Timer class Null safety

A count-down timer that can be configured to fire once or repeatedly.

The timer counts down from the specified duration to 0. When the timer reaches 0, the timer invokes the specified callback function. Use a periodic timer to repeatedly count down the same interval.

A negative duration is treated the same as a duration of 0. If the duration is statically known to be 0, consider using run.

Frequently the duration is either a constant or computed as in the following example (taking advantage of the multiplication operator of the Duration class):

const timeout = const Duration(seconds: 3);
const ms = const Duration(milliseconds: 1);

startTimeout([int milliseconds]) {
  var duration = milliseconds == null ? timeout : ms * milliseconds;
  return new Timer(duration, handleTimeout);
void handleTimeout() {  // callback function

Note: If Dart code using Timer is compiled to JavaScript, the finest granularity available in the browser is 4 milliseconds.

See Stopwatch for measuring elapsed time.


Timer(Duration duration, void callback())
Creates a new timer. [...]
Timer.periodic(Duration duration, void callback(Timer timer))
Creates a new repeating timer. [...]


hashCode int
The hash code for this object. [...]
read-only, inherited
isActive bool
Returns whether the timer is still active. [...]
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
tick int
The number of durations preceding the most recent timer event. [...]


cancel() → void
Cancels the timer. [...]
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
toString() String
Returns a string representation of this object.


operator ==(Object other) bool
The equality operator. [...]

Static Methods

run(void callback()) → void
Runs the given callback asynchronously as soon as possible. [...]