FlutterStepper with ListView content.

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  int _currentStep = 0;
  List<String> documents = ['file1.rst', 'file_2.txt', 'file_3.pdf'];
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'App',
      home: new Scaffold(
        appBar: new AppBar(title: new Text('App')),
        body: new Stepper(
          type: StepperType.vertical,
          currentStep: _currentStep,
          onStepTapped: (int step) => setState(() => _currentStep = step),
          onStepContinue:
              _currentStep < 2 ? () => setState(() => _currentStep += 1) : null,
          onStepCancel:
              _currentStep > 0 ? () => setState(() => _currentStep -= 1) : null,
          steps: <Step>[
            new Step(
              title: new Text('Shipping'),
              content: new Text('This is the first step.'),
              isActive: _currentStep >= 0,
              state:
                  _currentStep >= 0 ? StepState.complete : StepState.disabled,
            ),
            new Step(
              title: new Text('Payment'),
              content: Column(
                children: <Widget>[
                  ListView.builder(
                    shrinkWrap: true,
                    itemCount: documents.length,
                    itemBuilder: (context, index) {
                      final item = documents[index];

                      return ListTile(
                        title: Text("$item"),
                      );
                    },
                  ),
                  Container(
                    child: MouseRegion(
                      child: GestureDetector(
                        child: Icon(
                          Icons.upload_file,
                          color: Colors.grey,
                        ),
                        // onTap: () => {}
                      ),
                    ),
                  )
                ],
              ),
              isActive: _currentStep >= 0,
              state:
                  _currentStep >= 1 ? StepState.complete : StepState.disabled,
            ),
            new Step(
              title: new Text('Order'),
              content: new Text('This is the third step.'),
              isActive: _currentStep >= 0,
              state:
                  _currentStep >= 2 ? StepState.complete : StepState.disabled,
            ),
          ],
        ),
      ),
    );
  }
}