Flutter – Pass a Function as an Argument From One Screen to Another
In Flutter, you can pass a function as an argument from one screen (widget) to another screen (widget) by defining a callback function and passing it as an argument when navigating or pushing to the new screen. Here’s a step-by-step guide on how to do this:
Required Tools
To build this app, you need the following items installed on your machine:
- Visual Studio Code / Android Studio
- Android Emulator / iOS Simulator / Physical Device device.
- Flutter Installed
- Flutter plugin for VS Code / Android Studio.
A sample video is given below to get an idea about what we are going to do in this article.
Step By Step Implementations
Step 1: Create a New Project in Android Studio
To set up Flutter Development on Android Studio please refer to Android Studio Setup for Flutter Development, and then create a new project in Android Studio please refer to Creating a Simple Application in Flutter.
Step 2: Import the Package
First of all import material.dart file.
import 'package:flutter/material.dart';
Step 3: Execute the main Method
Here the execution of our app starts.
Dart
void main() { runApp(MyApp()); } |
Step 4: Create MyApp Class
In this class we are going to implement the MaterialApp , here we are also set the Theme of our App.
Dart
class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( debugShowCheckedModeBanner: false , theme: ThemeData( primarySwatch: Colors.green, // Set the app's primary theme color ), home: FirstScreen(), ); } } |
Step 5: Create FirstScreen Class
In this class, we are going to implement a scaffold to display our UI, and Here we are also declaring the callback function and navigate the second screen by passing the callback funtion to its constructor.
Dart
class FirstScreen extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text( 'First Screen' )), body: Center( child: ElevatedButton( onPressed: () { // Navigate to the SecondScreen when the button is pressed Navigator.push( context, MaterialPageRoute( builder: (context) => SecondScreen(callback: sayHello), ), ); }, child: Text( 'Go to Second Screen' ), ), ), ); } // Callback function to be passed to the SecondScreen String sayHello() { return "Hello From the First Screen" ; } } |
Step 6: Create SecondScreen Class
In this class we are going to call the callback method from the FirstScreen and display a hello message in the SecondScreen.
Dart
class SecondScreen extends StatefulWidget { final Function callback; SecondScreen({required this .callback}); @override _SecondScreenState createState() => _SecondScreenState(); } class _SecondScreenState extends State<SecondScreen> { String message = "" ; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text( 'Second Screen' )), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text( 'Welcome to the Second Screen' ), ElevatedButton( onPressed: () { // Execute the callback function and update the message setState(() { message = widget.callback(); }); }, child: Text( 'Say Hello' ), ), Text( message, style: TextStyle(fontWeight: FontWeight.bold, fontSize: 20), ), // Display the message here ], ), ), ); } } |
Here is the complete code of the above article:
Dart
import 'package:flutter/material.dart' ; void main() { runApp(MyApp()); } class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp( debugShowCheckedModeBanner: false , theme: ThemeData( primarySwatch: Colors.green, // Set the app's primary theme color ), home: FirstScreen(), ); } } class FirstScreen extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text( 'First Screen' )), body: Center( child: ElevatedButton( onPressed: () { // Navigate to the SecondScreen when the button is pressed Navigator.push( context, MaterialPageRoute( builder: (context) => SecondScreen(callback: sayHello), ), ); }, child: Text( 'Go to Second Screen' ), ), ), ); } // Callback function to be passed to the SecondScreen String sayHello() { return "Hello From the First Screen" ; } } class SecondScreen extends StatefulWidget { final Function callback; SecondScreen({required this .callback}); @override _SecondScreenState createState() => _SecondScreenState(); } class _SecondScreenState extends State<SecondScreen> { String message = "" ; @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text( 'Second Screen' )), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Text( 'Welcome to the Second Screen' ), ElevatedButton( onPressed: () { // Execute the callback function and update the message setState(() { message = widget.callback(); }); }, child: Text( 'Say Hello' ), ), Text( message, style: TextStyle(fontWeight: FontWeight.bold, fontSize: 20), ), // Display the message here ], ), ), ); } } |
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