How to get data from a webapi, parse it and display it on the Windows Phone 7

Question

I made a post erlier this day about getting data from an webapi on the windows phone 7 but I think I overcomplicated things and were too unclear about what I wanted to do.

Now the thing I am trying to do is having a method going out and fetch some data in xml from a webapi and the returns it parsed to a class.

For example:

    public List<Alliance> getAllianceList()
    {
        const string serviceUrl = "/eve/AllianceList.xml.aspx";

        string xml = getXML(serviceUrl);

        //Some parsing logic and then returns it.
    }

In the getXML I am trying to get the data using the WebClient or the HttpWebRequest(Does not know wich one is the best) and then returns it. But the problem in my scenario is that it is async and I don't have much knowledge about async.

This is how I have made it so far:

    private string _xml = "";
    public string getXML(string serviceUrl)
    {
        var webClient = new WebClient();
        webClient.DownloadStringCompleted += webClient_DownloadStringCompleted;
        webClient.DownloadStringAsync(new Uri(ApiUrl + serviceUrl));
    }

    void webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
    {
        if (e.Error == null)
        {
            _xml = e.Result;
        }
    }

Now the thing I don't understand is how to go on with the parsing in getAllianceList if the request is async. Should I make the whole "chain" from and including getAllianceList async? And if so how?

Is this a god way to do the things i'm asking for? http://stackoverflow.com/questions/3846186/async-calls-in-wp7 Should I do the whole "chain" async and using INotifyPropertyChanged? — Beijer, Dec 30 '10 at 20:21

score 3 · Answer 1 · answered Dec 30 '10 at 19:01

3

Firstly I'd recommend HttpWebRequest to avoid blocking the UI Thread. Explained further in my post here.

WebClient, HttpWebRequest and the UI Thread on Windows Phone 7

You can then pass the stream you get in the callback to XDocument.Load() to parse the XML and do your business with it.

There's a basic sample of parsing this XML and databinding in my post below that begins with XDocument.Load() (in this case using a XAP file, but the principle is the same).

binding a Linq datasource to a listbox

answered Dec 30 '10 at 19:01

Mick N

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Thanks, The main problem i have now is how i can get the data from the callback when it is done and continuing the parsing in the getAllainceList method without locking up the UI thred. The list of alliances is very big as you can see. http://api.eveonline.com/eve/AllianceList.xml.aspx – Beijer Dec 30 '10 at 19:11
This becomes then a question of how your code is organised. Sure you can invoke your parsing logic from the callback, but some will prefer to have a seperation of concerns and keep that logic out of the call back. I would suggest a publish and subscribe mechanism using events to accomplish that. So your class that does the download for you can publish an event. Your class that consumes that content can subscribe to it and in the corresponding event handler perform the parsing. It's a little more fiddly, but that is the nature of async. At least we get benefits from async too. – Mick N Dec 30 '10 at 22:09
Ok, thank you. I will try that and learn a bit more about async before i start. – Beijer Dec 31 '10 at 07:27

score 0 · Answer 2 · answered Dec 31 '10 at 08:28

Is this a valid way to do it?

    private const string apiUrl = "http://api.eveonline.com";
    public void UpdateAllianceList()
    {
        const string serviceUrl = "/eve/AllianceList.xml.aspx";

        var wc = new WebClient();
        wc.DownloadStringCompleted += (s, args) =>
                                          {
                                              var worker = new Thread(ParseXmlThread);;
                                              worker.Start(args.Result);
                                          };

        wc.DownloadStringAsync(new Uri(apiUrl + serviceUrl));
    }

    private void ParseXmlThread(object xml)
    {       
        // PARSING & ADDING TO THE VIEWMODEL.
    }

Use `BackgroundWorker` instead of `Thread` directly. See http://stackoverflow.com/questions/7155942/threading-wp7-in-comparison-with-android/7192406#7192406 Parse your xml in `DoWork` and add the objects in `RunWorkerCompleted` (adding to ViewModel must be done in UI thread) — Rico Suter, Sep 25 '11 at 12:25

How to get data from a webapi, parse it and display it on the Windows Phone 7

2 Answers2