CADispalyLink
计时器对象，与屏幕的刷新率同步。
iOS设备的屏幕刷新频率是固定的，其精度相当准确，一般用于做UI界面的不停重绘。
CADisplayLink *displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(run)];
//设置 CADisplayLink selector 调用时间间隔
displayLink.preferredFramesPerSecond = 1;
//添加到 runloop，并指定 RunloopMode
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
//暂停
[displayLink setPaused:YES];
//停止使用
[displayLink invalidate];
NSTimer
NSTimer的使用
NSTimer比较常用的创建方法有以下两种：
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;
scheduledTimerWithTimeInterval在主线程创建的定时器会在创建后自动将timer添加到主线程的RunLoop中并启动，主线程的RunLoopMode为NSDefaultRunLoopMode,如果有滚动视图并滑动的时候，执行的是UITrackingRunLoopMode,NSDefaultRunLoopMode被挂起，定时器失效，等到滑动结束才恢复。
因此需要将timer分别加入UITrackingRunLoopMode和NSDefaultRunLoopMode中：
[[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
[[NSRunLoop mainRunLoop] addTimer:self.timer forMode:UITrackingRunLoopMode];
或者直接添加到 NSRunLoopCommonModes中：
[[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
也可以新开一个子线程，主线程的RunLoop默认是开启的，子线程的RunLoop需要手动开启：
[NSThread detachNewThreadWithBlock:^{
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
NSLog(@"111");
}];
[[NSRunLoop currentRunLoop] run];
}];
//如果使用 timerWithTimeInterval创建，创建的定时器不会直接启动， 需要手动添加到RunLoop中
[NSThread detachNewThreadWithBlock:^{
self.timer = [NSTimer timerWithTimeInterval:1.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
NSLog(@"111");
}];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
[[NSRunLoop currentRunLoop] run];
}];
NSTimer循环引用的解决方法
创建中间类解决
创建个继承自NSObject的类
@interface LWTProxy : NSObject
+ (instancetype)proxyWithTarget:(id)target;
@property (nonatomic, weak)id target;
@end
#import "LWTProxy.h"
#import <objc/runtime.h>
@implementation LWTProxy
+ (instancetype)proxyWithTarget:(id)target {
LWTProxy *proxy = [[LWTProxy alloc] init];
proxy.target = target;
return proxy;
}
//消息转发
- (id)forwardingTargetForSelector:(SEL)aSelector {
return self.target;
}
@end
使用
//添加个中间对象，解决timer的循环引用问题
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:[LWTProxy proxyWithTarget:self] selector:@selector(run) userInfo:nil repeats:YES];
也可以使用NSProxy来解决循环引用。
创建一个继承自NSProxy的类，
使用 block 来解决
创建一个 NSTimer (Weak)
@interface NSTimer (Weak)
+ (NSTimer *)weak_scheduledTimerWithTimeInterval:(NSTimeInterval)interval block:(void(^)())block repeats:(BOOL)repeats;
+ (NSTimer *)weak_timerWithTimeInterval:(NSTimeInterval)interval repeats:(BOOL)repeats block:(void(^)())block;
@end
@implementation NSTimer (Weak)
+ (NSTimer *)weak_scheduledTimerWithTimeInterval:(NSTimeInterval)interval block:(void(^)())block repeats:(BOOL)repeats {
NSTimer *t = [self scheduledTimerWithTimeInterval:interval
target:self
selector:@selector(_invoke:)
userInfo:[block copy]
repeats:repeats];
return t;
}
+ (NSTimer *)weak_timerWithTimeInterval:(NSTimeInterval)interval repeats:(BOOL)repeats block:(void(^)())block {
NSTimer * t = [self timerWithTimeInterval:interval
target:self
selector:@selector(_invoke:)
userInfo:[block copy]
repeats:repeats];
return t;
}
+ (void)_invoke:(NSTimer *)timer {
void (^_block)() = timer.userInfo;
if (_block) {
_block();
}
}
@end
使用时需注意，先定义了一个弱引用，令其指向self，然后使块捕获这个引用，而不直接去捕获普通的self变量。也就是说，self不会为计时器所保留。当块开始执行时，立刻生成strong引用，以保证实例在执行期间持续存活。
__weak XXClass *weakSelf = self;
self.timer = [NSTimer weak_scheduledTimerWithTimeInterval:1.0 block:^{
XXClass *strongSelf = weakSelf;
[strongSelf doSomething];
} repeats:YES];
NSTimer为什么不准
情况产生：
1、NSTimer被添加在mainRunLoop中，模式是NSDefaultRunLoopMode，mainRunLoop负责所有主线程事件，例如UI界面的操作，复杂的运算使当前RunLoop持续的时间超过了定时器的间隔时间，那么下一次定时就被延后，这样就会造成timer的阻塞、2：模式的切换，当创建的timer被加入到NSDefaultRunLoopMode时，此时如果有滑动UIScrollView的操作，runLoop 的mode会切换为TrackingRunLoopMode，这时timer会停止回调。
GCD定时器
GCD 定时器比 NSTimer 更精确，定时器一定要被强引用，不然会被释放，导致的定时器无效。
创建一个GCD定时器LWTTimer
@interface LWTTimer : NSObject
//方法一
+ (NSString *)exeTask:(void(^)(void))task
start:(NSTimeInterval)start
interval:(NSTimeInterval)interval
repeats:(BOOL)repeats async:(BOOL)async;
//方法二
+ (NSString *)exeTask:(id)target
selector:(SEL)selector
start:(NSTimeInterval)start
interval:(NSTimeInterval)interval
repeats:(BOOL)repeats async:(BOOL)async;
+ (void)cancelTask:(NSString *)taskName;
@end
@implementation LWTTimer
static NSMutableDictionary *timers;
dispatch_semaphore_t semaphore_;
+ (void)initialize {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
timers = [NSMutableDictionary dictionary];
});
//因为可能会在多个线程都调用这个timer，全局字典不能同时存、取，所以要加锁
semaphore_ = dispatch_semaphore_create(1);
}
+ (NSString *)exeTask:(void(^)(void))task
start:(NSTimeInterval)start
interval:(NSTimeInterval)interval
repeats:(BOOL)repeats async:(BOOL)async {
if (!task || start < 0 || (interval <= 0 && repeats)) return nil;
//创建队列
dispatch_queue_t queue = async ? dispatch_queue_create("timer", DISPATCH_QUEUE_SERIAL) : dispatch_get_main_queue();
//创建定时器
dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
//设置时间
dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, start * NSEC_PER_SEC, interval * NSEC_PER_SEC);
//加锁
dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);
//定时器的唯一标识
NSString *name = [NSString stringWithFormat:@"%lu",(unsigned long)timers.count];
//存放到字典中，还可以使timer产生强引用
timers[name] = timer;
dispatch_semaphore_signal(semaphore_);
//设置回调
dispatch_source_set_event_handler(timer, ^{
task();
if (!repeats) {
//不重复的任务
[self cancelTask:name];
}
});
//启动定时器
dispatch_resume(timer);
return name;
}
+ (NSString *)exeTask:(id)target
selector:(SEL)selector
start:(NSTimeInterval)start
interval:(NSTimeInterval)interval
repeats:(BOOL)repeats async:(BOOL)async {
return [self exeTask:^{
//消除xcode警告
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
[target performSelector:selector];
#pragma clang diagnostic pop
} start:start interval:interval repeats:repeats async:async];
}
+ (void)cancelTask:(NSString *)taskName {
if (taskName.length == 0) return;
dispatch_semaphore_wait(semaphore_, DISPATCH_TIME_FOREVER);
dispatch_source_t timer = timers[taskName];
if (timer) {
dispatch_source_cancel(timer);
[timers removeObjectForKey:taskName];
}
dispatch_semaphore_signal(semaphore_);
}
@end
使用：
self.timerName = [LWTTimer exeTask:^{
NSLog(@"timer-%@",[NSThread currentThread]);
} start:2.0 interval:1.0 repeats:YES async:NO];
//停止定时器
[LWTTimer cancelTask:self.timerName];
