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.
Related
There are some questions posted about uploading multiple files to Firebase, but all the solutions I came across use a forEach loop or something similar to upload one by one. However, if I'm uploading files that depend on each other (say, my app requires both of them to exist to function correctly), this could be an issue because one of the uploads could succeed and the other fail.
I thought there must be a way to do something similar to a batch write in Firestore but for uploading files in Firebase Storage.
Is there any way to do that or is the loop method the only way?
(I'm using Flutter, so if possible I would appreciate it if any code provided as an answer is written in Dart)
Well, you could use Future.wait() to upload your files simultaneously without waiting for any of them to complete before you begin other.
To explain further, I made the following code snippet, please follow along:
void main() {
Future.wait([
uploadImage1(),
uploadImage2(),
uploadImage3(),
]);
}
Future<void> uploadImage1() async {
await Future.delayed(Duration(seconds: 3), () {
print('1');
});
}
Future<void> uploadImage2() async {
throw Exception();
}
Future<void> uploadImage3() async {
await Future.delayed(Duration(seconds: 3), () {
print('3');
});
}
I made three async operations, and added them all to Future.wait list, so all are executed/triggered at the same time, doesn't matters if any of them fails. Try the code on dart pad and you will see the output appears at the same time, the output would look like:
1
3
: ExceptionError: Exception
On the other hand, if you want to wait for one operation to successfully finish, then you can use await on a method that returns Future, so it will wait until the operation is successfully completed.
void main() async {
await uploadImage1();
await uploadImage2();
await uploadImage3();
}
Future<void> uploadImage1() async {
await Future.delayed(Duration(seconds: 3), () {
print('1');
});
}
Future<void> uploadImage2() async {
throw Exception();
}
Future<void> uploadImage3() async {
await Future.delayed(Duration(seconds: 3), () {
print('3');
});
}
The output would be:
1
: ExceptionError: Exception
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();
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.
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.