如何在 Flutter 中增加计数器并禁用按钮？

Question

我有一个按钮，我想在增加计数器后禁用它。这是我用来增加计数器的方法：

void incrementAdCounter() async {
    setState(() {
      adCounter++;
      if (adCounter == 2 || adCounter > 2) {
        isAdButtonDisabled = true;
      }
      setAdCounter();
      print(adCounter);
    });
  }

在 initState 内部：

void initButtons() {
    isAdButtonDisabled = false;
    adCounter = 0
}

我有一个按钮，我在 onTap 上调用了这些方法，如果按钮：

void getCounters() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  adCounter = prefs.getInt('adCounter');
  isAdButtonDisabled = prefs.getBool('isAdButtonDisabled');
}
setAdCounter() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setInt('adCounter', adCounter);
    prefs.setBool('isAdButtonDisabled', isAdButtonDisabled);
  }

当我调用此方法时，它显示以下错误：

Unhandled Exception: NoSuchMethodError: The method '+' was called on null.
E/flutter (13166): Receiver: null

Answer 1

int adCounter=0;（随便你先初始化值）

void incrementAdCounter() async {
    setState(() {
      adCounter++;
      if (adCounter == 2 || adCounter > 2) {
        isAdButtonDisabled = true;
      }
      setAdCounter();
      print(adCounter);
    });
  }

Answer 2

对原始代码的这种修改将完全满足您的要求：

int adCounter = 0;

@override
Widget build(BuildContext context) {
  return Center(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text(adCounter.toString()),
        RaisedButton(
          onPressed: adCounter >= 2 ? null : incrementAdCounter,
          child: Text('Increment'),
        ),
      ],
    )
  );
}

void incrementAdCounter() {
  setState(() {
    adCounter++;
  });
}

您的其余代码不需要修改，但如果您的按钮被禁用则您不需要保存到 SharedPreferences。您可以根据值对其进行验证。

Answer 3

试试这个，

void getCounters() async { 
  SharedPreferences prefs = await SharedPreferences.getInstance();
  adCounter = prefs.getInt('adCounter') ?? 0;
  isAdButtonDisabled = prefs.getBool('isAdButtonDisabled'); 
}

如何在 Flutter 中增加计数器并禁用按钮？

How do I increment a counter and disable a button in Flutter?

counter

dart

flutter