Async/Await - Flutter in Focus

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Strong rec Sahil Hariyani · 2022-04 · Stack Overflow · on “How to assign future<String> to a String variable in flutter”

Future<String> getJwt() async {} as getJWT() returns a Future which indicates it will return some value (a String) in the future. This is part of asynchronous programing. So, adding await basically says that we need to wait for the response which will be there at some point in the future. static String token = await getJwt(); You can watch this awesome tutorial on async and wait [this video] by Flutter team

Recommends Xander · 2019-10 · Stack Overflow · on “Still problems with async validations in flutter”

TextFormField expects a synchronous function as a validator (that's an ordinary function that does some task and then returns its result). checkEmail is exactly this, a synchronous function. It sets up a Future which will, in two seconds, set _emailExist to true . But crucially, it doesn't then wait around for two seconds. It immediately returns the current value of _emailExist (which is false the first time it runs). Two seconds later, your Future resolves and sets _emailExist to true. That's why, when you run it the second time, it works as expected ( _checkEmail again returns the current value of _emailExist but this is now true ). One way around this is to provide onChanged and decoratio

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 josxha · 2020-06 · Stack Overflow · on “How to get inside data in Future<Map<dynamic, dynamic>>?”

Your function returnUserMap() returns a Future<Map> . I suspect that the error you describe is not in the code snippet you copied. Whenever the task to be performed may take some time, you will receive a future. You can wait for futures in an async function with await . It is therefore recommended to use a so-called FutureBuilder in your build() function: FutureBuilder<FirebaseUser>( future: _auth.currentUser(), builder: (BuildContext context, AsyncSnapshot snapshot) { if (snapshot.hasData) { final FirebaseUser user = snapshot.data; if (user.displayName == null || user.displayName.isEmpty()) return text(currentUser.email); // display email if name isn't set return text(currentUser.displayNam

Recommends mahesh · 2020-07 · Stack Overflow · on “State does not update until button is pressed twice”

It is because you have async method in your setState method. The setState method will be called synchronously. So here problem is when setState is performed and frame get refreshed your data from api has not arrived yet and it showing you the old data. When you again click the button your out variable have new data (from your first click) which will be shown on the screen and API will be called again. To solve your problem FlatButton( onPressed: () async { FocusScope.of(context).unfocus(); await getPrice(ticker.text); setState(() { }); }, child: Text('Submit') ), So call the setState method after API call is completed. To know more about async/await watch this video : [this video]

Recommends Tirth Patel · 2020-08 · Stack Overflow · on “what is the difference between async and async* in dart?”

Checkout 4th [this video] & 5th [LINK] of the "Flutter in Focus" series by Flutter team. They've explained them pretty well.

Recommends mahesh · 2020-09 · Stack Overflow · on “How would you execute code only if you get a response from an async function?”

There are two methods to achieve this. Use await onTap: () async { bool success = true; try { await loginUser(passwordController.text, nameController.text); } on Exception { success = false; } if(success) { Navigator.push(context, MaterialPageRoute(builder: (context) => Dashboard()) ); } } Use then onTap: () { loginUser(passwordController.text, nameController.text).then((user){ Navigator.push(context, MaterialPageRoute(builder: (context) => Dashboard()) ); }).catchError((error) => handleError(error)); } To get more about Future, async, await: [this video]

Recommends Frank van Puffelen · 2021-12 · Stack Overflow · on “Flutter Firebase getting list of document”

Since you already marked the function as async , you can use await inside it to mask the asynchronicity a bit: Future<List<dynamic>> getProducts2() async { CollectionReference ref = _firestore.collection('Products'); List<Product> productsArray = []; var snapshots = await ref.get() snapshots.forEach((element) { element.docs.forEach((value) { var p = Product.fromSnapshot(value); productsArray.add(p); print("size: " + productsArray.length.toString()); }); }); print("+ size: " + productsArray.length.toString()); return productsArray; } To learn more about futures, and async/await in Flutter: [LINK] . In fact, I'm gonna add the first video [this video] from that search to my playlist as Andrew is a g

Recommends Frank van Puffelen · 2021-12 · Stack Overflow · on “Flutter Null Safety and Firebase authentication error”

You can't return something from within the listen callback to the scope of your user() function. The closest equivalent to what you have now is to return a Future<User?> with something like this: Future<User?> user() { return firebaseAuth.authStateChanges().first() } You have to return a Future here (or mark the function as async , which does pretty much the same thing) because the authStateChanges() comes from Firebase asynchronously, and won't yet be available by the time the return statement runs. I recommend reading up on asynchronous behavior in Flutter/Dart, for example with: Video: Async/Await - Flutter in Focus [this video] Codelab: Asynchronous programming: futures, async, await [LINK]

Recommends Binabh Devkota · 2022-01 · Stack Overflow · on “Type 'Future<dynamic>' is not subtype of type 'Widget'”

You are getting this error because your function _widgetbuilder returns Future<dynamic> because the function is async. Widget _widgetbuilder(){ // code here } The function should be in this structure to return of type Widget . The code that needs to be async should either be taken out of build function or use .then pattern for async code instead of async await if you really need to. This short 9 min video [this video] will help you understand async better in flutter.