FlutterSlider range onDragging Missing parameter type

Question

I am trying to use FlutterSlider (another_xlider). The following code in the IDE is flagging both lowerValue and upperValue with Missing parameter type. I am prompted to try adding an explicit type, or remove implicit-dynamic from your analysis options file. The latter I am loathe to do. I have tried the former, but am apparently getting it wrong.

Here is my current code.

                            values: const [1000, 4000],
                            rangeSlider: true,
                            max: 10000,
                            min: 500,
                            onDragging: (handlerIndex, lowerValue, upperValue) {
                              _lowerValue = lowerValue is int ? lowerValue : 0;
                              _upperValue = upperValue is int ? upperValue : 0;
                              setState(() {});
                            },
                          )

If I try setting an explicit type as below, I get The argument type 'Null Function(int, int, int)' can't be assigned to the parameter type 'dynamic Function(int*, dynamic, dynamic)

                              _lowerValue = lowerValue;
                              _upperValue = upperValue;
                              setState(() {});
                            },
                          )

The function signature is dynamic Function(int*, dynamic, dynamic)*. I need to research what those asterisks mean - having only used them with yield statements - so I presume that is part of the issue.

FWIW - This is nearly identical to the example in the another_xlider documentation at https://pub.dev/packages/another_xlider/example (sample below).

  values: [30, 420],
  rangeSlider: true,
  max: 500,
  min: 0,
  onDragging: (handlerIndex, lowerValue, upperValue) {
    _lowerValue = lowerValue;
    _upperValue = upperValue;
    setState(() {});
  },
)

Googling has not helped thus far. What am I missing?

UPDATE I created my project using Very Good Cli (see https://verygood.ventures/blog/flutter-starter-app-very-good-core-cli). While trying to debug, I pulled down the another_xlider project and the problem was not presenting. I created a brand new project using Very Good Cli, copied over the MyApp class, and the problem was presenting again. So, I copied over all the dependencies in the Very Good project to my non-VGC project and updated. No problem. It appears there is something fundamental about the way a VGC project is created that is causing the problem. However, as time is of the essence and in the meantime having found the built-in Flutter RangeSlider fills my needs, I am no longer concerned about this. That said, I would like to know what it is with Very Good Cli that caused this problem. Next time there might not be an easy alternative.

Answer 1

I just took a look at it looks like the onDragging callback indicates lowerValue and upperValue are of type dynamic (https://github.com/loonix/another_xlider/blob/7fa4c15a4362d25ecf8e2552e27e5799024c715f/lib/another_xlider.dart#L27). As a result, you need to both specify the dynamic type explicitly to avoid the implicit_dynamic issue and also cast the value as a double (if you are sure it should be a double). The following code reports no analysis errors with the latest version of very_good_cli:

onDragging: (
  handlerIndex,
  dynamic lowerValue,
  dynamic upperValue,
) {
  setState(() {
    _lowerValue = lowerValue as double;
    _upperValue = upperValue as double;
  });
},

Answer 2

Despite the fact that in the documentation to the version 3.4.0 mentioned that

Since version 3.4.0-dev.3, step type is no longer double, its FlutterSliderStep

seems like the latest dev update is still not in public, so lowerValue and upperValue are still double types. So just define two properties before creating slider and use it inside of the onDragging: function:

double _lowerValue;
double _upperValue;
...
FlutterSlider(
      ...
      onDragging: (handlerIndex, lowerValue, upperValue) {
        _lowerValue = lowerValue;
        _upperValue = upperValue;
        setState(() {});
      },
      ...
    );