如何在 Dart 中对简单函数进行空值检查？

Question

void main() {
  Car myCar = Car(drive: slowDrive);
  myCar.drive();
}

class Car {
  Car({this.drive});
  Function? drive;
}

void slowDrive() {
  print('Driving slowly');
}

void fastDrive() {
  print('Driving fast');
}

该错误表示，必须先对值可以为 null 的表达式进行 null 检查，然后才能取消引用。

我怎样才能对这个进行空检查？

Answer 1

可以使用以下方法完成.call()

void main() {
  Car myCar = Car(drive: slowDrive);
  myCar.drive?.call();
}

class Car {
  Car({this.drive});
  Function? drive;
}

void slowDrive() {
  print('Driving slowly');
}

void fastDrive() {
  print('Driving fast');
}

call还接受带参数的函数

void main() {
  Car myCar = Car(drive: slowDrive);
  myCar.drive?.call(5);
}

class Car {
  Car({this.drive});
  Function(int)? drive;
}

void slowDrive(int a) {
  print('Driving slowly');
}

void fastDrive(int a) {
  print('Driving fast');
}