I have a dynamic page with a .JSON file, and I'm using my C# program to access it every x number of seconds, to determine if something has been changed or not. Everything works flawlessly as long as I have Internet connection, if for whatever reason I lose it, then my program crashes as the ex.Response is a null. I was wondering if there's a better way of handling the following code:
void Function(){
while(true){
jList = new System.Web.Script.Serialization.JavaScriptSerializer().Deserialize<jsonList>(GET(jsonUrl));
//SOME THINGS I DO with the data above here
Thread.Sleep(5000);
}}
string GET(string url)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
try
{
WebResponse response = request.GetResponse();
using (Stream responseStream = response.GetResponseStream())
{
StreamReader reader = new StreamReader(responseStream, Encoding.UTF8);
return reader.ReadToEnd();
}
}
catch (WebException ex)
{
WebResponse errorResponse = ex.Response;
if (ex.Response != null) {
using (Stream responseStream = errorResponse.GetResponseStream())
{
StreamReader reader = new StreamReader(responseStream, Encoding.GetEncoding("utf-8"));
String errorText = reader.ReadToEnd();
// log errorText
}
}
throw;
}
}
Perhaps I should ping it first, and see if I get a reply, and only then Perform the WebRequest function?
EDIT:
After adding this
public bool getResponse(string URL)
{
try
{
WebClient wc = new WebClient();
string HTMLSource = wc.DownloadString(URL);
return true;
}
catch (Exception)
{
return false;
}
}
And use it as
void Function(){
while(true){
if (!getResponse(jsonUrl))
{
return;
}
jList = new System.Web.Script.Serialization.JavaScriptSerializer().Deserialize<jsonList>(GET(jsonUrl));
//SOME THINGS I DO with the data above here
Thread.Sleep(5000);
}}
My C# application waits a bit, and then exits normally. Why?
The program '[10476] Kiosk2.vshost.exe' has exited with code 0 (0x0).
Alright, well this seems to work fine for me.
public void Update() //CALLED IT void FUNCTION earlier
{
while (true)
{
while (getResponse(jsonUrl))
{
jList = new System.Web.Script.Serialization.JavaScriptSerializer().Deserialize<jsonList>(GET(jsonUrl));
//I DO SOME STUFF HERE
//INTERESTING STUFF
Thread.Sleep(5000);
}
}
}
And seconds function:
public bool getResponse(string URL)
{
try
{
WebClient wc = new WebClient();
string HTMLSource = wc.DownloadString(URL);
return true;
}
catch (Exception)
{
return false;
}
}
Related
I'm trying use HttpWebRequest, and my BeginGetRequestStream works but it never enters the BeginGetResponse function and i have no idea why.. i've searched for a couple of hours and have not found a solution that works
public void Initialize(IScheduler scheduler)
{
if(_isCloud)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(_cloudMappingServer + "/Mapping/GetAllCentralPoints");
request.ContentType = "application/x-www-form-urlencoded";
request.Method = "POST";
request.BeginGetRequestStream(new AsyncCallback(ReleaseReadCallback), request);
// Instruct the thread to wait until we resume it
_waitHandle.WaitOne();
_waitHandle.Dispose();
}
}
private void ReleaseReadCallback(IAsyncResult asynchronousResult)
{
try
{
HttpWebRequest httpRequest = (HttpWebRequest)asynchronousResult.AsyncState;
using (Stream postStream = httpRequest.EndGetRequestStream(asynchronousResult))
{
using (MemoryStream memStream = new MemoryStream())
{
string queryString = string.Empty;
byte[] bytes = System.Text.Encoding.UTF8.GetBytes(queryString);
memStream.Write(bytes, 0, bytes.Length);
memStream.Position = 0;
byte[] tempBuffer = new byte[memStream.Length];
memStream.Read(tempBuffer, 0, tempBuffer.Length);
postStream.Write(tempBuffer, 0, tempBuffer.Length);
}
}
httpRequest.BeginGetResponse(new AsyncCallback(ReleaseResponseCallback), httpRequest);
}
catch (Exception ex)
{
var test = ex;
}
}
private void ReleaseResponseCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest responseRequest = (HttpWebRequest)asynchronousResult.AsyncState;
string responseString = string.Empty;
try
{
using (HttpWebResponse resp = (HttpWebResponse)responseRequest.EndGetResponse(asynchronousResult))
{
using (StreamReader streamRead = new StreamReader(resp.GetResponseStream()))
{
responseString = streamRead.ReadToEnd();
try
{
JsonSerializerSettings settings = new JsonSerializerSettings();
List<CentralPointViewModel> _allCentralPointViewModel = JsonConvert.DeserializeObject<List<CentralPointViewModel>>(responseString, settings);
}
catch (JsonReaderException)
{
responseString = responseString.Replace('\"'.ToString(), string.Empty);
string[] responseArray = responseString.Split(';');
}
catch (JsonSerializationException)
{
responseString = responseString.Replace('\"'.ToString(), string.Empty);
}
}
}
}
catch (Exception ex)
{
}
}
It never enters the ReleaseResponseCallback function! I am able to make my server call but the response never reaches me or I am not properly receiving it.. Any help is appreciated
Good night, I'm trying to call the UI thread, to update a proprety actualy, inside HttpWebRequest.BeginGetResponse method by using CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync method. But it does not work, I do not know how it works actually. There is my code:
private void DebutReponse(IAsyncResult resultatAsynchrone)
{
HttpWebRequest requete = (HttpWebRequest)resultatAsynchrone.AsyncState;
Stream postStream = requete.EndGetRequestStream(resultatAsynchrone);
string donneesAEnvoyer = "username=" + Name + "&password=" + Password + "&email=" + Email;
string lol = donneesAEnvoyer;
byte[] tableau = Encoding.UTF8.GetBytes(donneesAEnvoyer);
postStream.Write(tableau, 0, donneesAEnvoyer.Length);
postStream.Close();
requete.BeginGetResponse(FinReponse, requete);
}
private void FinReponse(IAsyncResult resultatAsynchrone)
{
HttpWebResponse aResp = null;
try
{
HttpWebRequest requete = (HttpWebRequest)resultatAsynchrone.AsyncState;
WebResponse webResponse = requete.EndGetResponse(resultatAsynchrone);
Stream stream = webResponse.GetResponseStream();
StreamReader streamReader = new StreamReader(stream);
string reponse = streamReader.ReadToEnd();
stream.Close();
streamReader.Close();
webResponse.Close();
//ErrorGridHeight = new GridLength(0.3, GridUnitType.Star);
ErrorMsg = msgSucceed;
}
catch (WebException e)
{
if (e.Response != null)
{
aResp = e.Response as HttpWebResponse;
}
}
if (aResp != null)
await errorFunc();
}
private async Task errorFunc()
{
await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => ErrorMsg = msgFailed);
}
I have an error telling me that I can only use the await operator inside an async method who return a Task. I have no idea how it works.
EDIT:
Ok so I changed my code a little bit to avoid the problem of this function:
requete.BeginGetResponse(FinReponse, requete);
because she want a function with a specific prototype so I did this:
private async Task lol(IAsyncResult resultatAsynchrone)
{
HttpWebResponse aResp = null;
try
{
HttpWebRequest requete = (HttpWebRequest)resultatAsynchrone.AsyncState;
WebResponse webResponse = requete.EndGetResponse(resultatAsynchrone);
Stream stream = webResponse.GetResponseStream();
StreamReader streamReader = new StreamReader(stream);
string reponse = streamReader.ReadToEnd();
stream.Close();
streamReader.Close();
webResponse.Close();
//ErrorGridHeight = new GridLength(0.3, GridUnitType.Star);
ErrorMsg = msgSucceed;
}
catch (WebException e)
{
if (e.Response != null)
{
aResp = e.Response as HttpWebResponse;
}
}
if (aResp != null)
await errorFunc();
}
private void FinReponse(IAsyncResult resultatAsynchrone)
{
Task.Run(() => lol(resultatAsynchrone));
}
private async Task errorFunc()
{
await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => ErrorMsg = msgFailed);
}
The only problem is that it does not change the proprety, it does not go into the set of my proprety. And I have an exeption which is:
System.NotImplementedExeption
Thank you for the help.
Try to change your errorFunc() to this.
private void errorFunc()
{
CoreApplication.MainView.CoreWindow.Dispatcher.BeginInvoke(() =>
{
ErrorMsg = msgFailed;
});
}
I also found another place, where you're trying to change ErrorMsg witouth calling the UI thread. It's the line with code ErrorMsg = msgSucceed;. I suggest to use the same way, so replace the line with this:
CoreApplication.MainView.CoreWindow.Dispatcher.BeginInvoke(() =>
{
ErrorMsg = msgSucceed;
});
You have to do FinReponse method async to be able to use await operator into it:
private async void FinReponse(IAsyncResult resultatAsynchrone)
So I found the answer to access the UI, I have to use:
Deployment.Current.Dispatcher.BeginInvoke(()=>mym());
and it works perfectly.
Thanks for everythings.
So I'm using the HttpWebRequest API in the System.Net assembly but because C# has no checked exceptions, I'm not sure where to put my try-catch blocks to properly handle inevitable exceptions caused by common things like a network error. You know, in Java we would call these plain old checked IOExceptions.
This is what I have so far. Are my try-catch blocks properly set up to handle network errors? Am I wrapping the right method calls? Looking at the documentation, I think they are right, but I need a second pair of eyes.
HttpWebRequest request = WebRequest.CreateHttp(url);
request.Method = "POST";
request.BeginGetRequestStream(getRequestResult =>
{
HttpWebRequest getRequestRequest = (HttpWebRequest) getRequestResult.AsyncState;
try
{
Stream requestStream = getRequestRequest.EndGetRequestStream(getRequestResult);
requestStream.Write(parametersData, 0, parametersData.Length);
requestStream.Dispose();
getRequestRequest.BeginGetResponse(getResponseResult =>
{
HttpWebRequest getResponseRequest = (HttpWebRequest)getResponseResult.AsyncState;
try
{
WebResponse response = getResponseRequest.EndGetResponse(getRequestResult);
Stream responseStream = response.GetResponseStream();
StreamReader reader = new StreamReader(responseStream);
string jsonString = reader.ReadToEnd();
reader.Dispose();
JObject jsonObject = JObject.Parse(jsonString);
onResult(StatusCode.Ok, jsonObject);
}
catch (WebException)
{
onResult(StatusCode.NetworkError);
}
}, getRequestRequest);
}
catch (IOException)
{
onResult(StatusCode.NetworkError);
}
}, request);
First off, unless there's some reason that you need to use HttpWebRequest, then you're better off using WebClient.UploadString instead, or any of WebClient's other UploadXXX overloads for uploading name/value pairs, files, binary data, etc. This will be much easier for you, and easier to troubleshoot and debug. Also, another problem is that you're treating exceptions during JSON parsing or during your onResult handler error as network errors.
Below are three examples of using WebClient that you might want to try: a synchronous version, an "old-style" async version, and a "new-style" async version that uses async/await. All three versions also try to fix the exception handling issue that I noted above. If you don't need async support, then the first version will be easiest.
static void PostSync (string url, string parametersData)
{
using (WebClient wc = new WebClient())
{
wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded"; // or "application/json" or ...
try
{
string htmlResult = wc.UploadString(url, parametersData); // or UploadValues, UploadFile, ...
JObject jsonObject = null;
try
{
jsonObject = JObject.Parse(htmlResult);
}
catch (JsonException ex)
{
onResult(StatusCode.JsonError);
}
onResult(StatusCode.Ok, jsonObject);
}
catch (System.Net.WebException ex)
{
onResult(StatusCode.NetworkError);
}
}
}
static void PostAsync(string url, string parametersData)
{
using (WebClient wc = new WebClient())
{
wc.UploadStringCompleted += (Object sender, UploadStringCompletedEventArgs e) =>
{
if (e.Error != null)
onResult(StatusCode.NetworkError);
JObject jsonObject = null;
try
{
jsonObject = JObject.Parse(e.Result);
}
catch (JsonException ex)
{
onResult(StatusCode.JsonError);
}
onResult(StatusCode.Ok, jsonObject);
};
try
{
wc.UploadStringAsync(new Uri(url, UriKind.Absolute), parametersData);
}
catch (System.Net.WebException ex)
{
onResult(StatusCode.NetworkError);
}
}
}
static async void PostTaskAsync(string url, string parametersData)
{
using (WebClient wc = new WebClient())
{
wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded"; // or "application/json" or ...
try
{
string htmlResult = await wc.UploadStringTaskAsync(url, parametersData); // or UploadValues, UploadFile, ...
JObject jsonObject = null;
try
{
jsonObject = JObject.Parse(htmlResult);
}
catch (JsonException ex)
{
onResult(StatusCode.JsonError);
}
onResult(StatusCode.Ok, jsonObject);
}
catch (System.Net.WebException ex)
{
onResult(StatusCode.NetworkError);
}
}
}
private void RespCallback(IAsyncResult asynchronousResult)
{
try
{
WebRequest myWebRequest1 = (WebRequest)asynchronousResult.AsyncState;
// End the Asynchronous response.
WebResponse webResponse = myWebRequest1.EndGetResponse(asynchronousResult);
}
catch (Exception)
{
// TODO:Log the error
}
}
Now having the webResponse object, what is the easiest way to read its contents?
I would simply use the async methods on WebClient - much easier to work with:
WebClient client = new WebClient();
client.DownloadStringCompleted += (sender,args) => {
if(!args.Cancelled && args.Error == null) {
string result = args.Result; // do something fun...
}
};
client.DownloadStringAsync(new Uri("http://foo.com/bar"));
But to answer the question; assuming it is text, something like (noting you may need to specify the encoding):
using (var reader = new StreamReader(response.GetResponseStream()))
{
string result = reader.ReadToEnd(); // do something fun...
}
Here is one way to do it if the response is coming in from XML.
HttpWebRequest myReq = (HttpWebRequest)WebRequest.Create("https://www.yoururl.com");
WebResponse response = myReq.GetResponse();
Stream responseStream = response.GetResponseStream();
XmlTextReader reader = new XmlTextReader(responseStream);
while (reader.Read())
{
if (reader.NodeType == XmlNodeType.Text)
{
Console.WriteLine("{0}", reader.Value.Trim());
}
Console.ReadLine();
}
internal string Get(string uri)
{
using (WebResponse wr = WebRequest.Create(uri).GetResponse())
{
using (StreamReader sr = new StreamReader(wr.GetResponseStream()))
{
return sr.ReadToEnd();
}
}
}
I would like to know which approach among the two is a better implementation ?
I need to create a web request which can range between 200ms to 5 seconds. I need the html response to proceed - so need to block on the main thread.
First Approach
string GetResponse()
{
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
IAsyncResult result = request.BeginGetResponse(null, null);
using (HttpWebResponse httpResponse = (HttpWebResponse)request.EndGetResponse(result))
{
using (Stream dataStream = httpResponse.GetResponseStream())
{
StreamReader reader = new StreamReader(dataStream);
response = reader.ReadToEnd();
}
}
Second Approach
string response = string.Empty;
AutoResetEvent waitHandle = null;
void GetResponse(string url)
{
waitHandle = new AutoResetEvent(false);
try
{
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
IAsyncResult asyncResult = request.BeginGetResponse(Callback, request);
waitHandle.WaitOne();
}
catch { }
finally
{
waitHandle.Close();
}
}
void Callback(IAsyncResult asyncResult)
{
HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
try
{
using (HttpWebResponse httpResponse = (HttpWebResponse)request.EndGetResponse(asyncResult))
{
if (httpResponse.StatusCode == HttpStatusCode.OK)
{
using (Stream dataStream = httpResponse.GetResponseStream())
{
StreamReader reader = new StreamReader(dataStream);
response = reader.ReadToEnd();
}
}
}
}
catch { }
finally
{
waitHandle.Set();
}
}
Why not execute the web request on the main thread? If you want the main thread to block, this is by far the easiest way to accomplish this.