Flex developers, embrace Promise!

LucaSimone — Sat, 11 Dec 2021 19:02:31 GMT

Hi to all,

switching back and forth between javascript and flex (actually AS), I found that the most useful and fantastic pattern that is raising in the JS world are Promises.
Promises are a programming construct that have been around since 1976, and even Dojo have a promise package:

http://dojotoolkit.org/reference-guide/1.9/dojo/promise.html

In short, a promise represents a value that is not yet known and a deferred represents work that is not yet finished.

The beauty is that you can concatenate your functions like this:

queryForGeometry()
  .then(fillGeometry)
  .then(queryForKeygis)
  .then(fillKeygis)
  .then(completeUpdate)
  .done();

After some research I've found this library: https://github.com/CodeCatalyst/promise-as3

And finally I can say goodbye to nested callbacks! And with only one line of code you can adapt your query and identify to use promise!

// Somewhere in your code, at the load of the Application
Promise.registerAdapter( AsyncTokenAdapter.adapt );

var task:QueryTask = new QueryTask(Endpoint.QUERY_LAYER_FOR_BUILDING);
var query:Query = new Query();
query.where = "1=1";
query.outFields = ["*"];
// query initialisation ...
Promise.when(task.execute(query)).then(doSomethingWithQueryResult);

function doSomethingWithQueryResult(featureSet:FeatureSet):void {
 ...
}

With only one query is really simple and maybe not so revolutionary, but when you have more query that depends on other query this pattern simplify a lot my code and it's much simple to read.
The functions are all on the same level, executed in sequence and no more nested!

function queryForGeometry():Promise {
  ...
}
    
function fillGeometry(featureSet:FeatureSet, token:Object = null):Graphic {
  ...
}
    
function queryForKeygis(feature:Graphic):Promise {
  ...
}
   
function fillKeygis(featureSet:FeatureSet, token:Object = null):Object {
  ...
}

You can even do some thing like this, call a webservice, receive the result, the execute a query with some data...easy!

public class Http {
  public static function get(uri:String):Promise {
    var service:HTTPService = new HTTPService();
    service.url = encodeURI(uri);
    var header:Object = new Object();
    header["Accept"] = "application/json; charset=utf-8";
    service.headers = header;
    return Promise.when(service.send());
  }
}

// In another class, some function to query

Http.get("http://.../streets/1").then(parseJson).then(queryGISLayerWithId).done();

Happy Coding!

Re: Flex developers, embrace Promise!

DasaPaddock — Thu, 27 Mar 2014 16:57:39 GMT

Thanks for the great tip!

topic Flex developers, embrace Promise! in ArcGIS API for Flex Questions

Flex developers, embrace Promise!

Re: Flex developers, embrace Promise!