NSTimer scheduledTimerWithTimeInterval与timerWithTimeInterval、initWithFireDate的区别

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 the timer (and the strong reference it had to the timer), either just before the

invalidate

method
returns or at some later point. Once invalidated, timer objects cannot be reused.