iOS使用GCD实现一个Timer

由于 NSTimer 要加到 runloop 中才能工作,这样的话 runloop 在跑圈的时候,如果遇到了当前线程任务比较繁忙,那么它处理 NSTimer 的时机就会滞后,导致 NSTimer 不够准时.因为我们可以用 GCD 的 dispatch_soure_t 去实现一个自己的定时器,而且还比较准时不受 Runloop 影响

YVTimer API 设计 尽可能的仿照 NSTimer

@interface YVTimer : NSObject


/**
 定时器类方法创建 立即开启
 */
+ (instancetype)timerWithTimeInterval:(NSTimeInterval)ti
                            target:(id)aTarget
                          selector:(SEL)aSelector
                           repeats:(BOOL)yesOrNo;

/**
 定时器类方法创建 指定开启时间
 */
+ (instancetype)timerWithFireTime:(NSTimeInterval)start
                         interval:(NSTimeInterval)ti
                           target:(id)aTarget
                         selector:(SEL)aSelector
                          repeats:(BOOL)yesOrNo;


- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new UNAVAILABLE_ATTRIBUTE;

- (void) fire;
- (void) invalidate;

@property (readonly) BOOL repeats;
@property (readonly) NSTimeInterval timeInterval;
@property (readonly, getter=isValid) BOOL valid;

@end

实现代码也非常简单 就是对 GCD dispatch_source_t 的封装

#import "YVTimer.h"

#define LOCK  [_lock lock]
#define UNLOCK [_lock unlock]

@interface YVTimer ()
{
    id _target;
    NSTimeInterval _timeInterval;
    BOOL _repeats;
    dispatch_source_t _timer;
    SEL _selector;
    BOOL _valid;
    NSLock *_lock;
}
@end

@implementation YVTimer

+ (instancetype)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector repeats:(BOOL)yesOrNo {
    return [YVTimer timerWithFireTime:0.0f interval:ti target:aTarget selector:aSelector repeats:yesOrNo];
}

+ (instancetype)timerWithFireTime:(NSTimeInterval)start interval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector repeats:(BOOL)yesOrNo {
    return [[YVTimer alloc] initWithFireTime:start interval:ti target:aTarget selector:aSelector repeats:yesOrNo];
}


- (instancetype)initWithFireTime:(NSTimeInterval)start
                        interval:(NSTimeInterval)interval
                          target:(id)target
                        selector:(SEL)selector
                         repeats:(BOOL)repeats {
    
    if (self = [super init]) {
        _target = target;
        _selector = selector;
        _repeats = repeats;
        _timeInterval = interval;
        _valid = YES;
        _lock = [[NSLock alloc] init];
        
        __weak typeof(self)weakSelf = self;
        dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,dispatch_get_main_queue());
        dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, (start * NSEC_PER_SEC)), (interval * NSEC_PER_SEC), 0);
        dispatch_source_set_event_handler(timer, ^{
            [weakSelf fire];
        });
        dispatch_resume(timer);
        _timer = timer;
    }

    return self;
}

- (void) fire {
    if (!_valid) return;
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
    LOCK;
    id target = _target;
    if (!_target) {
        [self invalidate];
    } else {
        [target performSelector:_selector withObject:self];
        if (!_repeats) {
            [self invalidate];
        }
    }
    UNLOCK;
#pragma clang diagnostic pop
}

- (void)invalidate {
    LOCK;
    if (_valid) {
        dispatch_source_cancel(_timer);
        _timer = NULL;
        _target = nil;
        _valid = NO;
    }
    UNLOCK;
}

- (NSTimeInterval)timeInterval {
    LOCK;
    NSTimeInterval t = _timeInterval;
    UNLOCK;
    return t;
}

- (BOOL)repeats {
    LOCK;
    BOOL r = _repeats;
    UNLOCK;
    return r;
}

- (BOOL)isValid {
    LOCK;
    BOOL valid = _valid;
    UNLOCK;
    return valid;
}

- (void)dealloc
{
    [self invalidate];
    NSLog(@"timer dealloc");
}

@end

如何使用 建议设置 timer target 时候 不要直接使用当前类 self ,可以通过代理方式 用其他类的对象 去替代 self, 这个代理对象 内部可以弱引用 self ,并通过消息转发 去相应 self要执行的方法

image.png

@interface YVProxy : NSProxy

NS_ASSUME_NONNULL_BEGIN

+ (instancetype) proxyWithTarget:(id)target;
- (instancetype)initWithTarget:(id)target;
@property (nonatomic, weak, readonly) id target;

NS_ASSUME_NONNULL_END

@end


#import "YVProxy.h"

@interface YVProxy ()

@end

@implementation YVProxy


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

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

///消息转发 返回方法签名
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    return [self.target methodSignatureForSelector:sel];
}

/**
 消息转发 将方法交给其他对象去调用
 */
- (void)forwardInvocation:(NSInvocation *)invocation {
    [invocation invokeWithTarget:self.target];
}

- (void)dealloc
{
    NSLog(@"YVProxy dealloc");
}
@end

好了，我是大兵布莱恩特，欢迎加入博主技术交流群，iOS 开发交流群

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