flutteragency-com-handling-events-and-user-input-in-flutter-.pdf

Handling Events and
User Input in Flutter
AUGUST 2, 2023
Table of Contents
1. Understanding User Input and Events
2. Handling Button Taps
Handling Events and User Input
in Flutter
a

This blog article will explore the exciting topic of handling user input and
events in Flutter.
You’ll discover that user interaction is critical to developing exciting and
dynamic Flutter mobile applications as you progress in your app
development journey.
Let’s get down to the very details of how Flutter handles user input and
events so that we can develop responsive, user-friendly apps.
Understanding User
Input and Events
In Flutter, user input is any action a user performs responding to interactions
like tapping buttons, typing text, or scrolling.
On the other side, events are the responses triggered by user input.
To deliver a seamless user experience, you must record these events as a
Flutter developer and manage them accordingly.
Handling Button Taps
The user interface of any application must include buttons. Let’s look at how
the ‘onPressed’ property may be used to manage button taps:
import 'package:flutter/material.dart';
class ButtonTapDemo extends StatelessWidget {
3. Handling Text Input
4. Gestures Handling
5. Handle Slider Changes
6. Handling Checkbox Changes
7. Conclusion
8. Frequently Asked Questions (FAQs)

const ButtonTapDemo({super.key});
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: ElevatedButton(
onPressed: () {
// This function will be called when the
button is tapped
print('Hey There! How are you?');
},
child: const Text('Tap Me'),
),
),
);
}
}
In the above example, when the user taps the button, it will print ‘Hey There!
How are you?’ to the console. Other than the print() function, we can perform
many more actions when the button is tapped like, navigate to another
screen, update the content, etc.
Handling Text Input
The TextField widget can be used to manage user-provided text input. Here
is an example of how to retrieve user input from a text eld:
class TextFieldEventDemo extends StatefulWidget {
const TextFieldEventDemo({super.key});
@override
_TextFieldEventDemoState createState() =>

_TextFieldEventDemoState();
}
class _TextFieldEventDemoState extends State {
String input = '';
@override
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
TextField(
onChanged: (value) {
// This function is called whenever the
user types in the text field
setState(() {
input = value;
});
},
decoration: const InputDecoration(
labelText: 'Write something',
border: OutlineInputBorder(),
),
),
Text(input)
],
),
),
);
}
}
In this example, we have used a StatefulWidget which shows that the
TextField widget takes the input from the user and updates the text below it.
Whenever the user will type in the text eld, the onChange method of the
TextField will be triggered and the state of the text below it will be changed.

Gestures Handling
Flutter has a variety of widgets to handle various gestures, including tapping,
swiping, and dragging.
Let’s look at an illustration of how the GestureDetector widget handles a tap
gesture:
class GestureDetectorDemo extends StatelessWidget {
const GestureDetectorDemo({super.key});
@override
return GestureDetector(
onTap: () {
// This function is called when the user taps
anywhere on the widget
print('Screen tapped!');
},
child: const Scaffold(
body: Center(
child: Text(
'Tap anywhere on the screen',
),
),
),
);
}
}
In this example, we have wrapped the whole screen in the GestureDetector.
So, when the user taps anywhere on the screen, the ‘onTap’ function is
triggered and ‘Screen tapped!’ will be printed in the console.

Handle Slider Changes
Sliders help choose a value from a range. To track and react to changes in
slider value, utilize Flutter’s Slider widget.
class SliderDemo extends StatefulWidget {
const SliderDemo({super.key});
@override
_SliderDemoState createState() => _SliderDemoState();
}
class _SliderDemoState extends State {
int _value = 35;
@override
return Scaffold(
body: Center(
child: Padding(
padding: const EdgeInsets.all(15.0),
child: Center(
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceEvenly,
mainAxisSize: MainAxisSize.max,

children: [
SizedBox(
width: 70,
child: Icon(
Icons.volume_up,
size: _value.toDouble(),
),
),
Expanded(
child: Slider(
value: _value.toDouble(),
min: 10.0,
max: 60.0,
divisions: 10,
activeColor: Colors.deepPurple,
inactiveColor: Colors.orange,
label: _value.toString(),
onChanged: (double newValue) {
setState(() {
_value = newValue.round();
});
},
semanticFormatterCallback: (double
newValue) {
return '${newValue.round()}
dollars';
},
),
),
],
),
),
),
),
);
}
}

In this example, we have a sound icon and a slider next to it, based on the
slider’s value the size of the sound icon will be changed. When the user drags
the slider’s head, the onChanged() function will be triggered and the size of
the sound icon will be changed.
Handling Checkbox
Changes
Binary choices are frequently selected using checkboxes. You can monitor
changes in the checkbox’s state and respond to them using Flutter’s
Checkbox widget.
class CheckBoxDemo extends StatefulWidget {
const CheckBoxDemo({super.key});
@override
_CheckBoxDemoState createState() =>
_CheckBoxDemoState();
}
class _CheckBoxDemoState extends State {
bool? valuefirst = false;
bool? valuesecond = false;
@override
return MaterialApp(
home: Scaffold(
body: SizedBox(
child: Column(

mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.start,
children: [
const Text(
'Checkbox without Header and Subtitle:',
style: TextStyle(fontSize: 15.0),
),
Row(
children: [
Checkbox(
// checkColor: Colors.greenAccent,
// activeColor: Colors.red,
value: valuefirst,
onChanged: (bool? value) {
setState(() {
valuefirst = value;
});
},
),
Text(valuefirst.toString())
],
),
Row(
children: [
Checkbox(
value: valuesecond,
onChanged: (bool? value) {
setState(() {
valuesecond = value;
});
},
),
Text(valuesecond.toString())
],
)
],
)),
),

);
}
}
In this example, there are two checkBoxes whose byDefault value is false and
when tapped, the onChanged() function is triggered and the value of that
particular checkbox is set to true.
Conclusion
Handling user input and events is essential to creating responsive Flutter
applications. Using several Flutter widgets and callbacks, we explored how to
handle button taps, collect text input, detect gestures, respond to checkbox
changes, and handle slider interactions.
Congratulations on mastering the art of using Flutter to handle user input and
events!
Hence, these abilities enable you to develop responsive and responsive and
fascinating apps. Visit www. utteragency.com to stay updated on the latest
Flutter trends, best practices, and development tips.
Frequently Asked
Questions (FAQs)
1. Which widget does Flutter use
for user input?
Flutter uses various widgets to handle user inputs such as, gesture detector,
inkwell, text eld, checkbox, button, etc. The most popular widget for user
input is text eld.
2. How does Flutter handle user
input?

Flutter provides us with a very rich set of widgets and event handling
mechanisms. Using these widgets and event handlers, developers can easily
capture and respond to user input which makes the application user friendly
and responsive.
3. How to Handle User Input and
Events in Flutter?
To manage user input and events in Flutter:
1. Select the appropriate widget based on the desired user input, like
TextField, GestureDetector, InkWell, Checkbox, Radio, Switch, Slider,
DropdownButton, etc.
2. Attach event handlers to widgets that respond to user interactions. These
handlers, or callback functions, execute when the corresponding events
occur.
3. Use the TextField widget to capture textual input. You can provide a
controller to track and manipulate the input and de ne callbacks for text
changes.
By following these steps, you can e ciently handle user input and events in
Flutter, creating a seamless and interactive user experience.
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