notifyDependents method

@protected void notifyDependents()

Notifies the dependents of a change.

The notification goes through didChangeDependencies, which can only run while a frame is being built. The only way left is therefore to mark the element dirty and notify the dependents from performRebuild.

Implementation

@protected
void notifyDependents() {
  _notifyPending = true;

  // Any build, not this element's own. `markNeedsBuild()` on an element that
  // is building right now does nothing: the framework's assertion lets the
  // self case through, and `if (dirty) return;` swallows the call. On an
  // element that is *not* the one building, the same call is refused
  // outright -- "setState() or markNeedsBuild() called during build" -- and
  // that is what a model touched from the build of a descendant used to
  // get. It is the same ordinary user code either way: a lazy load, a
  // default filled in on first read. Asking for the rebuild after the frame
  // is what turns a lost or refused notification into a late one.
  if (_isRebuilding || SchedulerBinding.instance.isBuilding) {
    // One callback while one is pending, not one per notification. The flag
    // above is what the callback acts on, so a second notification arriving
    // before the frame is over is already carried by the first, and a
    // callback of its own would find nothing left to do.
    if (_notifyDeferred) {
      return;
    }
    _notifyDeferred = true;

    SchedulerBinding.instance
      // The build may be one `runApp` drives outside a frame, and then
      // nothing has asked for the frame this callback needs.
      ..scheduleFrame()
      ..addPostFrameCallback((_) {
        _notifyDeferred = false;
        if (mounted && _notifyPending) {
          markNeedsBuild();
        }
      });
  } else {
    markNeedsBuild();
  }
}