I wanted to make a simple calculator. I wanted to do it all in one function instead of defining functions separately for each operation, but I'm getting an error and I couldn't figure out why I was getting this error.

  late num numberOne, numberTwo;
  String result = '';

  mathFunction(String text) {
    if (textControllerTwo != '0') {
      numberOne = num.tryParse(textControllerOne.text)!;
      numberTwo = num.tryParse(textControllerTwo.text)!;

      switch (text) {
        case 'collection':
          return result = (numberOne   numberTwo).toString();
        case 'interest':
          return result = (numberOne - numberTwo).toString();
        case 'multiply':
          return result = (numberOne * numberTwo).toString();
        case 'divided':
          return result = (numberOne / numberTwo).toString();
      }
    } else {
      return result = 'Number cannot be divided by 0';
    }
    setState(() {});
  }

CodePudding user response：

It is better to get numberOne, numberTwo in methods and make them not optional or use the required annotaiton. make sure textControllerOne.text and textControllerTwo.text and text is not null.

CodePudding user response：

1. Add default clause to your switch statement.
2. Give a default value for each num value from tryParse.
3. Remove setState(() {}); because you must not give a side effect when calling your function/method.
4. No need to use a class/file scope variable (numberOne, numberTwo, result) for your function scope code.
5. Give a return type for your function/method.

here your simplified code:

  // return a string result from mathFunction.
  String mathFunction(String text) {
    if (textControllerTwo != '0') {
      
      // Give 0 if parse failed.
      num numberOne = num.tryParse(textControllerOne.text)??0;
      num numberTwo = num.tryParse(textControllerTwo.text)??0;

      switch (text) {
        case 'collection':
          return (numberOne   numberTwo).toString();
        case 'interest':
          return (numberOne - numberTwo).toString();
        case 'multiply':
          return (numberOne * numberTwo).toString();
        case 'divided':
          return (numberOne / numberTwo).toString();
        default:
          return "ERR"; 
      }
    } else {
      return 'Number cannot be divided by 0';
    }
  }