Flutter StatelessWidget 和 Provider 没有不必要地更新或调用构建

我正在try 使用Provider和Stateless小部件页面来更新倒计时UI.

当我运行以下所有操作时，我会在秒表每1秒的滴答声中在控制台中收到两条打印消息:

例如

flutter: build()
flutter: _buildCountDown()

此外，remaining值实际上不会在UI中更新.

But if I:

• 将页面设为StatefulWidget
• replace the variable access with Consumer<CountdownProvider> syntax 例如

return Consumer<CountdownProvider>(
  builder: (_, countdownProvider, __) {
    return Text(countdownProvider.remaining.toString()),
});

...一切都按预期进行:UI正确更新，我没有得到build()的打印输出，只有_buildCountDown()，这正是我想要的.

Q) What am I doing wrong that means I can't make this a Stateless widget that updates as expected?

1. 主要的dart我有这样的提供者:

return MultiProvider(
  providers: [        
    ChangeNotifierProvider(
      create: (_) => CountdownProvider(),
    ),
  ],
)

2. 我编写了一个简单的倒计时提供者-CountdownProvider:

class CountdownProvider extends ChangeNotifier {

  int remaining = 0;
  final Stopwatch _stopwatch = Stopwatch();
  late Timer _timer;

  void start(int val) {
    remaining = val;
    _timer = Timer.periodic(const Duration(seconds: 1), _onTick);
    _stopwatch.start();
  }

  void _onTick(Timer timer) {
    remaining--;
    if (remaining < 0) {
      return;
    }
    notifyListeners();
  }

  void stop(bool skipNotify) {
    _timer.cancel();
    _stopwatch.stop();

    if (skipNotify) {
      _stopwatch.reset();
      remaining = 0;
      return;
    }
    notifyListeners();
  }
}

3. 显示页面:PageCountdown:

class PageCountdown extends StatelessWidget {
  const PageCountdown({
    Key? key,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    // 10 seconds default countdown
    Provider.of<CountdownProvider>(context, listen: false).start(10);

    print("build()");
    return Scaffold(
      body: _buildContent(context),
    );
  }

  Widget _buildContent(BuildContext context) {
    return SafeArea(
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          _buildCountDown(context),
        ],
      ),
    );
  }

  Widget _buildCountDown(BuildContext context) {
    int remaining = Provider.of<CountdownProvider>(context).remaining;

    print("_buildCountDown()");

    return Text(
      remaining.toString(),
    );
  }
}