Flutter墙面涂料用量计算出现空对象赋值错误

报错信息：

The setter 'value=' was called on null.
Receiver: null
Tried calling: value=3000.0

直接点出问题：你只声明了var area;但未初始化，它的默认值是null，当执行area.value = (height * length);时，试图给null的value属性赋值，触发了这个错误。

另外你的判断逻辑也有问题：if (WallheightController.text.isNotEmpty || WalllengthController.text.isNotEmpty )用了逻辑或（||），这意味着只要一个输入框有内容就会进入计算，但此时另一个输入框为空，double.parse会抛出格式错误，应该改成逻辑与（&&）确保两个输入都不为空。

1. 将area初始化为RxDouble类型，和paint、result保持一致：

RxDouble area = 0.0.obs;

2. 修改判断条件为逻辑与：

if (WallheightController.text.isNotEmpty && WalllengthController.text.isNotEmpty )

final WallheightController = TextEditingController();
final WalllengthController = TextEditingController();
var height;
var length;
RxDouble area = 0.0.obs;
RxDouble paint = 0.2.obs;
RxDouble result = 0.0.obs;

calculatepaint() {
  if (WallheightController.text.isNotEmpty &&
      WalllengthController.text.isNotEmpty ) {
     height = double.parse(WallheightController.text);
     length = double.parse(WalllengthController.text);

    area.value = (height * length);
    result.value = area.value * paint.value;

    Get.toNamed(RoutesClass.prcalculation);
   } else {
    Get.snackbar("Fields empty", "Fill Required fields");
  }
}

clear() {
  WallheightController.clear();
  WalllengthController.clear();
}

内容的提问来源于stack exchange，提问作者Huzaifa Arshad