Custom Stepper in Flutter

#flutter #android #ios #dart

Stepper is a small UI Component but, a most useful component in Application Development to increment or decrement a value. People also call as Counter but, I am calling this has a Stepper because I came from an iOS Development background.

What is a Stepper?

A stepper is a two-buttons used to increase or decrease an incremental value. By default, one button of a stepper displays a plus symbol, and the other displays a minus symbol. These symbols can be replaced with custom images if desired.

Let's Build a Carousels like this:

This is actually what we going to make by the end of this article. Load up your energy and let's get started.

RoundedIconButton

class RoundedIconButton extends StatelessWidget {
  RoundedIconButton({@required this.icon, @required this.onPress, @required this.iconSize});

  final IconData icon;
  final Function onPress;
  final double iconSize;

  @override
  Widget build(BuildContext context) {
    return RawMaterialButton(
      constraints: BoxConstraints.tightFor(width: iconSize, height: iconSize),
      elevation: 6.0,
      onPressed: onPress,
      shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(iconSize*0.2)),
      fillColor: Color(0xFF65A34A),
      child: Icon(
        icon,
        color: Colors.white,
        size: iconSize * 0.8,
      ),
    );
  }
}

Create a StatelessWidget class and name it as RoundedIconButton

Declare the following properties:

  final IconData icon;
  final Function onPress;
  final double iconSize;

icon is an IconData datatype because we can't pass a string for icon name.
onPress property helps to write the functionality of the button.
iconSize is for making the button more dynamic.

We are returning a RawMaterialButton with common properties you see above like constraints, elevation and child etc..

Custom Stepper

Create a StatelessWidget name it as CustomStepper, we need a StatelessWidget because we often change properties of the Class i.e, incrementing or decrementing a value.

// ignore: must_be_immutable
class CustomStepper extends StatefulWidget {
  CustomStepper({
    @required this.lowerLimit,
    @required this.upperLimit,
    @required this.stepValue,
    @required this.iconSize,
    @required this.value,
  });

  final int lowerLimit;
  final int upperLimit;
  final int stepValue;
  final double iconSize;
  int value;

  @override
  _CustomStepperState createState() => _CustomStepperState();
}

class _CustomStepperState extends State<CustomStepper> {

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        RoundedIconButton(
          icon: Icons.remove,
          iconSize: widget.iconSize,
          onPress: () {
            setState(() {
              widget.value =
                  widget.value == widget.lowerLimit ? widget.lowerLimit : widget.value -= widget.stepValue;
            });
          },
        ),
        Container(
          width: widget.iconSize,
          child: Text(
            '${widget.value}',
            style: TextStyle(
              fontSize: widget.iconSize * 0.8,
            ),
            textAlign: TextAlign.center,
          ),
        ),
        RoundedIconButton(
          icon: Icons.add,
          iconSize: widget.iconSize,
          onPress: () {
            setState(() {
              widget.value =
                  widget.value == widget.upperLimit ? widget.upperLimit : widget.value += widget.stepValue;
            });
          },
        ),
      ],
    );
  }
}

Declare the following properties:

lowerLimit property is where you can update the lower limit of the Stepper.
upperLimit property is where you can update the upper limit of the Stepper.
stepValue property is where you can update each step value of the Stepper.
iconSize property which will manage the whole structure of the Stepper.
value property will be updated each time after RoundedIconButton is Clicked.

Follow the steps to create a CustomStepper:

Create a Row with MainAxisAlignment to center
Add two RoundedIconButton's with passing add, remove icons, and functionalities respectively.
Functionalities:
- Increase the value by stepValue when addButton Clicked.
- Decrease the value by stepValue when removeButton Clicked.
- Ternary Operator is the best one to use in this case.
Give a Text label to the value property and place between the icons.

Here you see the actual CustomStepper.

UseCase Example

class StepperScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
      backgroundColor: kPrimaryColor,
      title: Text("Custom Stepper"),
      centerTitle: false,
      ),
      body: SafeArea(
        child: Center(
          child: Container(
            height: 300,
                width: 200,
                decoration: BoxDecoration(
                  color: Colors.white,
                  borderRadius: BorderRadius.circular(8.0),
                  boxShadow: [
                    BoxShadow(
                      color: kShadowColor,
                      offset: Offset(0, 20),
                      blurRadius: 30.0),
                  ]
            ),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              Padding(
                padding: const EdgeInsets.all(8.0),
                child: Container(
                  decoration: BoxDecoration(
                    color: Colors.black.withOpacity(0.04),
                    borderRadius: BorderRadius.circular(8.0),
                  ),
                  child: Padding(
                    padding: const EdgeInsets.all(8.0),
                    child: Image.asset('assets/images/fruit.png',fit: BoxFit.fitWidth,),
                  ),
                ),
              ),
              Padding(
                padding: const EdgeInsets.only(top: 8.0,left: 8.0),
                child: Text('Juicy Strawberry',style: TextStyle(
                  color: Colors.black,
                  fontSize: 18.0,
                ),),
              ),
              Padding(
                padding: const EdgeInsets.only(top: 8.0,left: 8.0),
                child: Row(
                  children: [
                   Text('\$20.40',style: TextStyle(
                     color: Colors.black,
                     fontSize: 15.0,
                     fontWeight: FontWeight.bold,
                   ),), 
                Spacer(),
                CustomStepper()
                  ],
                ),
              ),

            ],
        ),
          )),
      ),
    );
  }
}

I used a simple example of a Grocery Cart where you can add the quantity of the Item through CustomStepper.

Conclusion

Stepper helps to increase and decrease the value easily. Use stepper for small values, for example, How many hour's you sleep per day?. On the other hand, it doesn’t make sense to use a stepper to How many miles you travel per day?.

GitHub Link

If you like to improve your App Development Skills, even more in Flutter and SwiftUI. Feel free to dm me on Instagram or tweet to me on Twitter if you have any additional tips or feedback.

Thanks for reading!