Flutter中类内静态方法调用实例函数报错，如何修复？

编译时出现如下错误提示：

Instance members can't be accessed from a static method.
Try removing the reference to the instance member, or removing the keyword 'static' from the method.

报错代码如下：

class AddEventsToAllCalendars {
  static void addEvent(Events event) {
    Add2Calendar.addEvent2Cal(buildEvent(event)); <<<< ERROR HERE
  }

  Event buildEvent(Events event) {
    Frequency freq = Frequency.yearly;

    if (event.frequency == 'daily') {
      freq = Frequency.daily;
    } else if (event.frequency == 'weekly') {
      freq = Frequency.weekly;
    } else if (event.frequency == 'monthly') {
      freq = Frequency.monthly;
    }

    return Event(
      title: event.eventName!,
      description: event.eventDescription,
      location: event.location,
      startDate: event.eventDate!,
      endDate: event.eventStartTime!
          .add(Duration(minutes: int.parse(event.eventDuration!))),
      allDay: event.allDay,
      recurrence: Recurrence(
        frequency: freq,
        endDate: event.recurrenceEndDate,
      ),
    );
  }
}

错误原因是静态方法addEvent直接调用了实例方法buildEvent，静态方法属于类本身，无法直接访问类的实例成员，以下是三种可行的修复方式：

方式一：将buildEvent改为静态方法 #

既然addEvent是静态方法，直接把buildEvent也声明为静态方法，静态方法之间可以直接调用：

class AddEventsToAllCalendars {
  static void addEvent(Events event) {
    Add2Calendar.addEvent2Cal(buildEvent(event)); // 可正常调用
  }

  // 新增static关键字
  static Event buildEvent(Events event) {
    Frequency freq = Frequency.yearly;

    if (event.frequency == 'daily') {
      freq = Frequency.daily;
    } else if (event.frequency == 'weekly') {
      freq = Frequency.weekly;
    } else if (event.frequency == 'monthly') {
      freq = Frequency.monthly;
    }

    return Event(
      title: event.eventName!,
      description: event.eventDescription,
      location: event.location,
      startDate: event.eventDate!,
      endDate: event.eventStartTime!
          .add(Duration(minutes: int.parse(event.eventDuration!))),
      allDay: event.allDay,
      recurrence: Recurrence(
        frequency: freq,
        endDate: event.recurrenceEndDate,
      ),
    );
  }
}

方式二：实例化类后调用buildEvent #

如果不想修改buildEvent的静态属性，在静态方法内先创建类的实例，再通过实例调用方法：

class AddEventsToAllCalendars {
  static void addEvent(Events event) {
    // 先创建类实例
    final helper = AddEventsToAllCalendars();
    Add2Calendar.addEvent2Cal(helper.buildEvent(event)); // 通过实例调用方法
  }

  Event buildEvent(Events event) {
    // 方法内容保持不变
    Frequency freq = Frequency.yearly;

    if (event.frequency == 'daily') {
      freq = Frequency.daily;
    } else if (event.frequency == 'weekly') {
      freq = Frequency.weekly;
    } else if (event.frequency == 'monthly') {
      freq = Frequency.monthly;
    }

    return Event(
      title: event.eventName!,
      description: event.eventDescription,
      location: event.location,
      startDate: event.eventDate!,
      endDate: event.eventStartTime!
          .add(Duration(minutes: int.parse(event.eventDuration!))),
      allDay: event.allDay,
      recurrence: Recurrence(
        frequency: freq,
        endDate: event.recurrenceEndDate,
      ),
    );
  }
}

方式三：移除addEvent的static关键字 #

如果该方法不需要作为静态方法使用，直接去掉static关键字，调用时先实例化类再调用方法：

class AddEventsToAllCalendars {
  // 移除static关键字
  void addEvent(Events event) {
    Add2Calendar.addEvent2Cal(buildEvent(event)); // 实例方法间可直接调用
  }

  Event buildEvent(Events event) {
    // 方法内容保持不变
    Frequency freq = Frequency.yearly;

    if (event.frequency == 'daily') {
      freq = Frequency.daily;
    } else if (event.frequency == 'weekly') {
      freq = Frequency.weekly;
    } else if (event.frequency == 'monthly') {
      freq = Frequency.monthly;
    }

    return Event(
      title: event.eventName!,
      description: event.eventDescription,
      location: event.location,
      startDate: event.eventDate!,
      endDate: event.eventStartTime!
          .add(Duration(minutes: int.parse(event.eventDuration!))),
      allDay: event.allDay,
      recurrence: Recurrence(
        frequency: freq,
        endDate: event.recurrenceEndDate,
      ),
    );
  }
}

// 调用示例
final calendarHelper = AddEventsToAllCalendars();
calendarHelper.addEvent(yourEventInstance);

内容的提问来源于stack exchange，提问作者LostTexan