Dart Futures - Flutter in Focus

What people said

Strong rec Eradicatore · 2021-03 · Stack Overflow · on “Flutter/Dart: can you run a background service with Future.delayed?”

I don't believe there is any risk for memory leaks or crashes, from this anyway. :-) If you haven't watched the flutter videos on async I would highly recommend them. [this video]

Recommends Augustin R · 2019-06 · Stack Overflow · on “Flutter: why ever use a Future over a Stream?”

Why would one ever use a Future? A Future handles a single event when an asynchronous operation completes or fails. It can be used for simple HTTP requests (GET, POST, ...). You can have a look to the boring flutter development show [LINK] where Google engineers build a simple Hacker News app, with Futures. EDIT New video [this video] from Flutter team about dart Futures What disadvantages would using a Stream over a Future have? They are made for different needs : real time updates or asynchronous calls, so they cannot really be compared in terms of advantages of one over the other.

Recommends spenster · 2019-08 · Stack Overflow · on “Questions about Future in Dart”

What triggers/starts a Future execution? The code block for a Future is placed into the event queue, so it's executed when its turn in the event queue comes up. The Flutter in Focus Futures [this video] video has some good visuals about how this works. What's the difference between Future.wait() and Future.then().then().then()? They are different ways of handling multiple futures, but the differences are subtle. Future.wait handles errors slightly differently, and its values are returned as a list rather than in sequential code blocks, but in practice, the difference might not matter for your situation. Are return await myFuture; and return myFuture the same? No. In the first instance, execution

Recommends Marcel · 2019-11 · Stack Overflow · on “Flutter - Best way to request Multiple APIs simultaneously”

Flutter's compute spawns a whole other Isolate (thread-like things in Dart) and that's pretty resource-intensive for just waiting on a network request. Gladly, Dart is event-loop-based, so you can wait on both requests simultaneously by simply wrapping both network request Future s in a call to Future.wait . For more information about Dart's event loop, you might want to check out the explanatory video about Futures on Flutter's YouTube channel [this video] . Future<List<Article>> fetchData() async { var responses = await Future.wait([ http.get(firstUrl), http.get(secondUrl), ]); return <Article>[ ..._getArticlesFromResponse(responses[0]), ..._getArticlesFromResponse(responses[1]), ]; } List<Arti

Recommends Suragch · 2020-02 · Stack Overflow · on “What's the difference between async and async* in Dart?”

Short answer async gives you a Future async* gives you a Stream . async You add the async keyword to a function that does some work that might take a long time. It returns the result wrapped in a Future . Future<int> doSomeLongTask() async { await Future.delayed(const Duration(seconds: 1)); return 42; } You can get that result by awaiting the Future: main() async { int result = await doSomeLongTask(); print(result); // prints '42' after waiting 1 second } async* You add the async* keyword to make a function that returns a bunch of future values one at a time. The results are wrapped in a Stream. Stream<int> countForOneMinute() async* { for (int i = 1; i <= 60; i++) { await Future.delayed(con

Recommends Haidar · 2020-05 · Stack Overflow · on “How to get async value in Flutter”

You are using Future in a wrong way, when you are building a widget that depends on a value from a Future , you need to use FutureBuilder , So for example your _showSearchBar method -which,I assume, you are calling inside build to show something on the screen- will become: Widget _showSearchBar(BuildContext context) { return FutureBuilder( future: getNewsOnSearchBar(), builder: (BuildContext context, AsyncSnapshot snapshot) { if (snapshot.hasData) { if (snapshot.data != null) { return GFSearchBar( // overlaySearchListHeight: 160.0, searchList: list, //empty searchQueryBuilder: (query, list) { return list .where((item) => item.toLowerCase().contains(query.toLowerCase())) .toList(); }, overlay

Recommends Majed DH · 2020-05 · Stack Overflow · on “How to get text off of Flutter Webview Plugin”

From the documentation [LINK] : Use flutterWebviewPlugin.evalJavaScript(String code) . This function must be run after the page has finished loading (i.e. listen to onStateChanged for events where state is finishLoad). If you have a large amount of JavaScript to embed, use an asset file. Actually evalJavaScript returns a Future<String> so you have to await it or use .then( () {} ) . For example: String data_from_webview = await flutterWebviewPlugin.evalJavaScript("document.getElementById('#someElement').innerText"); Here are the documentation [LINK] of Futures and here is a good simple video [this video] about Futures in dart.

Recommends lenz · 2020-09 · Stack Overflow · on “Flutter: RangeError (index): Invalid value: Valid value range is empty: -1”

I recommend you read more on Asynchronous programming: futures, async, await [LINK] . This will save you lots of headaches. There are also amazing videos [this video] from the Flutter team on the topic

Recommends CoderUni · 2020-12 · Stack Overflow · on “Flutter : get Shared Preference items from class into stateless Widget Edit #1”

setState tells the whole screen to rebuild all of its widgets. The print 2 prints null because it didn't wait for Services().get_user().then to finish. Have a look at: [this video] . Learn how to use async and await

Recommends Todd Kerpelman · 2021-02 · Stack Overflow · on “How to get data from Firebase Realtime Database and put it into a list using Flutter?”

The issue you're running into here is that in the first part of the code you're saying, "Hey, Firebase, please retrieve this data and then when you receive it, put it into this variable called list ." But then you're immediately turning around and trying to process list , even before Firebase has had a chance to fill it up. So it's null at the point when you're trying to iterate on it. There are a few ways of fixing this, but I suppose the simplest would simply be to add your list parsing logic into the then clause of your Firebase call. A little something like this... Future<String> sumTimers() async { FirebaseDatabase.instance .reference() .child("Timers") .once() .then((DataSnapshot snaps