async_builder - Improved Future and Stream builder for Flutter.
This package provides
AsyncBuilder, a widget similar to StreamBuilder / FutureBuilder which is designed to reduce
boilerplate and improve error handling.
It also provides
InitBuilder, which makes it easier to start async tasks safely.
How to use
1. Add to dependencies
dependencies: async_builder: ^1.2.0
import 'package:async_builder/async_builder.dart'; import 'package:async_builder/init_builder.dart';
AsyncBuilder<String>( future: myFuture, waiting: (context) => Text('Loading...'), builder: (context, value) => Text('$value'), error: (context, error, stackTrace) => Text('Error! $error'), )
AsyncBuilder<String>( stream: myStream, waiting: (context) => Text('Loading...'), builder: (context, value) => Text('$value'), error: (context, error, stackTrace) => Text('Error! $error'), closed: (context, value) => Text('$value (closed)'), )
Note that you cannot provide both a stream and future.
Instead of a single builder, AsyncBuilder allows you to specify separate builders depending on the state of the asynchronous operation:
waiting(context)- Called when no events have fired yet.
builder(context, value)- Required. Called when a value is available.
error(context, error, stackTrace)- Called if there was an error.
closed(context, value)- Called if the stream was closed.
If any of these are not provided then it defaults to calling
builder (potentially with a null
AsyncBuilder does not silently ignore errors by default.
If an exception occurs and
error is provided, the widget will rebuild and call that builder.
error is not provided and
silent not true then the exception and stack trace will be printed to
console (default behavior).
initial is provided, it is used in place of the value before one is available.
stream is a ValueStream (BehaviorSubject) holding an existing value, that value will be available immediately on
StreamSubscription for this widget can be paused with the
pause parameter, this is useful if you want to notify
StreamController that you don't need updates.
InitBuilder is a widget that initializes a value only when its configuration changes, this is extremely useful because it allows you to safely start async tasks without making a whole new StatefulWidget.
The basic usage of this widget is to make a separate function outside of build that starts the task and then pass it to InitBuilder, for example:
static Future<int> getNumber() async => ...; build(context) => InitBuilder<int>( getter: getNumber, builder: (context, future) => AsyncBuilder<int>( future: future, builder: (context, value) => Text('$value'), ), );
In this case, getNumber is only ever called on the first build.
You may also want to pass arguments to the getter, for example to query shared preferences:
final String prefsKey; build(context) => InitBuilder.arg<String, String>( getter: sharedPrefs.getString, arg: prefsKey, builder: (context, future) => AsyncBuilder<String>( future: future, builder: (context, value) => Text('$value'), ), );
The alternate constructors
InitBuilder.arg7 can be used to pass arguments to the
will re-initialize the value if and only if either
getter or the arguments change.