Stopwatch#

A stopwatch which measures time while it's running.

A stopwatch is either running or stopped. It measures the elapsed time that passes while the stopwatch is running.

When a stopwatch is initially created, it is stopped and has measured no elapsed time.

The elapsed time can be accessed in various formats using elapsed, elapsedMilliseconds, elapsedMicroseconds or elapsedTicks.

The stopwatch is started by calling start.

Example:

final stopwatch = Stopwatch();
print(stopwatch.elapsedMilliseconds); // 0
print(stopwatch.isRunning); // false
stopwatch.start();
print(stopwatch.isRunning); // true

To stop or pause the stopwatch, use stop. Use start to continue again when only pausing temporarily.

stopwatch.stop();
print(stopwatch.isRunning); // false
Duration elapsed = stopwatch.elapsed;
await Future.delayed(const Duration(seconds: 1));
assert(stopwatch.elapsed == elapsed); // No measured time elapsed.
stopwatch.start(); // Continue measuring.

The reset method sets the elapsed time back to zero. It can be called whether the stopwatch is running or not, and doesn't change whether it's running.

// Do some work.
stopwatch.stop();
print(stopwatch.elapsedMilliseconds); // Likely > 0.
stopwatch.reset();
print(stopwatch.elapsedMilliseconds); // 0

Constructors#

Stopwatch()#

Creates a Stopwatch in stopped state with a zero elapsed count.

The following example shows how to start a Stopwatch immediately after allocation.

final stopwatch = Stopwatch()..start();

Stopwatch() {
  _frequency; // Ensures initialization before using any method.
}

Properties#

elapsed no setter#

The elapsedTicks counter converted to a Duration.

Duration get elapsed {
  return Duration(microseconds: elapsedMicroseconds);
}

elapsedMicroseconds no setter#

The elapsedTicks counter converted to microseconds.

external int get elapsedMicroseconds;

elapsedMilliseconds no setter#

The elapsedTicks counter converted to milliseconds.

external int get elapsedMilliseconds;

elapsedTicks no setter#

The elapsed number of clock ticks since calling start while the Stopwatch is running.

This is the elapsed number of clock ticks between calling start and calling stop.

Is 0 if the Stopwatch has never been started.

The elapsed number of clock ticks increases by frequency every second.

int get elapsedTicks {
  return (_stop ?? _now()) - _start;
}

frequency no setter#

Frequency of the elapsed counter in Hz.

int get frequency => _frequency;

hashCode no setter inherited#

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

external int get hashCode;

isRunning no setter#

Whether the Stopwatch is currently running.

bool get isRunning => _stop == null;

runtimeType no setter inherited#

A representation of the runtime type of the object.

Inherited from Object.

external Type get runtimeType;

Methods#

noSuchMethod() inherited#

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

reset()#

Resets the elapsed count to zero.

This method does not stop or start the Stopwatch.

void reset() {
  _start = _stop ?? _now();
}

start()#

Starts the Stopwatch.

The elapsed count increases monotonically. If the Stopwatch has been stopped, then calling start again restarts it without resetting the elapsed count.

If the Stopwatch is currently running, then calling start does nothing.

void start() {
  int? stop = _stop;
  if (stop != null) {
    // (Re)start this stopwatch.
    // Don't count the time while the stopwatch has been stopped.
    _start += _now() - stop;
    _stop = null;
  }
}

stop()#

Stops the Stopwatch.

The elapsedTicks count stops increasing after this call. If the Stopwatch is currently not running, then calling this method has no effect.

void stop() {
  _stop ??= _now();
}

toString() inherited#

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

external String toString();

Operators#

operator ==() inherited#

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

external bool operator ==(Object other);