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Home Forums Silverlight Programming Programming with JavaScript How to use the XMLHttpRequest() "AJAX method" in SilverLight
9 replies. Latest Post by MarkMonster on June 29, 2009.
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anilk_go...
Member
2 points
12 Posts
06-24-2009 3:02 AM |
Hi,
I am new in SilverLight. I have created an AJAX application to check the status code (404, 200 etc...). Now I want to do the same functionality with the silverlight application. Can please anyone tell me how can I do this in the SilverLight application. For reference the AJAX applcation is given below:
html><head><title>Updating status page using Ajax</title><script type=text/javascript language=javascript><!-- Hide Javascript on old browsers
function aboutlang() {
/* Get back the server status */
var xmlhttp=false;
try { xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); } catch (e) { try { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); } catch (E) { xmlhttp = false; } }
if (!xmlhttp) { try { xmlhttp = new XMLHttpRequest(); } catch (e) { xmlhttp=false; } }
xmlhttp.open('GET',"http://localhost/ajax/time.asp",false); xmlhttp.send(null);
if (xmlhttp.readyState==4) { if (xmlhttp.status==200){ alert("Success - It is a 200!"); } else if (xmlhttp.status==401){ alert("Credentials required!"); } else if (xmlhttp.status==403){ alert("Access denied !!!"); } else if (xmlhttp.status==302){ alert("It's a redirect !!!"); } else if (xmlhttp.status==404){ alert("It's a 404"); } else{ alert("Status is "+xmlhttp.status); } }
return false;}</script></head><body onload="aboutlang()"></body></html>
MarkMonster
Contributor
5124 points
1,038 Posts
06-24-2009 4:14 AM |
In Silverlight you're able to make use of HttpWebRequest. Please take a look at the example on this page: http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest(VS.95).aspx
06-24-2009 6:21 AM |
Please tell me RequestState class is present in which library. Is it a custom class?
06-24-2009 7:18 AM |
Yes the RequestState mentioned in the example is a custom class. And looks probably something like this:
class RequestState { public HttpWebRequest request; // holds the request public HttpWebResponse response; // holds the response }
06-25-2009 6:59 AM |
Thanks a lot. Here I succesfully writing a code to get all the information from the requested header. I successfully get all the information into string variable but when I try to copy the string to textbox (here i use the messagebox in following code) it gives the exception ("Invalid cross thread error"). please can u tell me here what can I do. the code sniped in given below:
{
req.BeginGetResponse(getResponse, req);
}
ResponseHeaders +=
client.DownloadStringAsync(uri);
outputBlock.Text += e.Error.ToString();
06-25-2009 8:46 AM |
This basically because the response coming to you on a different thread. To manipulate UI elements, like MessageBox, you need to be on the UI-Thread. For detailed information you can take a look at my article on getting back to the UI Thread.
if(Dispatcher.CheckAccess()) { Dispatcher.BeginInvoke(()=>MessageBox.Show(s)); }
06-26-2009 12:13 AM |
Thanks a lot. Now I successfully getting the values in the messagebox.
Now, i am facing a new problem that is, when the html page that I have request is exists (HttpStatusCode = "OK") then everything is working fine. But when the page is not exists then I got an runtime error (Exception) in the code. Also, please tell me how I access the another URLs not in the same domain.
HttpWebResponse
The code sniped is given below:
private void Button_click(object sender, RoutedEventArgs e){ HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(new Uri("http://localhost:53347/ab.htm")); req.BeginGetResponse(getResponse, req);}
void getResponse(IAsyncResult ar){
HttpWebRequest req = (HttpWebRequest)ar.AsyncState; HttpWebResponse res = (HttpWebResponse)req.EndGetResponse(ar);
if (res.StatusCode == HttpStatusCode.OK) { string ResponseHeaders = "ContentType : " + res.ContentType.ToString() + "\n"; ResponseHeaders += "ContentLength : " + res.ContentLength.ToString() + "\n"; this.Dispatcher.BeginInvoke(delegate() { myTextBox.Text = ResponseHeaders; }); }}
06-26-2009 2:12 AM |
First of all, you will need to add proper handling of exceptions. So please add Try/Catch blocks.
To access URLs on a different domain you will have to take into consideration Cross Domain problems.
If the other domain has a file like "clientaccesspolicy.xml" or "crossdomain.xml" in the root of it's domain it might be possible, if it doesn't have this kind of CrossDomain Access file and you're not able to put such a file on that domain, you will have to take a different approach.
This approach could be to communicate with your own trusted server which can in that case also serve as a proxy between you and the domain that cannot be crossed using Silverlight.
06-29-2009 12:52 AM |
Thanks a lot !!!
Now, everything is working fine. But here with "WebRequest" or "WebClient" object I am able to identify only the "HTTPStatusCode - 404 or 200". Please tell me how I identy the "HTTPStatusCode - 401". If you have any sample code sniped than please share it.
06-29-2009 2:51 AM |
Sory, I haven't got any more details on those statuscodes. Does it not work the same like 404 and 200?
How to use the XMLHttpRequest() "AJAX method" in SilverLight