Dart: Timer

Carlos Costa

Timer class is a countdown that can be used to schedule a single event or repeated events.

Timer(Duration(seconds: 1), () {
  print('Hello, World!');
});

In the previous example we are creating a timer that will execute the function after 1 second. Timers are non-blocking and run on a different thread.

We also can schedule a repeated event:

Timer.periodic(Duration(seconds: 1), (timer) {
  print('Hello, World!');
});

In this case, the function will be executed every second.

A timer can be started and canceled:

Timer timer = Timer.periodic(Duration(seconds: 1), (timer) {
  print("timer is running");
});

timer.cancel();

🕒 Duration

Duration is a class that represents a time span.

Duration(seconds: 1);
Duration(minutes: 1);
Duration(hours: 1);
Duration(days: 1);

We can apply some math operations to a duration:

var d = Duration(seconds: 30);
d = d + Duration(seconds: 30);

print(d.inMinutes); // 1

Here, we are adding 30 seconds to the duration and then converting it to minutes.

Another example:

var d = Duration(seconds: 30);
d = d * 2;

print(d.inSeconds); // 60

We also can specify the hour, minute, second and millisecond:

var time = Duration(hours: 1, minutes: 30, seconds: 30, milliseconds: 30);
print(time.inSeconds); // 5430
print(time.inMinutes); // 90
print(time.inHours); // 1
print(time.inMilliseconds); // 5430030

And create a negative duration:

var x = Duration(seconds: -30);
var y = Duration(minutes: 1, seconds: 30);
var z = y + x;

print(z.inSeconds); // 60

In the previous example we are creating a negative duration and then adding it to another duration.

Durations can be compared:

var x = Duration(seconds: 30);
var y = Duration(minutes: 1, seconds: 30);

print(x < y); // true
print(x > y); // false
print(x == y); // false

//using compareTo method
print(x.compareTo(y)); // -1

compareTo: returns -1 if x is shorter than y, 0 if x and y are equal, and 1 if x is longer than y.

StopWatch

Stopwatch is a class that measures elapsed time.

var watch = Stopwatch();

watch.start();

print('Stopwatch started');

for (var i = 0; i < 1000000000; i++) {
  //do nothing
}

watch.stop();

print('Stopwatch stopped');

print('Time elapsed: ${watch.elapsedMilliseconds} milliseconds');
// Time elapsed: 246 milliseconds

print('Time elapsed: ${watch.elapsed.inSeconds} seconds');
// Time elapsed: 0 seconds

print('Time elapsed: ${watch.elapsed.inMinutes} minutes');
// Time elapsed: 0 minutes

🕒 Duration

StopWatch

References