debugAssertNoTransientCallbacks method

bool debugAssertNoTransientCallbacks(
  1. String reason

Asserts that there are no registered transient callbacks; if there are, prints their locations and throws an exception.

A transient frame callback is one that was registered with scheduleFrameCallback.

This is expected to be called at the end of tests (the flutter_test framework does it automatically in normal cases).

Call this method when you expect there to be no transient callbacks registered, in an assert statement with a message that you want printed when a transient callback is registered:

  'A leak of transient callbacks was detected while doing foo.'

Does nothing if asserts are disabled. Always returns true.


bool debugAssertNoTransientCallbacks(String reason) {
  assert(() {
    if (transientCallbackCount > 0) {
      // We cache the values so that we can produce them later
      // even if the information collector is called after
      // the problem has been resolved.
      final int count = transientCallbackCount;
      final Map<int, _FrameCallbackEntry> callbacks = Map<int, _FrameCallbackEntry>.of(_transientCallbacks);
        exception: reason,
        library: 'scheduler library',
        informationCollector: () => <DiagnosticsNode>[
          if (count == 1)
            // TODO(jacobr): I have added an extra line break in this case.
              'There was one transient callback left. '
              'The stack trace for when it was registered is as follows:',
              'There were $count transient callbacks left. '
              'The stack traces for when they were registered are as follows:',
          for (final int id in callbacks.keys)
            DiagnosticsStackTrace('── callback $id ──', callbacks[id]!.debugStack, showSeparator: false),
    return true;
  return true;