iOS使用GCD實現一個Timer

由於 NSTimer 要加到 runloop 中才能工作,這樣的話 runloop 在跑圈的時候,如果遇到了當前執行緒任務比較繁忙,那麼它處理 NSTimer 的時機就會滯後,導致 NSTimer 不夠準時.因為我們可以用 GCD 的 dispatch_soure_t 去實現一個自己的定時器,而且還比較準時不受 Runloop 影響

YVTimer API 設計 儘可能的仿照 NSTimer

@interface YVTimer : NSObject


/**
 定時器類方法建立 立即開啟
 */
+ (instancetype)timerWithTimeInterval:(NSTimeInterval)ti
							target:(id)aTarget
						  selector:(SEL)aSelector
						   repeats:(BOOL)yesOrNo;

/**
 定時器類方法建立 指定開啟時間
 */
+ (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

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實現程式碼也非常簡單 就是對 GCD dispatch_source_t 的封裝

#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

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如何使用 建議設定 timer target 時候 不要直接使用當前類 self ,可以通過代理方式 用其他類的物件 去替代 self, 這個代理物件 內部可以弱引用 self ,並通過訊息轉發 去相應 self要執行的方法

@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;
}

///訊息轉發 返回方法簽名
- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
	return [self.target methodSignatureForSelector:sel];
}

/**
 訊息轉發 將方法交給其他物件去呼叫
 */
- (void)forwardInvocation:(NSInvocation *)invocation {
	[invocation invokeWithTarget:self.target];
}

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


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好了，我是大兵布萊恩特，歡迎加入博主技術交流群，iOS 開發交流群