解决NSTimer强引用问题

前言

NSTimer是我们日常开发用的比较多的，但是由于我们在设置target的时候通常都是传的self；系统在target内部会强引用当前的self，而一旦我们的NSTimer设置为成员变量或者属性的时候，那么timer就是当前self所持有，所以就导致了互相引用。

解决方案

1、在viewWillDisappear里面销毁timer（不推荐）
2、在didMoveToParentViewController内部释放
3、引入中间类，并动态添加方法
4、二次包装NSTimer
5、使用NSTimer的block方法（iOS10之后才能使用）
6、创建一个分类使用block回调
7、用NSProxy抽象类 (推荐使用)

一、在viewWillDisappear里面销毁timer

• 在viewWillAppear中创建timer
• 在viewWillDisappear中销毁timer

二、在didMoveToParentViewController内部释放

@property (nonatomic, strong) NSTimer *timer;

self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(__run) userInfo:nil repeats:YES];

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

三、引入中间类，并动态添加方法

导入头文件#import

    NSObject *obj = [[NSObject alloc] init];
    Method method = class_getInstanceMethod(object_getClass(self), @selector(__run));

    class_addMethod([obj class], @selector(__run), method_getImplementation(method), "v@:");
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:obj selector:@selector(__run) userInfo:nil repeats:YES];
    

四、二次包装NSTimer

LGSafeTimer 代码实现

@interface LGSafeTimer : NSObject

+ (LGSafeTimer *)lg_scheduledTimerWithTimeInterval:(NSTimeInterval)timerinterval
                                 target:(id)aTarget
                               selector:(SEL)aSelector
                               userInfo:(id)userInfo
                                repeats:(BOOL)repeats;
- (void)lg_inValidate;


@end

#import "LGSafeTimer.h"

@interface LGSafeTimer ()

@property (nonatomic, weak) id target;
@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, assign) SEL selector;



@end

@implementation LGSafeTimer


+ (LGSafeTimer *)lg_scheduledTimerWithTimeInterval:(NSTimeInterval)timerinterval
                                           target:(id)aTarget
                                         selector:(SEL)aSelector
                                         userInfo:(id)userInfo
                                          repeats:(BOOL)repeats {
    LGSafeTimer *timer = [[LGSafeTimer alloc] scheduledTimerWithTimeInterval:timerinterval
                                                                      target:aTarget
                                                                    selector:aSelector
                                                                    userInfo:userInfo
                                                                     repeats:repeats];
    return timer;
}

- (instancetype)scheduledTimerWithTimeInterval:(NSTimeInterval)timerinterval
                                        target:(id)aTarget
                                      selector:(SEL)aSelector
                                      userInfo:(id)userInfo
                                       repeats:(BOOL)repeats {
    if (self == [super init]) {
        self.target = aTarget;
        self.selector = aSelector;
        self.timer = [NSTimer scheduledTimerWithTimeInterval:timerinterval
                                                      target:self
                                                    selector:@selector(lg_safeTimerRun)
                                                    userInfo:userInfo
                                                     repeats:repeats];
        
    }
    return self;
}

- (void)lg_inValidate {
    [self.timer invalidate];
    self.timer = nil;
}
- (void)dealloc {
    NSLog(@"%@ --- %s", self, __func__);
}

#pragma mark - Private Methods

- (void)lg_safeTimerRun {
   
    
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    if ([self.target respondsToSelector:self.selector]) {
        [self.target performSelector:self.selector];
    }
#pragma clang diagnostic pop

}
@end

使用：

在dealloc函数内部需要释放timer

@property (nonatomic, strong) LGSafeTimer *safeTimer;
    self.safeTimer = [LGSafeTimer lg_scheduledTimerWithTimeInterval:1 target:self selector:@selector(__run) userInfo:nil repeats:YES];
    
 - (void)dealloc {
    NSLog(@"--------%s------dealloc", __func__);
    [self.safeTimer lg_inValidate];
}

五、创建一个分类使用block回调

NSTimer+LGSafeTimer实现

• 将定时器所执行的任务封装成Block，在调用定时器函数时，把block作为userInfo参数传进去
• 计时器现在的target是NSTimer类对象，这是个单例，因此计时器是否会保留它，其实都无所谓。此处依然有保留环，然而因为类对象（class object）无需回收，所以不用担心

+ (NSTimer *)lg_scheduledTimerWithTimeInterval:(NSTimeInterval)timerinterval
                                       repeats:(BOOL)repeats
                                         block:(void (^)(void))block {
    return [NSTimer scheduledTimerWithTimeInterval:timerinterval
                                            target:self
                                          selector:@selector(__fun:)
                                          userInfo:[block copy]
                                           repeats:repeats];
    
}

+ (void)__fun:(NSTimer *)timer {
    void(^block)(void) = timer.userInfo;
    if (block) {
        block();
    }
}

使用：

block内部注意循环引用

  self.timer = [NSTimer lg_scheduledTimerWithTimeInterval:1 repeats:YES block:^{
        NSLog(@"---------");
    }];

六、使用NSTimer的内部API

• 10.0以后才能使用**
• block内部注意循环引用**

  self.timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
        NSLog(@"---------");
    }];

七、NSProxy抽象类

LGProxy代码实现

@interface LGProxy : NSProxy
+ (instancetype)proxyWithObject:(id)object;

@end

#import "LGProxy.h"

@interface LGProxy ()

@property (nonatomic, weak) id object;

@end

@implementation LGProxy


+ (instancetype)proxyWithObject:(id)object {
    
    LGProxy *proxy = [LGProxy alloc];
    proxy.object = object;
    return proxy;
    
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    if (self.object) {
        return [self.object methodSignatureForSelector:sel];
    }
    return nil;
}
- (void)forwardInvocation:(NSInvocation *)invocation {
    if ([self.object respondsToSelector:invocation.selector]) {
        [invocation invokeWithTarget:self.object];
    }
}
@end

使用：

    LGProxy *proxy = [LGProxy proxyWithObject:self];
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:proxy selector:@selector(__run) userInfo:nil repeats:YES];