者是怎么个想法。
剩下的这种也是某位大神所写的插件 MSWeakTimer，也是相当牛逼，是根据GCD来搞的。
为什么要拿GCD来搞呢？因为NSTimer的启动和失效必须都是在同一个线程调用，否则可能没用。所以就要用GCD自带的计时器
@interface MSWeakTimer ()
{
struct
{
uint32_t timerIsInvalidated;
} _timerFlags;
}
@property (nonatomic, assign) NSTimeInterval timeInterval;
@property (nonatomic, weak) id target;
@property (nonatomic, assign) SEL selector;
@property (nonatomic, strong) id userInfo;
@property (nonatomic, assign) BOOL repeats;
@property (nonatomic, ms_gcd_property_qualifier) dispatch_queue_t privateSerialQueue;
@property (nonatomic, ms_gcd_property_qualifier) dispatch_source_t timer;
@end
+ (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)timeInterval
target:(id)target
selector:(SEL)selector
userInfo:(id)userInfo
repeats:(BOOL)repeats
dispatchQueue:(dispatch_queue_t)dispatchQueue
{
MSWeakTimer *timer = [[self alloc] initWithTimeInterval:timeInterval
target:target
selector:selector
userInfo:userInfo
repeats:repeats
dispatchQueue:dispatchQueue];
[timer schedule];
return timer;
}
- (id)initWithTimeInterval:(NSTimeInterval)timeInterval
target:(id)target
selector:(SEL)selector
userInfo:(id)userInfo
repeats:(BOOL)repeats
dispatchQueue:(dispatch_queue_t)dispatchQueue
{
NSParameterAssert(target);
NSParameterAssert(selector);
NSParameterAssert(dispatchQueue);
if ((self = [super init]))
{
//把nstimer所需要的所有参数都拿出来，除了userinfo都是弱引用修饰
self.timeInterval = timeInterval;
self.target = target;
self.selector = selector;
self.userInfo = userInfo;
self.repeats = repeats;
NSString *privateQueueName = [NSString stringWithFormat:@"com.mindsnacks.msweaktimer.%p", self];
self.privateSerialQueue = dispatch_queue_create([privateQueueName cStringUsingEncoding:NSASCIIStringEncoding], DISPATCH_QUEUE_SERIAL);//新建一个串行队列
dispatch_set_target_queue(self.privateSerialQueue, dispatchQueue);//保证目标队列再串行队列里执行
self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER,
0,
0,
self.privateSerialQueue);//GCD里面的时间计时器
}
return self;
}
#pragma mark -
- (void)setTolerance:(NSTimeInterval)tolerance //这里是等待时间的意思
{
@synchronized(self)//加锁保证安全
{
if (tolerance != _tolerance)
{
_tolerance = tolerance;
[self resetTimerProperties];
}
}
}
//通过查阅资料，对于tolerance有这样一个解释
由于系统底层的调度优化关系，当我们使用定时器调用fired的时候并不能立马就能运行的。可能马上运行，也可能需要等一段时间（如果当前CPU忙着做别的事情）。当时我们可以设置一个最大等待时间。
对于刚创建的timer第一次在start时间点fire，那么这个fire的时间上限为'leeway',即第一次fire不会晚于'start' + 'leeway' 。
对于重复了N次的fire，那么这个时间上限就是 MIN('leeway','interval'/2)。
如果我们使用了参数DISPATCH_TIMER_STRICT，那么系统将尽最大可能去"尽早
"启动定时器，即使DISPATCH_TIMER_STRICT比当前的发射延迟下限还低。注意就算这样，还是会有微量的延迟。
MSWeakTimer中对于这个参数就是重新包装一下，名字叫tolerance，更好理解一点。
- (NSTimeInterval)tolerance
{
@synchronized(self)
{
return _tolerance;
}
}
- (void)resetTimerProperties
{
int64_t intervalInNanoseconds = (int64_t)(self.timeInterval * NSEC_PER_SEC);
int64_t toleranceInNanoseconds = (int64_t)(self.tolerance * NSEC_PER_SEC);
dispatch_source_set_timer(self.timer,
dispatch_time(DISPATCH_TIME_NOW, intervalInNanoseconds),
(uint64_t)intervalInNanoseconds,
toleranceInNanoseconds//最大等待时间
);
}
- (void)schedule
{
[self resetTimerProperties];
__weak MSWeakTimer *weakSelf = self;
dispatch_source_set_event_handler(self.timer, ^{//执行倒计时
[weakSelf timerFired];
});
dispatch_resume(self.timer);
}
- (void)fire
{
[self timerFired];
}
- (void)invalidate
{
// We check with an atomic operation if it has already been invalidated. Ideally we would synchronize this on the private queue,
// but since we can't know the context from which this method will be called, dispatch_sync might cause a deadlock.
//在这里采用异步方法去取消计时器的原因是防止死锁
if (!OSAtomicTestAndSetBarrier(7, &_timerFlags.timerIsInvalidated))//这一块是我只知道是原子性相关的东西，应该是准确度更高，也看起来更高大上一点。
{
dispatch_source_t timer = self.timer;
dispatch_async(self.privateSerialQueue, ^{
dispatch_source_cancel(timer);
ms_release_gcd_object(timer);
});
}
}
- (void)timerFired
{
// Checking attomatically if the timer has already been invalidated.
if (OSAtomicAnd32OrigBarrier(1, &_timerFlags.timerIsInvalidated))
{
return;
}
// We're not worried about this warning because the selector we're calling doesn't return a +1 object.
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[self.target performSelector:self.selector withObject:self];
#pragma clang diagnostic pop
if (!self.repeats)
{
[self invalidate];
}
}
