CODEWITHSUNDEEP
dartdart-async
Jorge Garduño
Jorge Garduño

Reputation: 11

Why don't set the var (Dart)

I'm trying this in Dart:

import 'dart:convert';
import 'dart:html';

class testHandler {

  Map parsedJSON;

  testHandler();

  void Initialize(){
    String rawJSON = "core/testConfiguration.json";

    HttpRequest.getString(rawJSON)
    .then((String f) => parsedJSON.from(JSON.decode(f)))
    .catchError((Error e) => print(e.toString()));

    print(parsedJSON);
  }
}

If you see I'm setting parsedJSON in .then() but when I'm trying to get the var, it returns null.

Upvotes: 1

Views: 73

Answers (2)

kelegorm
kelegorm

Reputation: 975

No, you are not setting parsedJSON in .then(). You are trying to call method from null object. Before use parsedJSON you should set it with = operator, like

parsedJSON = new Map.from(JSON.decode(f));

In other words, you mixed up parsedJSON's methods and Map's constructors.

P.S. And, as Gunter denoted it, you may write it shortly:

parsedJSON = JSON.decode(f);

Upvotes: 0

Günter Zöchbauer
Günter Zöchbauer

Reputation: 657506

print(parsedJSON); is executed before getString() returns. getString() is async and the callback passed to then() will be executed sometimes later after getString() returned the result but print(parsedJSON); will be executed immediately.

Using async/await makes this quite easy:

import 'dart:convert';
import 'dart:html';

class testHandler {

  Map parsedJSON;

  testHandler();

  Future Initialize() async {
    String rawJSON = "core/testConfiguration.json";

    try {
      String f = await HttpRequest.getString(rawJSON);
      parsedJSON = JSON.decode(f);
    } catch(Error e) { 
      print(e.toString());
    } 

    print(parsedJSON);
  }
}

Async is contagious therefore code calling Initialize() has to wait for it to finish as well.

Upvotes: 2

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