CODEWITHSUNDEEP
flutterasynchronousdartfuture
Panossa
Panossa

Reputation: 395

How do I use Futures in Futures in Flutter?

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.

Upvotes: 0

Views: 312

Answers (1)

siega
siega

Reputation: 2887

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

Upvotes: 1

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