使用 Set State 更新变量数据

Question

我正在尝试在应用程序恢复时更新这两个变量，变量是分钟和小时。现在，当我恢复应用程序时，值不会更新。

@override
  void initState() {
    super.initState();
    WidgetsBinding.instance!.addObserver(this);
    dateTimeNow = DateTime.parse('${prefs.getString('startTime')}');
    startedDateTime = DateTime.now();

    minutes = startedDateTime.difference(dateTimeNow).inMinutes % 60;
    hours = startedDateTime.difference(dateTimeNow).inHours;

    if (minutes < 0) {
      minutes = 0;
    }
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    switch (state) {
      case AppLifecycleState.inactive:
        print("Inactive");
        break;
      case AppLifecycleState.paused:
        print("Paused");
        break;
      case AppLifecycleState.resumed:
        print('resumed');
        setState(() { // trying to updated
          minutes = startedDateTime.difference(dateTimeNow).inMinutes % 60;
          hours = startedDateTime.difference(dateTimeNow).inHours;
        });
        break;
    }
  }

Answer 1

请在 didChangeAppLifecycleState() 方法的末尾添加 super.didChangeAppLifecycleState(state);，如下所示：

 void didChangeAppLifecycleState(AppLifecycleState state) {
    switch (state) {
      case AppLifecycleState.inactive:
        print("Inactive");
        break;
      case AppLifecycleState.paused:
        print("Paused");
        break;
      case AppLifecycleState.resumed:
        print('resumed');
        setState(() { // trying to updated
          minutes = startedDateTime.difference(dateTimeNow).inMinutes % 60;
          hours = startedDateTime.difference(dateTimeNow).inHours;
        });
        break;
    }
        super.didChangeAppLifecycleState(state);
  }

并且还覆盖了 dispose 方法：

void dispose() {
    WidgetsBinding.instance!.removeObserver(this);
    super.dispose();
  }

Answer 2

您似乎没有更新 startedDateTime 值。您仅在状态的第一次初始化期间设置它，但您不会在以后更新该值。意思是，即使在使用 didChangeAppLifecycleState 更新您的值之后，startedDateTime 仍然相同，因此 minutes 或 hours 值保持不变。

尝试做这样的事情：

@override
void didChangeAppLifecycleState(AppLifecycleState state) {
  super.didChangeAppLifecycleState(state); // <-- Add this as well
  switch (state) {
    <...>
    case AppLifecycleState.resumed:
      print('resumed');
      setState(() {
        // trying to updated
        startedDateTime = DateTime.now(); // <-- Update the value
        minutes = startedDateTime.difference(dateTimeNow).inMinutes % 60;
        hours = startedDateTime.difference(dateTimeNow).inHours;
      });
      break;
  }
}

使用 Set State 更新变量数据

Update variables data using Set State

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