NSTimer

NSTimer is a class in the Foundation framework of Apple's Cocoa and Cocoa Touch APIs that allows for the scheduling of timer events. It is used to perform a specific action repeatedly at a given interval or once after a specified delay. Timers are essential for tasks that need to happen periodically, such as updating a user interface, performing background processing, or managing game loops.

To create an NSTimer, you typically use one of its class methods, such as scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:. This method creates a timer and immediately adds it to the current run loop. The target is the object that will receive the timer message, and the selector is the method to be called when the timer fires. The repeats parameter, a boolean, determines if the timer should fire only once or repeatedly.

Once a timer is created and scheduled, it will fire according to its configuration. It is crucial to invalidate timers when they are no longer needed using the invalidate method. This prevents memory leaks and ensures that the timer's target object is not retained indefinitely. Failing to invalidate timers can lead to unexpected behavior and performance issues, especially in applications with a long lifespan.

NSTimer relies on the run loop to operate. The run loop processes input events and schedules tasks, including timer events. When an NSTimer fires, its associated selector is invoked on the target object within the context of the current thread's run loop. If a timer is not added to a run loop, it will not fire. Therefore, it's common practice to use the scheduledTimerWithTimeInterval class methods, which automatically add the timer to the current run loop.