| Inherits from | |
| Conforms to | |
| Framework | /System/Library/Frameworks/Foundation.framework |
| Availability | Available in Mac OS X v10.0 and later. |
| Declared in | NSTimer.h |
| Companion guides | |
| Related sample code |
You use the NSTimer class to create timer objects or, more simply, timers. A timer waits until a certain time interval has elapsed and then fires, sending a specified message to a target object. For example, you could create an NSTimer object that sends a message to a window, telling it to update itself after a certain time interval.
Timers work in conjunction with run loops. To use a timer effectively, you should be aware of how run loops operate—see NSRunLoop and Threading Programming Guide. Note in particular that run loops retain their timers, so you can release a timer after you have added it to a run loop.
A timer is not a real-time mechanism; it fires only when one of the run loop modes to which the timer has been added is running and able to check if the timer’s firing time has passed. Because of the various input sources a typical run loop manages, the effective resolution of the time interval for a timer is limited to on the order of 50-100 milliseconds. If a timer’s firing time occurs during a long callout or while the run loop is in a mode that is not monitoring the timer, the timer does not fire until the next time the run loop checks the timer. Therefore, the actual time at which the timer fires potentially can be a significant period of time after the scheduled firing time.
NSTimer objects are “toll-free bridged” with their Core Foundation counterparts, the CFRunLoopTimerRef type. This means that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. Therefore, in a method where you see an NSTimer * parameter, you can pass a CFRunLoopTimerRef, and in a function where you see a CFRunLoopTimerRef parameter, you can pass an NSTimer instance (you cast one type to the other to suppress compiler warnings). See Interchangeable Data Types for more information on toll-free bridging. For more information about Core Foundation timers, see CFRunLoopTimer Reference.
You specify whether a timer is repeating or non-repeating at creation time. A non-repeating timer fires once and then invalidates itself automatically, thereby preventing the timer from firing again. By contrast, a repeating timer fires and then reschedules itself on the same run loop.
A repeating timer always schedules itself based on the scheduled firing time, as opposed to the actual firing time. For example, if a timer is scheduled to fire at a particular time and every 5 seconds after that, the scheduled firing time will always fall on the original 5 second time intervals, even if the actual firing time gets delayed. If the firing time is delayed so far that it passes one or more of the scheduled firing times, the timer is fired only once for that time period; the timer is then rescheduled, after firing, for the next scheduled firing time in the future.
A timer object can be registered in only one run loop at a time, although it can be added to multiple run loop modes within that run loop. There are three ways to create a timer:
Use the scheduledTimerWithTimeInterval:invocation:repeats: or scheduledTimerWithTimeInterval:target:selector:userInfo:repeats: class method to create the timer and schedule it on the current run loop in the default mode.
Use the timerWithTimeInterval:invocation:repeats: or timerWithTimeInterval:target:selector:userInfo:repeats: class method to create the timer object without scheduling it on a run loop. (After creating it, you must add the timer to a run loop manually by calling the addTimer:forMode: method of the corresponding NSRunLoop object.)
Allocate the timer and initialize it using the initWithFireDate:interval:target:selector:userInfo:repeats: method. (After creating it, you must add the timer to a run loop manually by calling the addTimer:forMode: method of the corresponding NSRunLoop object.)
Once scheduled on a run loop, the timer fires at the specified interval until it is invalidated. A non-repeating timer invalidates itself immediately after it fires. However, for a repeating timer, you must invalidate the timer object yourself by calling its invalidate method. Calling this method requests the removal of the timer from the current run loop; as a result, you should always call the invalidate method from the same thread on which the timer was installed. Invalidating the timer immediately disables it so that it no longer affects the run loop. The run loop then removes and releases the timer, either just before the invalidate method returns or at some later point. Once invalidated, timer objects cannot be reused.
+ scheduledTimerWithTimeInterval:invocation:repeats:
+ scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:
+ timerWithTimeInterval:invocation:repeats:
+ timerWithTimeInterval:target:selector:userInfo:repeats:
– initWithFireDate:interval:target:selector:userInfo:repeats:
Creates and returns a new NSTimer object and schedules it on the current run loop in the default mode.
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds invocation:(NSInvocation *)invocation repeats:(BOOL)repeats
The number of seconds between firings of the timer. If seconds is less than or equal to 0.0, this method chooses the nonnegative value of 0.1 milliseconds instead.
The invocation to use when the timer fires. The timer instructs the invocation object to retain its arguments.
If YES, the timer will repeatedly reschedule itself until invalidated. If NO, the timer will be invalidated after it fires.
A new NSTimer object, configured according to the specified parameters.
After seconds seconds have elapsed, the timer fires, invoking invocation.
NSTimer.hCreates and returns a new NSTimer object and schedules it on the current run loop in the default mode.
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats
The number of seconds between firings of the timer. If seconds is less than or equal to 0.0, this method chooses the nonnegative value of 0.1 milliseconds instead.
The object to which to send the message specified by aSelector when the timer fires. The target object is retained by the timer and released when the timer is invalidated.
The message to send to target when the timer fires. The selector must have the following signature:
- (void)timerFireMethod:(NSTimer*)theTimer |
The timer passes itself as the argument to this method.
The user info for the timer. The object you specify is retained by the timer and released when the timer is invalidated. This parameter may be nil.
If YES, the timer will repeatedly reschedule itself until invalidated. If NO, the timer will be invalidated after it fires.
A new NSTimer object, configured according to the specified parameters.
After seconds seconds have elapsed, the timer fires, sending the message aSelector to target.
NSTimer.hCreates and returns a new NSTimer object initialized with the specified invocation object.
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)seconds invocation:(NSInvocation *)invocation repeats:(BOOL)repeats
The number of seconds between firings of the timer. If seconds is less than or equal to 0.0, this method chooses the nonnegative value of 0.1 milliseconds instead
The invocation to use when the timer fires. The timer instructs the invocation object to retain its arguments.
If YES, the timer will repeatedly reschedule itself until invalidated. If NO, the timer will be invalidated after it fires.
A new NSTimer object, configured according to the specified parameters.
You must add the new timer to a run loop, using addTimer:forMode:. Then, after seconds have elapsed, the timer fires, invoking invocation. (If the timer is configured to repeat, there is no need to subsequently re-add the timer to the run loop.)
NSTimer.hCreates and returns a new NSTimer object initialized with the specified object and selector.
+ (NSTimer *)timerWithTimeInterval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats
The number of seconds between firings of the timer. If seconds is less than or equal to 0.0, this method chooses the nonnegative value of 0.1 milliseconds instead.
The object to which to send the message specified by aSelector when the timer fires. The target object is retained by the timer and released when the timer is invalidated.
The message to send to target when the timer fires. The selector must have the following signature:
- (void)timerFireMethod:(NSTimer*)theTimer |
The timer passes itself as the argument to this method.
Custom user info for the timer. The object you specify is retained by the timer and released when the timer is invalidated. This parameter may be nil.
If YES, the timer will repeatedly reschedule itself until invalidated. If NO, the timer will be invalidated after it fires.
A new NSTimer object, configured according to the specified parameters.
You must add the new timer to a run loop, using addTimer:forMode:. Then, after seconds seconds have elapsed, the timer fires, sending the message aSelector to target. (If the timer is configured to repeat, there is no need to subsequently re-add the timer to the run loop.)
NSTimer.hCauses the receiver’s message to be sent to its target.
- (void)fire
You can use this method to fire a repeating timer without interrupting its regular firing schedule. If the timer is non-repeating, it is automatically invalidated after firing, even if its scheduled fire date has not arrived.
NSTimer.hReturns the date at which the receiver will fire.
- (NSDate *)fireDate
The date at which the receiver will fire. If the timer is no longer valid, this method returns the last date at which the timer fired.
Use the isValid method to verify that the timer is valid.
NSTimer.hInitializes a new NSTimer object using the specified object and selector.
- (id)initWithFireDate:(NSDate *)date interval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats
The time at which the timer should first fire.
For a repeating timer, this parameter contains the number of seconds between firings of the timer. If seconds is less than or equal to 0.0, this method chooses the nonnegative value of 0.1 milliseconds instead.
The object to which to send the message specified by aSelector when the timer fires. The target object is retained by the timer and released when the timer is invalidated.
The message to send to target when the timer fires. The selector must have the following signature:
- (void)timerFireMethod:(NSTimer*)theTimer |
The timer passes itself as the argument to this method.
Custom user info for the timer. The object you specify is retained by the timer and released when the timer is invalidated. This parameter may be nil.
If YES, the timer will repeatedly reschedule itself until invalidated. If NO, the timer will be invalidated after it fires.
The receiver, initialized such that, when added to a run loop, it will fire at date and then, if repeats is YES, every seconds after that.
You must add the new timer to a run loop, using addTimer:forMode:. Upon firing, the timer sends the message aSelector to target. (If the timer is configured to repeat, there is no need to subsequently re-add the timer to the run loop.)
NSTimer.hStops the receiver from ever firing again and requests its removal from its run loop.
- (void)invalidate
This method is the only way to remove a timer from an NSRunLoop object. The NSRunLoop object removes and releases the timer, either just before the invalidate method returns or at some later point.
If it was configured with target and user info objects, the receiver releases its references to those objects as well.
You must send this message from the thread on which the timer was installed. If you send this message from another thread, the input source associated with the timer may not be removed from its run loop, which could prevent the thread from exiting properly.
NSTimer.hReturns a Boolean value that indicates whether the receiver is currently valid.
- (BOOL)isValid
YES if the receiver is still capable of firing or NO if the timer has been invalidated and is no longer capable of firing.
NSTimer.hResets the firing time of the receiver to the specified date.
- (void)setFireDate:(NSDate *)date
The new date at which to fire the receiver. If the new date is in the past, this method sets the fire time to the current time.
You typically use this method to adjust the firing time of a repeating timer. Although resetting a timer’s next firing time is a relatively expensive operation, it may be more efficient in some situations. For example, you could use it in situations where you want to repeat an action multiple times in the future, but at irregular time intervals. Adjusting the firing time of a single timer would likely incur less expense than creating multiple timer objects, scheduling each one on a run loop, and then destroying them.
You should not call this method on a timer that has been invalidated, which includes non-repeating timers that have already fired. You could potentially call this method on a non-repeating timer that had not yet fired, although you should always do so from the thread to which the timer is attached to avoid potential race conditions.
NSTimer.hReturns the receiver’s time interval.
- (NSTimeInterval)timeInterval
The receiver’s time interval. If the receiver is a non-repeating timer, returns 0 (even if a time interval was set).
NSTimer.hReturns the receiver's userInfo object.
- (id)userInfo
The receiver's userInfo object.
Do not invoke this method after the timer is invalidated. Use isValid to test whether the timer is valid.
+ scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:+ timerWithTimeInterval:target:selector:userInfo:repeats:– invalidateNSTimer.hLast updated: 2009-10-19
