In Dart, you can make a function that returns Future if you need to perform asynchronous activities. Some of the time, you might need to build a Flutter widget that relies upon the consequence of a Future. All things considered, you can utilize FutureBuilder. FutureBuilder is a widget that utilizes the result of a Future to build itself. The following are instances of how to utilize the widget.
In this blog, we will be Explore FutureBuilder In Flutter. We will also implement a demo program and we show you how to use FutureBuilder in your flutter applications.
Table Of Contents::
Introducton:
In Flutter, the FutureBuilder Widget is utilized to make widgets dependent on the most recent snapshot of association with a Future. Future needs to be gotten before either through a difference in state or change in dependencies. FutureBuilder is a Widget that will assist you with executing some asynchronous function and based on that function’s outcome your UI will update.
In future builder, it calls the future capacity to wait for the outcome, and when it creates the outcome it calls the builder function where we assemble the widget.
Constructor:
To utilize FutureBuilder, you need to call the constructor underneath:
const FutureBuilder({
Key? key,
Future<T>? future,
T? initialData,
required AsyncWidgetBuilder<T> builder,
})
The FutureBuilder class has a conventional parameter which is the information type to be returned by the Future. To utilize it, you need to call the constructor which can be seen previously. Fundamentally, what you need to do is construct a widget utilizing a capacity passed as the builder the contention, because of the snapshot of a Future, passed as the future argument.
Parameters:
There are some parameters of FutureBuilderare:
Key? key: The widget’s key, used to control how a widget is replaced with another widget.Future<T>? future: AFuturewhose snapshot can be accessed by thebuilderfunction.T? initialData: The data that will be used to create the snapshots until a non-nullFuturehas completed.required AsyncWidgetBuilder<T> builder: The build strategy used by this builder.
How to implement code in dart file :
You need to implement it in your code respectively:
Let’s create a Future:
To start with, we need to make a Future to be passed as the future argument. In this article, we will utilize the capacity beneath, which returns Future<String>
Future<String> getValue() async {
await Future.delayed(Duration(seconds: 3));
return 'Flutter Devs';
}
You should be cautious when passing the Future. In the event that you pass it as the code underneath.
FutureBuilder(
future: getValue(),
// other arguments
),
The getValue function will be considered each time the widget is reconstructed. If you don’t need the function to be considered each time the widget is revamped, you should not make the Future inside State.build or StatelessWidget.build technique. TheFuture should be made before, for instance during State.initState, State.didChangeDependencies, or State.daidUpdateWidget. In the model underneath, the Future is put away in a state variable.
Future<String> _value;
@override
initState() {
super.initState();
_value = getValue();
}
Then, at that point, pass the state variable as the future argument.
FutureBuilder<String>(
future: _value(),
// other arguments
),
Let’s create a AsyncWidgetBuilder
You are needed to pass an AsyncWidgetBuilder function that is utilized to assemble the widget. The function has two boundaries. The main boundary’s sort is BuildContext, while the subsequent boundary’s sort is AsyncSnapshot<T>. You can utilize the value of the subsequent boundary to decide the substance that ought to be delivered.
In the first place, you need to comprehend about AsyncSnapshot. AsyncSnapshot is portrayed as a changeless portrayal of the latest interaction with an asynchronous calculation. For this situation, it addresses the most recent communication with a Future. There are some significant properties AsyncSnapshot that can be helpful. The first is connectionState whose type is ConnectionState enum. It shows the current association state to an asynchronous calculation. In the FutureBuilder’s degree, the asynchronous calculation is the Future.
FutureBuilder<String>(
future: _value,
builder: (
BuildContext context,
AsyncSnapshot<String> snapshot,
) {
if (snapshot.connectionState == ConnectionState.waiting) {
return CircularProgressIndicator();
} else if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
return const Text('Error');
} else if (snapshot.hasData) {
return Text(
snapshot.data,
style: const TextStyle(color: Colors.cyan, fontSize: 36)
);
} else {
return const Text('Empty data');
}
} else {
return Text('State: ${snapshot.connectionState}');
}
},
),
The enum has some possible values:
- > none: Not connected to any asynchronous computation. It can happen if the
futureis null. - > waiting: Associated with asynchronous calculation and awaiting communication. In this specific situation, it implies the Future hasn’t been finished.
- > active: Associated with a functioning asynchronous calculation. For instance, if a Stream has returned any value yet is not finished at this point. Ought not to occur for FutureBuilder.
- > done: Associated with an ended asynchronous calculation. In this unique circumstance, it implies the Future has finished.
Another property you need to know is hasError. It tends to be utilized to show whether the depiction contains a non-null error value. If the last consequence of the asynchronous activity was fizzled, the value will be valid. To check whether the snapshot contains non-null information, you can utilize the hasData property.
The asynchronous activity must be finished with non-null information altogether for the value to turn out to be valid. Nonetheless, if the asynchronous activity finishes without information (for example Future<void>), the value will be false. If the snapshot has data, you can acquire it by getting to the data property.
Because of the value of the properties above, you can figure out what ought to be delivered on the screen. In the code over, a CircularProgressIndicator is shown when the connectionState value is waiting. At the point when the connectionState changes to done, you can check whether the snapshot has an error or data.
Let set the Initial Data:
The constructor of FutureBuilder has a named parameter initialData. It very well may be utilized to pass the data that will be utilized to make the snapshots until a non-null Future has finished. Passing a value as the initialData makes the hasData property have true value toward the start, even before the Future finishes.
You can get to the initial data utilizing the data property. When the Future has finished with a non-invalid value, the value of data will be supplanted with another worth returned by the Future. If the Future finishes with an error, the hasData and data properties will be refreshed to false and invalid individually.
FutureBuilder<String>(
initialData: 'Demo Name'
// other arguments
),
By setting an initial data, the snapshot can have information in any event, when the connection state is as yet waiting. In this manner, we need to change the code above inside the if (snapshot.connectionState == ConnectionState.waiting) block, with the goal that the initial data can be shown when the association state is waiting.
if (snapshot.connectionState == ConnectionState.waiting) {
return Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.center,
children: [
CircularProgressIndicator(),
Visibility(
visible: snapshot.hasData,
child: Text(
snapshot.data,
style: const TextStyle(color: Colors.black, fontSize: 24),
),
)
],
);
}
When we run the application, we ought to get the screen’s output like the underneath screen video.
Code File:
import 'package:flutter/material.dart';
import 'package:flutter_futurebuilder_demo/splash_screen.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Splash(),
debugShowCheckedModeBanner: false,
);
}
}
Future<String> getValue() async {
await Future.delayed(Duration(seconds: 3));
return 'Flutter Devs';
}
class FutureBuilderDemo extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _FutureBuilderDemoState ();
}
}
class _FutureBuilderDemoState extends State<FutureBuilderDemo> {
Future<String> _value;
@override
initState() {
super.initState();
_value = getValue();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
automaticallyImplyLeading: false,
backgroundColor: Colors.black,
title: const Text('Flutter FutureBuilder Demo'),
),
body: SizedBox(
width: double.infinity,
child: Center(
child: FutureBuilder<String>(
future: _value,
initialData: 'Demo Name',
builder: (
BuildContext context,
AsyncSnapshot<String> snapshot,
) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.center,
children: [
CircularProgressIndicator(),
Visibility(
visible: snapshot.hasData,
child: Text(
snapshot.data,
style: const TextStyle(color: Colors.black, fontSize: 24),
),
)
],
);
} else if (snapshot.connectionState == ConnectionState.done) {
if (snapshot.hasError) {
return const Text('Error');
} else if (snapshot.hasData) {
return Text(
snapshot.data,
style: const TextStyle(color: Colors.cyan, fontSize: 36)
);
} else {
return const Text('Empty data');
}
} else {
return Text('State: ${snapshot.connectionState}');
}
},
),
),
),
);
}
}
Conclusion:
In the article, I have explained the basic structure of the FutureBuilder in a flutter; you can modify this code according to your choice. This was a small introduction to FutureBuilder On User Interaction from my side, and it’s working using Flutter.
I hope this blog will provide you with sufficient information on Trying up the FutureBuilder in your flutter projects. We will show you what the Introduction is?. Show a constructor and parameters of Streambuilder. That is the way to utilize FutureBuilder in Flutter. You need to make a Future and pass it as the future argument. The snapshots of the Future will be passed to the builder function, in which you can decide the format to be shown depending on the current snapshot. So please try it.
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