object query and remove parentheses in dart, flutter

问题

Hello? I'm building an app using the flutter provider pattern. And I created a process to query the values ​​inside the object. I also have data in my model dart file.

Check the code below.

List<Device> _devices = [
    Device(one: 'apple', two: 'iphone'),
    Device(one: 'samsung', two: 'galaxy')
];


String Query(String value) {
    return _media.where((medium) => medium.one == value)
                    .map((medium) => (medium.two)).toString();

Query("apple")

So, when I call that function, I expect iphone to be returned. But the results come in (iphne). Actually I know why. After all, the data returned is a List<Device> type. But what I want is to remove the parentheses by returning only the first value in the queried list(meaning only queried list, not the full list). In other words, I want to receive iphone, not (iphone). Currently, I am using substring removing the first and the final word, which seems to have some limitations. Is there any way to remove parentheses in that logic?

回答1:

You have parentheses because you're calling .toString() on a list:

return _media.where((medium) => medium.one == value)
  .map((medium) => (medium.two))
  .toString();

To return just .two or the first found object, you just have to do:

return _media.firstWhere(
  (medium) => medium.one == value, orElse: () => null)?.two;

That will return the value of .two of the first found object or null if nothing found.

Doc: Iterable.firstWhere()

来源：https://stackoverflow.com/questions/60386200/object-query-and-remove-parentheses-in-dart-flutter