NSTimer的使用

NSTimer的使用注意
一：循环引用问题
二：runloop的mode问题
三：在子线程中使用时需要启动runloop

使用方式一

#pragma mark - life cycle
- (void)dealloc
{
    if (_myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    NSLog(@"DMFunctionNSTimerOneViewController 释放");
}

#pragma mark - private method
- (void)startTime
{
    if (self.myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    self.totalTime = 60;
    
    // 方式一
    self.myTimer = [NSTimer timerWithTimeInterval:1 target:[DMWeakProxy proxyWithTarget:self] selector:@selector(myTimerAction) userInfo:nil repeats:YES];
    // 需要将NSTimer以指定的mode加入到runloop中
    [[NSRunLoop mainRunLoop] addTimer:self.myTimer forMode:NSRunLoopCommonModes];
}

- (void)myTimerAction
{
    if (self.totalTime >= 0) {
        NSLog(@"____%@", [NSNumber numberWithInteger:self.totalTime]);
        self.timeShowLabel.text = [NSString stringWithFormat:@"%@s", [NSNumber numberWithInteger:self.totalTime]];
        self.totalTime--;
    }
}

注意：
NSTimer使用重复调用时会强引用target,为了避免循环引用加入了DMWeakProxy类
当使用timerWithTimeInterval这种方式创建NSTimer时，需要将NSTimer加入到runloop中
DMWeakProxy.h

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface DMWeakProxy : NSProxy

@property (nonatomic, weak, readonly) id target;

- (instancetype)initWithTarget:(id)target;

+ (instancetype)proxyWithTarget:(id)target;

@end

NS_ASSUME_NONNULL_END

DMWeakProxy.m

#import "DMWeakProxy.h"

@implementation DMWeakProxy

- (instancetype)initWithTarget:(id)target
{
    _target = target;
    return self;
}

+ (instancetype)proxyWithTarget:(id)target
{
    return [[DMWeakProxy alloc] initWithTarget:target];
}

- (id)forwardingTargetForSelector:(SEL)selector
{
    return _target;
}

- (void)forwardInvocation:(NSInvocation *)invocation
{
    void *null = NULL;
    [invocation setReturnValue:&null];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector
{
    return [NSObject instanceMethodSignatureForSelector:@selector(init)];
}

- (BOOL)respondsToSelector:(SEL)aSelector
{
    return [_target respondsToSelector:aSelector];
}

- (BOOL)isEqual:(id)object
{
    return [_target isEqual:object];
}

- (NSUInteger)hash
{
    return [_target hash];
}

- (Class)superclass
{
    return [_target superclass];
}

- (Class)class
{
    return [_target class];
}

- (BOOL)isKindOfClass:(Class)aClass
{
    return [_target isKindOfClass:aClass];
}

- (BOOL)isMemberOfClass:(Class)aClass
{
    return [_target isMemberOfClass:aClass];
}

- (BOOL)conformsToProtocol:(Protocol *)aProtocol
{
    return [_target conformsToProtocol:aProtocol];
}

- (BOOL)isProxy
{
    return YES;
}

- (NSString *)description
{
    return [_target description];
}

- (NSString *)debugDescription
{
    return [_target debugDescription];
}

@end

1

可以看到DMFunctionNSTimerOneViewController正常释放
方式二

#pragma mark - life cycle
- (void)dealloc
{
    if (_myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    NSLog(@"DMFunctionNSTimerTwoViewController 释放");
}

#pragma mark - private method
- (void)startTime
{
    if (self.myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    self.totalTime = 60;
    
    // 方式二
    // 这种方式启动的timer默认加到runloop的defalultModel中，会导致UIScrollView滑动过程中定时器失效
    self.myTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:[DMWeakProxy proxyWithTarget:self] selector:@selector(myTimerAction) userInfo:nil repeats:YES];
 
}

- (void)myTimerAction
{
    if (self.totalTime >= 0) {
        NSLog(@"____%@", [NSNumber numberWithInteger:self.totalTime]);
        self.timeShowLabel.text = [NSString stringWithFormat:@"%@s", [NSNumber numberWithInteger:self.totalTime]];
        self.totalTime--;
    }
}

注意
NSTimer 使用scheduledTimerWithTimeInterval方式时会默认加入到runloop的defalultModel中,会导致UIScrollView滑动过程中定时器失效

2

可以看到DMFunctionNSTimerTwoViewController正常释放
方式三：在子线程中使用NSTimer

#pragma mark - life cycle
- (void)dealloc
{
    if (_myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    if (_myThread) {
        [self stop];
    }
    NSLog(@"DMFunctionNSTimerThreeViewController 释放");
}
#pragma mark - private method
- (void)startTime
{
    if (self.myTimer) {
        [self.myTimer invalidate];
        self.myTimer = nil;
    }
    
    self.myTimer = [NSTimer timerWithTimeInterval:1 target:[DMWeakProxy proxyWithTarget:self] selector:@selector(threadTimerRun) userInfo:nil repeats:YES];
    
    __weak typeof(self) weakSelf = self;
    self.myThread = [[DMThread alloc] initWithBlock:^{
        [[NSRunLoop currentRunLoop] addTimer:weakSelf.myTimer forMode:NSRunLoopCommonModes];
        // 这里需要注意不要使用[[NSRunLoop currentRunLoop] run]
        // 因为通过run方法开启的runloop是无法停止的
        while (weakSelf && !weakSelf.stopTimer) {
            [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
        }
    }];
    [self.myThread start];
}

- (void)threadTimerRun
{
    NSLog(@"thread - %@ - %s", [NSThread currentThread], __func__);
}

- (void)stop
{
    [self performSelector:@selector(stopThread) onThread:self.myThread withObject:nil waitUntilDone:YES];
}

// 用于停止子线程的RunLoop
- (void)stopThread
{
    // 设置标记为YES
    self.stopTimer = YES;
    // 停止RunLoop
    CFRunLoopStop(CFRunLoopGetCurrent());
    // 清空线程
    self.myThread = nil;
}

注意
在子线程中使用NSTimer时，需要注意子线程默认没有开启runloop，需要手动开启runloop
DMThread.h

NS_ASSUME_NONNULL_BEGIN

@interface DMThread : NSThread

@end

NS_ASSUME_NONNULL_END

DMThread.m

#import "DMThread.h"

@implementation DMThread

- (void)dealloc
{
    NSLog(@"DMThread 释放");
}

+ (void)exit
{
    NSLog(@"DMThread exit");
    [super exit];
}

@end

3

可以看到DMFunctionNSTimerThreeViewController以及DMThread线程正常释放