Can't read data from WCF data service using titanium - titanium

Question

I created a WCF data service which return JSON format
public static void InitializeService(DataServiceConfiguration config)
{
// TODO: set rules to indicate which entity sets and service operations are visible, updatable, etc.
// Examples:
config.SetEntitySetAccessRule("", EntitySetRights.AllRead);
config.SetServiceOperationAccessRule("", ServiceOperationRights.All);
config.DataServiceBehavior.MaxProtocolVersion = DataServiceProtocolVersion.V2;
}
i used titanium to connect to web service to get data
var label= Titanium.UI.createLabel({
top:300
});
var data = [];
// Connecting to WCF data service
var xhr = Titanium.Network.createHTTPClient();
var theURL = 'http://localhost:4338/DataService.svc/Orders?$format=json';
var json;
xhr.onload = function (){
var json = JSON.parse(this.responseText);
};
for (var i = 0 ; i < json.length; i++)
{
data.push(json[i]);
}
label.text = data[0].OrderID;
xhr.open('Get',theURL);
what is wrong

Answer 1

First of all you have to be aware that HTTP requests are asynchchronous, which means although it will take some time to fetch the response (depending on the internet connection, server speed, data size etc.), the succeeding code is executed. If the request was synchronous, it would block the app and any user interaction while it loads. That is why the client provides callbacks that are fired on certain state changes.
Your code
var data = [];
// Connecting to WCF data service
var xhr = Titanium.Network.createHTTPClient();
// Just guessing, but is the $ necessary?
var theURL = 'http://localhost:4338/DataService.svc/Orders?$format=json';
// You are defining json here 'globally'
var json;
xhr.onload = function (){
// You are defining the json variable within the scope of
// the onload function, so it can't be accessed from outside
// the function. Moreover, you are overwriting json of the global scope
// within this function
var json = JSON.parse(this.responseText);
};
// At this point, json is undefined
// Moreover, this code is executed before xhr.onload fires
for (var i = 0 ; i < json.length; i++)
{
data.push(json[i]);
}
label.text = data[0].OrderID;
// Method should be GET not Get
xhr.open('Get',theURL);
How it should work
var data = [];
var theURL = 'http://localhost:4338/DataService.svc/Orders?format=json';
var xhr = Titanium.Network.createHTTPClient();
xhr.onload = function (){
// Assuming that you have a valid json response
var json = JSON.parse(this.responseText);
for (var i=0; i < json.length; i++) {
data.push(json[i]);
}
// For testing, otherwise make sure it won't break if your response is empty
label.text = data[0].OrderID;
};
xhr.open('GET', theURL);