文章以在TimerViewController中使用计时器为例,在VC中声明一个NSTimer属性。
创建NSTimer对象:
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(startTimer) userInfo:nil repeats:YES];
timer作为VC的属性,被VC强引用,创建timer对象时VC作为target被timer强引用,即循环引用。
循环引用
解决循环引用的几种方式:
weak指针:
既然是强引用导致循环引用,那么用__weak修饰self就好了,想法是对的,但是做法是无效的。因为无论是weak还是strong修饰,在NSTimer中都会重新生成一个新的强引用指针指向self,导致循环引用的。
类方法:
创建一个继承NSObject的子类TempTarget,并创建开启计时器的方法。
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@property (nonatomic, assign) SEL selector; @property (nonatomic, weak) NSTimer *tempTimer; @property (nonatomic, weak) id tempTarget; + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)interval target:(id)tempTarget selector:(SEL)selector userInfo:(id)userInfo repeats:(BOOL)repeats;
TempTarget .m文件
@implementation TempTarget + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)interval target:(id)tempTarget selector:(SEL)selector userInfo:(id)userInfo repeats:(BOOL)repeats { TempTarget *target = [[TempTarget alloc] init]; target.tempTarget = tempTarget; target.selector = selector; target.tempTimer = [NSTimer scheduledTimerWithTimeInterval:interval target:target selector:@selector(timerSelector:) userInfo:userInfo repeats:repeats]; return target.tempTimer; } - (void)timerSelector:(NSTimer *)tempTimer { if (self.tempTarget && [self.tempTarget respondsToSelector:self.selector]) { [self.tempTarget performSelector:self.selector withObject:tempTimer.userInfo]; }else { [self.tempTimer invalidate]; } } @end
VC调用
self.timer = [TempTarget scheduledTimerWithTimeInterval:1 target:self selector:@selector(timerStart:) userInfo:nil repeats:YES];
VC强引用timer,因为timer的target是TempTarget实例,所以timer强引用TempTarget实例,而TempTarget实例弱引用VC,解除循环引用。
强引用转移
WeakProxy:
创建一个继承NSProxy的子类WeakProxy,并实现消息转发的相关方法。
WeakProxy.h文件
@property (nonatomic, weak, readonly) id weakTarget; + (instancetype)proxyWithTarget:(id)target; - (instancetype)initWithTarget:(id)target;
WeakProxy.m文件
@implementation WeakProxy + (instancetype)proxyWithTarget:(id)target { return [[self alloc] initWithTarget:target]; } - (instancetype)initWithTarget:(id)target { _weakTarget = target; return self; } - (void)forwardInvocation:(NSInvocation *)invocation { SEL sel = [invocation selector]; if ([self.weakTarget respondsToSelector:sel]) { [invocation invokeWithTarget:self.weakTarget]; } } //返回方法的签名。 - (NSMethodSignature *)methodSignatureForSelector:(SEL)sel { return [self.weakTarget methodSignatureForSelector:sel]; } - (BOOL)respondsToSelector:(SEL)aSelector { return [self.weakTarget respondsToSelector:aSelector]; } @end
VC调用
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:[WeakProxy proxyWithTarget:self] selector:@selector(timerStart:) userInfo:nil repeats:YES]; - (void)dealloc { [_timer invalidate]; NSLog(@"VC销毁了"); }
原理跟类方法相似,打破循环引用的环路。将timer的target设置为WeakProxy实例,利用消息转发机制实现执行VC中的计时方法,解决循环引用。
GCD:
VC的.m文件
@interface ViewController () @property (nonatomic, strong) dispatch_source_t timer; @end - (void)viewDidLoad { [super viewDidLoad]; dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0); self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue); dispatch_source_set_timer(_timer, dispatch_time(DISPATCH_TIME_NOW, 0), 0.1*NSEC_PER_SEC, 0); dispatch_source_set_event_handler(_timer, ^{ dispatch_async(dispatch_get_main_queue(), ^{ NSLog(@"执行了"); }); }); //开启计时器 dispatch_resume(_timer); }
//结束计时
dispatch_source_cancel(_timer);Block:
创建NSTimer的分类NSTimer+UnretainCycle。
+ (NSTimer *)lhScheduledTimerWithTimeInterval:(NSTimeInterval)inerval repeats:(BOOL)repeats block:(void(^)(NSTimer *timer))block { return [NSTimer scheduledTimerWithTimeInterval:inerval target:self selector:@selector(blcokInvoke:) userInfo:[block copy] repeats:repeats]; } + (void)blcokInvoke:(NSTimer *)timer { void (^block)(NSTimer *timer) = timer.userInfo; if (block) { block(timer); } }
VC调用
self.timer = [NSTimer mxScheduledTimerWithTimeInterval:0.5 repeats:YES block:^(NSTimer *timer) { NSLog(@"执行了"); }];
作者:皓皓大帝
链接:https://www.jianshu.com/p/aaf7b13864d9
来源:简书
著作权归作者所有。商业转载请联系作者获得授权,非商业转载请注明出处。
NSTimer循环引用解决方案
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转载自blog.csdn.net/li198847/article/details/104063375
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