update method
Implementation
void update(TextEditingValue newValue) {
if (value == newValue) {
return;
}
value = newValue;
if (SchedulerBinding.instance.schedulerPhase ==
SchedulerPhase.persistentCallbacks) {
SchedulerBinding.instance.addPostFrameCallback(markNeedsBuild);
} else {
markNeedsBuild();
}
}