createTicker method
Creates a ticker with the given callback.
The kind of ticker provided depends on the kind of ticker provider.
Implementation
@override
Ticker createTicker(TickerCallback onTick) {
_tickers ??= <_WidgetTicker>{};
final _WidgetTicker result = _WidgetTicker(
onTick,
this,
debugLabel: kDebugMode ? "created by ${describeIdentity(this)}" : null,
);
_tickers!.add(result);
return result;
}