Timers的替代方法
如果只是要延迟消息的发送,可以使用NSObject的方法
- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay
- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait
+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget
创建Timer的三种方法
1.scheduling a timer with the current run loop
2.creating a timer that you later register with a run loop
3.initializing a timer with a given fire date
Scheduled Timers
以下两个方法自动注册新创建的timer到当前NSRunLoop对象,NSRunLoop的模式为默认的NSDefaultRunLoopMode
- + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds invocation:(NSInvocation *)invocation repeats:(BOOL)repeats
- + (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInforepeats:(BOOL)repeats
- - (IBAction)startOneOffTimer:sender {
- [NSTimer scheduledTimerWithTimeInterval:2.0
- target:self
- selector:@selector(targetMethod:)
- userInfo:[self userInfo]
- repeats:NO];
- }
重复发送消息
注:创建重复发送消息的timer一般需要保存一个引用,因为需要在某个时刻停止发送消息
- - (IBAction)startRepeatingTimer:sender {
- NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.5
- target:self selector:@selector(timerFireMethod:)
- userInfo:[self userInfo] repeats:YES];
- self.repeatingTimer = timer;
- }
Unscheduled Timers
创建未注册的timer,使用时调用addTimer:forMode注册到NSRunLoop对象
- timerWithTimeInterval:target:selector:userInfo:repeats:
- timerWithTimeInterval:invocation:repeats:
- - (IBAction)createUnregisteredTimer:sender {
- NSMethodSignature *methodSignature = [self methodSignatureForSelector:@selector(invocationMethod:)];
- NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
- [invocation setTarget:self];
- [invocation setSelector:@selector(invocationMethod:)];
- NSDate *startDate = [NSDate date];
- [invocation setArgument:&startDate atIndex:2];
- NSTimer *timer = [NSTimer timerWithTimeInterval:0.5 invocation:invocation repeats:YES];
- self.unregisteredTimer = timer;
- }
- - (IBAction)startUnregisteredTimer:sender {
- if (unregisteredTimer != nil) {
- NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
- [runLoop addTimer:unregisteredTimer forMode:NSDefaultRunLoopMode];
- }
- }
Initializing a Timer with a Fire Date
创建一个拥有指定发送日期的timer
- - (IBAction)startFireDateTimer:sender {
- NSDate *fireDate = [NSDate dateWithTimeIntervalSinceNow:1.0];
- NSTimer *timer = [[NSTimer alloc] initWithFireDate:fireDate
- interval:0.5
- target:self
- selector:@selector(countedtargetMethod:)
- userInfo:[self userInfo]
- repeats:YES];
- timerCount = 1;
- NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
- [runLoop addTimer:timer forMode:NSDefaultRunLoopMode];
- [timer release];
- }
Stopping a Timer
- - (IBAction)stopRepeatingTimer:sender {
- [repeatingTimer invalidate];
- self.repeatingTimer = nil;
- }
- 也可以从timer发送的消息中停止timer
- - (void)countedtargetMethod:(NSTimer*)theTimer {
- NSDate *startDate = [[theTimer userInfo] objectForKey:@"StartDate"];
- NSLog(@"Timer started on %@; fire count %d", startDate, timerCount);
- timerCount++;
- if (timerCount > 3) {
- [theTimer invalidate];
- }
- }
Memory Management
1. The run loop maintains the timer that is registered to it.
2. The timer is passed as an argument when you specify its method as a selector
3. You should maintain a strong reference to the unscheduled timer, in order to ensure that it's not deallocated before you use it.
4. A timer maintains a strong reference to its user info dictionary,
5. A timer maintains a strong reference to its target, so you should make sure that your timer's target survive longer than the timer itself.