Please upvote: https://github.com/dart-lang/sdk/issues/40198
I am wondering how I can get access to the value of a future, while debugging in vs-code? Right now i need to introduce another temp variable to get the debugger to await the statement. This is how I am accessing a value at the moment:
Future<void> disconnect2() async {
var conn = await isConnected;
if (conn) await internalDisconnect();
}
But I would like to write the following:
Future<void> disconnect() async {
if (await isConnected) await internalDisconnect();
}
And still be able to access the value of isConnected with the debugger.
What I tried so far:
Try to add the expression (await isConnected) to the watch.
Tried to evaluate the expression (await isConnected) in the debug console.
Try to add the expression isConnected to the watch.
Tried to evaluate the expression isConnected in the debug console.
Tried to access the value through hovering over the instance. In the screenshot it is null, but most of the time I get to access only the future object.
Is there any easy way to access the value of a future while debugging?
You cannot see the value of future value while it is not awaited and loaded. The reason for it, future type is waiting the data, so it reserve part of memory for future value. You can access it only after getting the value f.e. value from REST API.
You can use then method and see the value there.
someFuture(arg).then((erg) => print(erg));
Related
I am using flutter with the cbl package to persist data. Trying to retrieve the entries does not seem to work because the function created is returning at the await statement and not the return statement. This does not seem like the intended result of darts async/await functionality. So I am lost.
task_database.dart
Future<dynamic> getAllTasks() async {
final tasksDb = await Database.openAsync(database); <---------- Returns here
var tasksQuery = const QueryBuilder()
.select(SelectResult.all())
.from(DataSource.database(tasksDb));
final resultSet = await tasksQuery.execute();
late var task;
await for (final result in resultSet.asStream()) {
final map = result.toPlainMap();
final taskDao = TaskDao.fromJson(map);
task = taskDao.task;
// Do something with the task...
print(task);
}
;
return task; <-------------------------------------------- Does not make it here
}
task_cubit.dart
getAllTasks() => {
allTaskMap = TasksAbcDatabase().getAllTasks(),
emit(TaskState(tasks: state. Tasks))
};
What I have tried. I have tried to use Database.openSync instead of Database.openAsync however, the function just returns at the next await statement. I have also tried making getAllTasks asynchronous and awaiting the database as such.
Future<void> getAllTasks() async => {
allTaskMap = await TasksAbcDatabase().getAllTasks(),
emit(TaskState(tasks: state. Tasks))
};
However this has the same issue, when the function from task_database returns prematurely it the returns at the first await function in getAllTasks which is the allTaskMap variable.
Thanks
A function cannot "return prematurely" without a return statement.
The only way the execution is cut short would be an exception being thrown.
I also don't see how you don't get syntax errors, when you don't await the Database.openAsync(database) statement.
So make sure all your awaits are in place. Use the linter to find those that are missing. While you are at it, remove the keyword dynamic from your vocabulary, it will only hurt you if you use it without a need for it. Your return type should be properly typed, then your compiler could tell you, that returning a single task from a function that is clearly supposed to return multiple tasks is not going to work.
Either catch your exceptions and make sure you know there was one, or do not catch them and watch them go all the way through into your debugger.
In addition, following the comment of #jamesdlin, your function definitions are... valid, but probably not doing what you think they are doing.
Future<void> getAllTasks() async => {
allTaskMap = await TasksAbcDatabase().getAllTasks(),
emit(TaskState(tasks: state. Tasks))
};
needs to be
Future<void> getAllTasks() async {
allTaskMap = await TasksAbcDatabase().getAllTasks();
emit(TaskState(tasks: state. Tasks));
}
I am trying to get Contact using the function getContactsForPhone
getName()async{
number = '123-456-7890'
return await ContactsService.getContactsForPhone(number).then((value) => value.elementAt(0).displayName.toString());
}
but I am getting Future<dynmaic> instead of .displayName which is supposed to be String
You are mixing it up two way's to use Futures:
You can use await keyword to await for the conclusion.
You can use the then method to have a callback when the Future ends.
You need to choose one and stick with it. Using the await is always preferable because it makes the code more readable and avoids some callback hells.
In your case:
Future<String> getName() async {
number = '123-456-7890'
Iterable<Contact> myIterable = await ContactsService.getContactsForPhone(number);
List<Contact> myList = myIterable.toList();
return myList[0].displayName.toString()
}
Which should return the DisplayName you wanted.
Remember to also use the await keyword from the outside, wherever you call this function.
You can read more about Future and Asynchronous code here.
Help is much appreciated how to trace down this issue, because I am running out of ideas.
I am calling the function getOrderCollection, below, but it aborts after the first line var myCompanyDoc = await FirebaseFirestore.instance.collection('companies').doc(myCompany).get(); Without trowing anything to the console or jumping into some library when debugging. When I click next statement it jumps back to the calling function.
I am authenticated to the database, companyCollection = FirebaseFirestore.instance.collection('companies') provides an initialized object pointing to the collection and myCompany is a constant with the document id entered by copy/paste.
If some rules for the database but I can't see successful or denied queries with the monitor.
Any ideas how I can proceed tracing down the issue?
Future<void> getOrderCollection() async {
var myCompanyDoc = await FirebaseFirestore.instance.collection('companies').doc(myCompany).get();
print("companyDoc fetched");
final myDeliveryDocRef = myCompanyDoc.data()['delivery'].toString();
orderCollection = FirebaseFirestore.instance.collection('companies').doc(myCompany).collection('features').doc(myDeliveryDocRef).collection('orders');
orderBriefDoc = FirebaseFirestore.instance.collection('companies').doc(myCompany).collection('features').doc(myDeliveryDocRef);
}
UPDATE: This is collection > document what corresponds to final String myCompany = '4U4kZKXkr3rHA6B04S5K';
As we discussed in your comments, the issue was that you forgot to await the getOrderCollection() function. Even though, as you mentioned, your caller function _deliveryRepository.initRepository() was awaited, you still had to await getOrderCollection() inside your caller method to make sure that the code is waiting for the getOrderCollection() to be executed before it proceeds to the next line.
In general, you want to have some error handling and to type the known types/classes (avoid using var).
Error handling - for async/await place the code inside a try/catch.
Typing - Dart is type safe, which is really great to prevent runtime errors.
Depending on your setup, you might be able to hover over the Firestore.instance.collection(...).doc(...) to see the return type. .doc(...).get() returns a DocumentSnapshot and .collection(...).get() returns a CollectionSnapshot.
Using the above, it should be easier to debug:
Future<void> getOrderCollection() async {
try {
DocumentSnapshot myCompanyDoc = await FirebaseFirestore.instance.collection('companies').doc(myCompany).get();
print("companyDoc fetched");
final myDeliveryDocRef = myCompanyDoc.data()['delivery'].toString();
} catch(e) {
print('Error: ' + e.toString());
}
}
Don't forget to await your other 2 Firestore queries.
I'm having some problems with a line in the function below. The function is handling async gets from Firebase Storage. I'm using it to get the names and urls of files I have stored there.
The issues is with getting the Urls. Specifically on the line:
String url = element.getDownloadURL().toString();
getDownloadedURL() is a Firebase future. I tried to await it, but it won't recognise the await, I guess due to "element".
The over all effect is that when I'm using this in my UI via a Future builder, the name comes out fine but the Url doesn't. It is being retrieved as the print statement shows it. But it's not being waited for, so the UI is already updated.
Been trying lots of things, but haven't found a solution, so any help would be greatly appreciated.
Future<void> getImageData() async {
final imagesFromStorage = await fb
.storage()
.refFromURL('gs://little-big-deals.appspot.com')
.child('images')
.listAll();
imagesFromStorage.items.forEach((element) {
print(element.name);
String url = element.getDownloadURL().toString();
print(url.toString());
imageData.add(ImageData(element.name, url.toString()));
});
}
Many thanks
You can't use async in forEach.
Just use a for loop:
Future<void> getImageData() async {
final imagesFromStorage = await fb
.storage()
.refFromURL('gs://little-big-deals.appspot.com')
.child('images')
.listAll();
for (var element in imagesFromStorage.items) {
print(element.name);
String url = (await element.getDownloadURL()).toString();
print(url.toString());
imageData.add(ImageData(element.name, url.toString()));
}
}
Soo, the title might be a bit confusing but let me clear that up right now.
I have a class called UserController which has a method called updateUserData. It gets a Map<String, dynamic> and updates the given attributes of a user with whatever is given in the value of the map.
What I wanted to do is: Send a patch request to the server, wait for the server to return a changed user object, write that to some local variable and return either the value or the error to whoever called that method (which in my case is a GUI class).
The current method as it is:
Future<User> updateUserData(Map<String, dynamic> changes) async {
return await http.patch(
"url",
headers: {HttpHeaders.authorizationHeader: "token"},
body: changesMap
).then((newUserObject) => {
currentUser = newUserObject;
//return new user object for display
}); //error from server gets forwarded to GUI.
}
Sadly this doesn't work at all. Seems like Flutter/dart doesn't know what to return there (it gives me a return_of_invalid_type_from_closure error).
I hope it's clear what my goal was. I want to use a "then" clause in this method but then still return a future which either contains the user I get from the server or the error I get.
How do I do that? I looked up so many Future tutorials so far and none used something similar.
You never need to use async/await with then. In your case, the simplest thing to do is await the response of your request, and then, put it to your local variable.
Then you just need to return the value.
Future<User> updateUserData(Map<String, dynamic> changes) async {
final response = await http.patch(
"url",
headers: {HttpHeaders.authorizationHeader: "token"},
body: changesMap,
);
// You need to parse the response to get your User object.
final responseJson = json.decode(response.body);
newUserObject = User.fromJson(responseJson);
currentUser = newUserObject;
return newUserObject;
}
If you need to decode your Map to a Class, you can see the answer given here