CODEWITHSUNDEEP
dart
jmoneystl
jmoneystl

Reputation: 781

How to get a value back from an HttpRequest?

I'm learning Dart and I've hit a roadblock. I very much want to return a value from a json string processing function so I can use that value inside main(). (I'm trying to set some top-level variables to use with a one-way data bind with an html template.) I'm using HttpRequest.getString and a .then call to kick off the processing. But HttpRequest doesn't like being assigned to a variable so I'm not sure how to get anything back out of it.

processString(String jsonString) {
  // Create a map of relevant data
  return myMap;
}

void main() {
  HttpRequest.getString(url).then(processString);
  // Do something with the processed result!
}

I guess my question is how do I get a value back from a function that was called from an HttpRequest?

Upvotes: 1

Views: 623

Answers (1)

Darshan Rivka Whittle
Darshan Rivka Whittle

Reputation: 34031

You're trying to do something that the Dart async model doesn't support. You'll have to handle the result of the async request:

  1. In processString(),
  2. In another function called from processString(),
  3. In an anonymous function passed to then().

Or something similar. What you can't do is access it from further down in main():

processString(String jsonString) {
  // Create a map of relevant data
  // Do something with the processed result!
}

void main() {
  HttpRequest.getString(url).then(processString);
  // Any code here can never access the result of the HttpRequest
}

You may prefer:

processString(String jsonString) {
  // Create a map of relevant data
  return myMap;
}

void main() {
  HttpRequest.getString(url).then((resp) {
    map = processString(resp);
    // Do something with the processed result!
  });
  // Any code here can never access the result of the HttpRequest
}

Upvotes: 2

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