I would like to check if an element exists or not. Something like a function that returns a Boolean. Or something similar to a function in Selenium 'ifExists' which wouldn't throw an exception if the element didn't necessarily exist and it would go about continuing the process without stopping in between when an element isn't found. There are similar things that exist on flutter_test but I have been unable to use it alongside flutter_driver so far.
According to Flutter issue #15852, there is currently no such possibility so far.
But one workaround mentioned in this issue by the user jonsamwell is to use the waitFor method by flutter driver and wrap it in a try/catch to wait if it times out. If it times out, the element is not there, if it does not time out, the element is present:
Future<void> testStep() async {
final isOpen = await isPresent(find.byType("Drawer"), world.driver);
if (isOpen) {
...
}
}
Future<bool> isPresent(SerializableFinder finder, FlutterDriver driver, {Duration timeout = const Duration(seconds: 1)}) async {
try {
await driver.waitFor(finder, timeout: timeout);
return true;
} catch (e) {
return false;
}
}
Obviously, you have to calculate the waiting time according to your use-case to consider any loading times.
try-catch approach didn't work for me.
I have written a peace of code to do the trick for me
Future<bool> isPresent(SerializableFinder finder, FlutterDriver driver, {Duration timeout = const Duration(seconds: 1)}) async {
Stopwatch s = new Stopwatch();
s.start();
await driver.waitFor(finder, timeout: timeout);
s.stop();
if(s.elapsedMilliseconds >= timeout.inMilliseconds){
return false;
}else{
return true;
}
}
Future<void> testStep() async {
final exists = await isPresent(find.byValueKey("accountMenu"), driver);
if (exists ) {
...
}
}
if the time it took for the "driver.waitFor" function to find our widget was more than the timeout, then the widget is not present.
Related
hello I want have to run two functions(Function1() and Function2()) and store value of these returns and run third function. But some time according to condition Function1() or Function2() or both not be run.
if(condition1){
await Function1();
}
if(condition2){
await Function2();
}
await Functon3();
I try as above but Function3() run simultaneously with Function1() or with Function2().
My Function1() code looks like following...
Future Function1() async {
apiService
.apiFileUpload()
.then((value) async {
///codes goes here
}).catchError((error) {
print('EEEE: ' + error.toString());
});
}
If anything not clear please let me know in the comment section.
Please do not use .then() in combination with async/await. It is technically possible, but it takes some skill to get it right, so why make it hard on yourself. Stick with one way of doing it, use either one or the other. You mixed it up and through a slight oversight, your Function1 does not actually wait on it's result. It just returns, with the function still running in the then block. So you await it, but that does not help.
Since you are using await already, stick with that and remove .then() from your repertoire for now:
Future Function1() async {
try {
final value = await apiService.apiFileUpload();
///codes goes here
} catch(error) {
print('EEEE: ' + error.toString());
}
}
You can use await
Future Function1() async {
try{
final value = await apiService
.apiFileUpload();
final value2 = await secondFuntion();
///add more and condition on values
} catch(e){
.....
}
}
from your question you need to tell the compiler to stop on particular task with await and avoid using then function it will never stop your compiler
your future fuction:
Future Function1() async {
apiService
.apiFileUpload()
.then((value) async {
///codes goes here
}).catchError((error) {
print('EEEE: ' + error.toString());
});
}
Modified Future func
Future Function1() async {
var result = await apiService.apiFileUpload();
if(result == success){
// code goes here
}else{
//you can show your error here
}
}
Im having issues with my code and since I'm new at using Flutter, I have no clue on how to fix it. I was trying to fix the http.get(string) and I kind of did, but now I'm having issues with then(()).
void submitForm(FeedbackForm feedbackForm) async {
try {
await http.get(Uri.parse(URL + feedbackForm.toParams()).then((response)) {
callback(convert.jsonDecode(response.body['status']));
});
} catch (e) {
print(e);
}
}
}
It seems you got a parenthesis missplaced:
await http.get(...).then((response) => callback(...))
The them allows you to use the result of the previous Future, as soon as it becomes available. If you find it confusing you can declare one variable at a time.
final response = await http.get(...);
// Check if response was as expected
await callback();
Looking for help here guys. I have 2 Futures that populate data in sqflite. I need one (_insertInitialData()) to finish first before calling the second one (_insertAdditionalData()). I have done it this way, but it's not working. It first does the re-recreation of the DB as expected, then both _insertInitialData() and _insertAdditionalData() not in the order I expected. I have tried .whenComplete and calling here _insertAdditionalData() and also have tried different ways that I think should work but nothing.
This is just something I'm doing for fun but still I'd like to know what I'm doing wrong.
TIA
Future<void> _insertAdditionalData() async{}
void populateDB() {
try {
final localDB = LocalDatabase.instance;
Future.wait([localDB.dropDB(recreateDB: true)]).then((_){
print('DB recreated!');
Future.wait([_insertInitialData()]).then((_) {
print('_insertInitialData done');
Future.wait([_insertAdditionalData()]).then((_){
print('_insertAdditionalData done');
});
});
});
} catch (ex) {
print('There was a problem in populateDB(): $ex');
}
}```
Using await makes things a lot easier to read and will block execution of later lines until the action has finished.
Future<void> populateDB() async {
final localDB = LocalDatabase.instance;
await localDB.dropDB(recreateDB: true);
print('DB recreated!');
await _insertInitialData();
print('_insertInitialData done');
await _insertAdditionalData();
print('_insertAdditionalData done');
}
You can try using only one future statement, and follows it with multiple "then". This makes sure the first "then" will be completed before the second "then" is executed. I assume your localDB.dropDB(recreateDB: true) function is asynchronous.
Future<void> _insertAdditionalData() async{}
void populateDB() {
try {
final localDB = LocalDatabase.instance;
localDB.dropDB(recreateDB: true).then((_){
print('DB recreated!');
}).then((_) {
_insertInitialData();
print('_insertInitialData done');
}).then(() {
_insertAdditionalData();
print('_insertAdditionalData done');
});
} catch (ex) {
print('There was a problem in populateDB(): $ex');
}
}
Cool. Thanks for your comments. I replaced all of those Future.wait for async/await even in my internal methods that insert into the DB and it's all good!!! (executing in the sequence I need)
Just learning Dart/Flutter for fun and I love it.
I want to write a functions which returns until an upload has been finished. If it is possible it would be good if I could also add a timeout.
waitForUpload() async {
uploader.result.listen((result) {
// return waitForUpload
}
}
I just don't find how to write this in dart. To make it more clear: In JS the code would look like this:
async waitForUpload() {
return new Promise((resolve) => {
uploader.result.listen((result) {
resolve();
});
});
}
Using a Completer would be more straightforward.
Future time(int time) async {
Completer c = new Completer();
new Timer(new Duration(seconds: time), (){
c.complete('done with time out');
});
return c.future;
}
Stream.single implements the behavior I want. Looking at implementation, you can see future._complete(result); is called inside the listen method which resolves the future.
getData() async {
http.Response response = await http.get('https://www.example.com/);
print(response.body);
}
The above function works to get the HTML code of a page but it fails in some cases. The function is sometimes never completed and it waits forever to get response( For example, if the app is opened while internet is off and even when its turned on, it never connects). In such situations is there any way to retry ?
I tried the http retry package but it gives me 15+ errors.
Example code for how this could be done:
import 'package:http/http.dart' as http;
import 'dart:convert';
Future<List> loadData() async {
bool loadRemoteDatatSucceed = false;
var data;
try {
http.Response response = await http.post("https://www.example.com",
body: <String, String>{"username": "test"});
data = json.decode(response.body);
if (data.containsKey("success")) {
loadRemoteDatatSucceed = true;
}
} catch (e) {
if (loadRemoteDatatSucceed == false) retryFuture(loadData, 2000);
}
return data;
}
retryFuture(future, delay) {
Future.delayed(Duration(milliseconds: delay), () {
future();
});
}
You can use RetryPolicy from http package to retry your connection, just create your own class and inherit form RetryPolicy and override these function like the following example, then create a Client using HttpClientWithInterceptor.build and add your custom retryPolicy as a parameter, this will retry your request for a number of times until a condition is met, if not, it'll just stop retrying.
import 'package:http/http.dart';
class MyRetryPolicy extends RetryPolicy {
final url = 'https://www.example.com/';
#override
// how many times you want to retry your request.
int maxRetryAttempts = 5;
#override
Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async {
//You can check if you got your response after certain timeout,
//or if you want to retry your request based on the status code,
//usually this is used for refreshing your expired token but you can check for what ever you want
//your should write a condition here so it won't execute this code on every request
//for example if(response == null)
// a very basic solution is that you can check
// for internet connection, for example
try {
final result = await InternetAddress.lookup('google.com');
if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
return true;
}
return false;
} on SocketException catch (_) {
return false;
}
}
}
then create and use a client to make your requests.
it will automatically retry the request if the condition you wrote is met.
Client client = HttpClientWithInterceptor.build(
retryPolicy: ExpiredTokenRetryPolicy(),
);
final response = await client.get('https://www.example.com/);
there is also a package to check for internet connection if that your problem, see connectivity
You can use try-catch blocks inside async functions like you would in synchronous code. Perhaps you'd be able to add some sort of error handling mechanism in the function, and retry the function on error? Here's some documentation on that one.
Example from the docs:
try {
var order = await getUserOrder();
print('Awaiting user order...');
} catch (err) {
print('Caught error: $err');
}
You can also catch specific Exceptions, per this github issue.
doLogin(String username, String password) async {
try {
var user = await api.login(username, password);
_view.onLoginSuccess(user);
} on Exception catch(error) {
_view.onLoginError(error.toString());
}
}
EDIT: This may also help.
While we're at it, look here for a function that reattempts an async operation however many times you need.