CountdownTimer

A CountdownTimer is a timer component that counts down from a defined duration to zero. It typically emits a completion signal when the countdown ends and can also provide periodic tick events to report the remaining time.

Key properties include the total duration, the current remaining time, and the running state. Core methods usually include start, pause, resume, reset, and cancel. A countdown often uses a tick interval to update listeners, and when the remaining time reaches zero, a completion callback is invoked. Some implementations offer a single-shot countdown, while others can be configured to restart after finishing.

Common use cases include user interfaces that require a limited time to perform an action, such as a cooldown for resending a verification code, timed quizzes or games, workout timers, and other scenarios that need to track how much time remains before an event occurs.

Implementation considerations focus on accuracy and resource management. To minimize drift, many designs compute an end time by adding the duration to the start timestamp and derive the remaining time from the current time on each tick. Using a precise time source and avoiding cumulative decrements can help keep the countdown accurate. Threading and synchronization details vary by platform; it is important to handle cancellation, pause, and resume without leaking resources and to recalculate end times appropriately when the timer is paused.

See also: timer, stopwatch, interval timer.