getter 'isNull' 被调用为 null

Question

我在执行以下 flutter 代码时使用了 getx 和 getstorage 包。我想检查一个变量是否为空，但是出现以下错误。执行以下代码时，名为 variable 的变量未存储在磁盘上。

Exception has occurred. NoSuchMethodError (NoSuchMethodError: The getter 'isNull' was called on null. Receiver: null Tried calling: isNull)

screen.dart

TextButton(
  onPressed: () {
    var _variable =  userStorage.read('variable');
    print('_variable = $_variable'); 
    // above prints _variable = null
    if(_variable.isNull){
      // do something if its null
      // but results in flutter error
    }
    else{
      // do something else
    }
  },
  child: Obx(() => (Text(
    'variable value='+controller.variable.value,
  )
  )
  )
)

controller.dart

class Controller extends GetxController {
  var userStorage = GetStorage();
}

Answer 1

如果为空则使用默认值

var _variable =  userStorage.read('variable') ?? "notSet";
if(_variable == "notSet"){
  // do something 
}
else{
  // do something else
}

getter 'isNull' 被调用为 null

The getter 'isNull' was called on null

flutter

flutter-getx