So in my app I have a button that talks to a lib that downloads some data from the internet and filters it. When the app is doing this the screen freezes and it looks to the user like the app crashed. But this is not the case because its downloading data.
Here is my code:
GetDetailsBtn.TouchUpInside += (sender, e) => {
var defaults = NSUserDefaults.StandardUserDefaults;
if (RefNr.Text != string.Empty && RefNr.Text != null) {
FilteredDataRef = _FetchingData.getTrackTraceData (defaults.StringForKey ("SecurityToken"), RefNr.Text);
if (FilteredDataRef == null) {
UIAlertView InvalidAlert = new UIAlertView ("Reference number invalid", "The reference number that you have entered is not linked to the current security code. You can change your security code in the settings.", null, "OK", null);
InvalidAlert.Show ();
} else {
FilteredDataReceived = _FetchingData.FilteringOnReceived (FilteredDataRef);
FilteredDataPlanned = _FetchingData.FilteringOnPlanned (FilteredDataRef);
FilteredDataLoadingETA = _FetchingData.FilteringOnLoadingETA (FilteredDataRef);
FilteredDataLoadingFinal = _FetchingData.FilteringOnLoadingFinal (FilteredDataRef);
FilteredDataUnloadingETA = _FetchingData.FilteringOnUnloadingETA (FilteredDataRef);
FilteredDataUnloadingFinal = _FetchingData.FilteringOnUnloadingFinal (FilteredDataRef);
this.PerformSegue (MoveToTrackTraceDetailsSegue, this);
//foreach (string s in FilteredDataPlanned)
// Console.WriteLine (s);
}
} else {
UIAlertView InvalidAlert = new UIAlertView ("Reference number cannot be empty", "You did not provide a reference number. We need your reference number to trace identify the shipment you would like to trace.", null, "OK", null);
InvalidAlert.Show ();
}
};
Downloading of the data:
public IEnumerable<string> getTrackTraceData (string securityCode, string referenceNumber)
{
WebRequest request = WebRequest.Create ("http://plex.janssen1877.com/app/life/" + securityCode);
HttpWebResponse response = (HttpWebResponse)request.GetResponse ();
Stream dataStream = response.GetResponseStream ();
StreamReader reader = new StreamReader (dataStream);
string FetchedData = reader.ReadToEnd ();
reader.Close ();
dataStream.Close ();
response.Close ();
var FetchingDataItems = FetchedData.Split (new char[] { '\n' });
if (FetchingDataItems != null) {
var filteredResult = FetchingDataItems.Where (x => x.Contains (referenceNumber));
return filteredResult;
} else {
return null;
}
}
Now I want to use a component called BTProgressHUD. This is just a fancy spinner. I thought that if I would put BTProgressHUD.show(); to the top of the button action and BTProgressHUD.Dismiss(); to the button it would show when the loading starts and dismiss when its done loading.
This is not the case. It shows very quickly in the new view controller and dismisses again within a second. What am I doing wrong?
Edit for exemple:
public IEnumerable<string> getTrackTraceData (string securityCode, string referenceNumber)
{
string url = string.Format ("http://plex.janssen1877.com/app/life/" + securityCode);
HttpWebRequest HttpRequest = (HttpWebRequest)WebRequest.Create (url);
string FetchedData = new StreamReader (HttpRequest.GetResponse ().GetResponseStream ()).ReadToEnd ();
var FetchingDataItems = FetchedData.Split (new char[] { '\n' });
if (FetchingDataItems != null) {
var filteredResult = FetchingDataItems.Where (x => x.Contains (referenceNumber));
return filteredResult;
} else {
return null;
}
}
Florian,
According to .NET documentation and HttpWebRequest GetResponse. How to wait for that response? you need to perform the download (and maybe the parsing) in a async fashion.
The behavior of your actual application is correct. When you perform a sync request in the main thread you freeze the application and hence the UI elements are not updated. The main thread processes execution in a serial fashion.
To avoid this you have two different solutions. On the one hand, you need to move to an async request. On the other hand, you can create a background thread (a different path of execution) with a sync request. I prefer the former. So, for example, after starting the async request, show the indicator. When you have finished (in the callback), dismiss the indicator and perform the segue.
For example, you can follow the following discussion on how to achieve this: How to use HttpWebRequest (.NET) asynchronously?.
To understand how the main thread (and the run loop) works, I suggest to read about The pogo stick of NSRunLoop.
Hope that helps.
Edit
You should use a pattern like the following (source How to use HttpWebRequest (.NET) asynchronously?):
HttpWebRequest webRequest;
void StartWebRequest()
{
webRequest.BeginGetResponse(new AsyncCallback(FinishWebRequest), null);
}
void FinishWebRequest(IAsyncResult result)
{
webRequest.EndGetResponse(result);
}
It sounds like you're attempting to do all this in the same thread as your UI, which is why your app freezes and waits for processing to finish without showing anything. I would perform this download operation in a backgroundworker of some sort. Then I am not sure in Mono but access the main thread before and after and show and dismiss your loading component.
Related
Sorry if the title is not clear or correct, dont know what title should i put. Please correct if wrong.
I have this code to download images from IP camera and it can download the images.The problem is how can i do the images downloading process at the same time for all cameras if i have two or more cameras?
private void GetImage()
{
string IP1 = "example.IPcam1.com:81/snapshot.cgi;
string IP2 = "example.IPcam2.com:81/snapshot.cgi;
.
.
.
string IPn = "example.IPcamn.com:81/snapshot.cgi";
for (int i = 0; i < 10; i++)
{
string ImagePath = Server.MapPath("~\\Videos\\liveRecording2\\") + string.Format("{0}", i, i + 1) + ".jpeg";
string sourceURL = ip;
WebRequest req = (WebRequest)WebRequest.Create(sourceURL);
req.Credentials = new NetworkCredential("user", "password");
WebResponse resp = req.GetResponse();
Stream stream = resp.GetResponseStream();
Bitmap bmp = (Bitmap)Bitmap.FromStream(stream);
bmp.Save(ImagePath);
}
}
You should not run long-running code like that from an ASP.NET application. They are meant to simply respond to requests.
You should place this code in a service (Windows Services are easy), and control the service through a WCF service running inside of it.
You're also going to get into trouble because you don't have your WebResponse and Stream in using blocks.
There are several methods that will depend on how you want to report feedback to the user. It all comes down to multi-threading.
Here is one example, using the ThreadPool. Note that this is missing a bunch of error checking throughout... It is here as an example of how to use the ThreadPool, not as a robust application:
private Dictionary<String, String> _cameras = new Dictionary<String, String> {
{ "http://example.IPcam1.com:81/snapshot.cgi", "/some/path/for/image1.jpg" },
{ "http://example.IPcam2.com:81/snapshot.cgi", "/some/other/path/image2.jpg" },
};
public void DoImageDownload() {
int finished = 0;
foreach (KeyValuePair<String, String> pair in _cameras) {
ThreadPool.QueueUserWorkItem(delegate {
BeginDownload(pair.Key, pair.Value);
finished++;
});
}
while (finished < _cameras.Count) {
Thread.Sleep(1000); // sleep 1 second
}
}
private void BeginDownload(String src, String dest) {
WebRequest req = (WebRequest) WebRequest.Create(src);
req.Credentials = new NetworkCredential("username", "password");
WebResponse resp = req.GetResponse();
Stream input = resp.GetResponseStream();
using (Stream output = File.Create(dest)) {
input.CopyTo(output);
}
}
This example simply takes the work you are doing in the for loop and off-loads it to the thread pool for processing. The DoImageDownload method will return very quickly, as it is not doing much actual work.
Depending on your use case, you may need a mechanism to wait for the images to finish downloading from the caller of DoImageDownload. A common approach would be the use of event callbacks at the end of BeginDownload to notify when the download is complete. I have put a simple while loop here that will wait until the images finish... Of course, this needs error checking in case images are missing or the delegate never returns.
Be sure to add your error checking throughout... Hopefully this gives you a place to start.
I have a page which is fetching data from a webservice using async call.
If i get the response from webservice control goes to catch where a message box is pooped.
The code is given below:
string uri = "http://free.worldweatheronline.com/feed/weather.ashx?key=b7d3b5ed25080109113008&q=Mumbai&num_of_days=5";
UriBuilder fullUri = new UriBuilder("http://free.worldweatheronline.com/feed/weather.ashx");
fullUri.Query = "key=b7d3b5ed25080109113008&q=Mumbai&num_of_days=5";
HttpWebRequest forecastRequest = (HttpWebRequest)WebRequest.Create(fullUri.Uri);
// set up the state object for the async request
ForecastUpdateState forecastState = new ForecastUpdateState();
forecastState.AsyncRequest = forecastRequest;
// start the asynchronous request
forecastRequest.BeginGetResponse(new AsyncCallback(HandleForecastResponse), forecastState);
This part is response
private void HandleForecastResponse(IAsyncResult asyncResult)
{
try
{
// get the state information
ForecastUpdateState forecastState = (ForecastUpdateState)asyncResult.AsyncState;
HttpWebRequest forecastRequest = (HttpWebRequest)forecastState.AsyncRequest;
// end the async request
forecastState.AsyncResponse = (HttpWebResponse)forecastRequest.EndGetResponse(asyncResult);
Stream streamResult;
string newCityName = "";
//int newHeight = 0;
// get the stream containing the response from the async call
streamResult = forecastState.AsyncResponse.GetResponseStream();
// load the XML
XElement xmlWeather = XElement.Load(streamResult);
}
catch (Exception ex)
{
MessageBox.Show("Connection Error");
}
}
Problem :
when the page is loaded it starts fetching data from webservice(consider the case when the web service is not responding and control goes to catch part).
In the mean time if we press the back button or navigate the page the message box popps on the new page.
How could i stop that.
Thanks and Regards
Haven't tested it, but it may work:
1/ Store the value of the NavigationService.CurrentSource property somewhere it can be retrieved (the best would be in the asyncState parameter, but a property may work as well
2/ In the HandleForecastResponse, compare the old and new value of the NavigationService.CurrentSource. This way, you should be able to deduce if the active page has changed or not.
ifixed that problem by add
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(() =>
{
});
try this
private void HandleForecastResponse(IAsyncResult asyncResult)
{
try
{
// get the state information
ForecastUpdateState forecastState = (ForecastUpdateState)asyncResult.AsyncState;
HttpWebRequest forecastRequest = (HttpWebRequest)forecastState.AsyncRequest;
// end the async request
forecastState.AsyncResponse = (HttpWebResponse)forecastRequest.EndGetResponse(asyncResult);
Stream streamResult;
string newCityName = "";
//int newHeight = 0;
// get the stream containing the response from the async call
streamResult = forecastState.AsyncResponse.GetResponseStream();
// load the XML
XElement xmlWeather = XElement.Load(streamResult);
}
catch (Exception ex)
{
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(() =>
{
MessageBox.Show("Connection Error");
});
}
}
Finally solved it.
catch (Exception x)
{
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
var currentPage = ((App)Application.Current).RootFrame.Content as PhoneApplicationPage;
if ((currentPage.ToString()).Equals("MumbaiMarathon.Info.News"))
{
MessageBox.Show("Connection Error");
}
});
}
I just checked at the time of popping the message box the name of the Current UI application page. If its same as the page from which message box is initiated than it pops otherwise not.
I have a listview which I populate from a webservice query. Problem is that if the http query is slow due to network or the URL is wrong then the query freezes the UI for a bit. So my question is how do I throw this off to a side process and populate the list in the background?
Here is how I get the data and it usually sits for 30 secs or more at request.GetResponse(); I get JSON back and parse that but this function is the hold up and would like to wrap it in something. So how would I do that specifically?
public static String get(String url) {
StringBuilder sb = new StringBuilder();
// used on each read operation
byte[] buf = new byte[32768];
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "POST";
request.Timeout = 10000;
HttpWebResponse response;
try {
response = (HttpWebResponse)request.GetResponse();
} catch (WebException we) {
return "ERROR!"
}
Stream resStream = response.GetResponseStream();
... read from stream and parse
}
#### Using suggestion of Worker Thread ############
This doesn't work either.
// create new thread
new Thread(new ThreadStart(myTable) ).Start();
inside the myTable method using an anonymous delegate I thought might be the best way.
private void myTable() {
if (this.InvokeRequired) {
this.Invoke(new EventHandler(delegate(object obj, EventArgs a) {
// do work here
String url = "http://someurl....";
// Set the view to show details.
listView1.View = View.Details;
// Display check boxes.
listView1.CheckBoxes = false;
// Select the item and subitems when selection is made.
listView1.FullRowSelect = true;
listView1.Items.Clear();
listView1.Columns.Clear();
listView1.Columns.Add(Resources.MainColumn0, 20, HorizontalAlignment.Left);
listView1.Columns.Add(Resources.MainColumn1a, 250, HorizontalAlignment.Left);
listView1.Columns.Add(Resources.MainColumn2, 150, HorizontalAlignment.Left);
try {
// Call the function mentioned above to get the data from the webservices....
string users = get(urlUsers);
.............
Use a worker thread to make the query, the use Control.Invoke to update the UI or use an async call to get the data from the service. Without knowing more about exactly how you're getting the data and doing population, that's about as detailed as I can get.
EDIT
Your attempt at offloading the work to a thread is subverted by your call to Invoke, which moves everything back to the UI thread. You need to do something along these lines:
private void MyThreadProc()
{
// get the data from the web service here
this.Invoke(new EventHandler(delegate
{
// update your ListView here
}));
}
Note that the long-running part of the command is not contained within the Invoke call.
Windows mobile 5; compact framework and relative newbie to c# and threads.
I want to download large files (several meg) from my own website; being GPRS this could take a while. I want to show a progress bar, and allow an option to cancel the download.
I've got a class called FileDownload and create an instance of it; give it a url and save location then:
MyFileDownLoader.Changed += new FileDownLoader.ChangedEventHandler(InvokeProgressBar);
BGDownload = new Thread(new ThreadStart(MyFileDownLoader.DownloadFile));
BGDownload.Start();
So I create an event handler for updates to progress bar and start the thread. This works fine.
I've got a cancel button which reads:
MyFileDownLoader.Changed -= InvokeProgressBar;
MyFileDownLoader.Cancel();
BGDownload.Join();
lblPercentage.Text = CurPercentage + " Cancelled"; // CurPercentage is a string
lblPercentage.Refresh();
btnUpdate.Enabled = true;
In the FileDownload class the key parts are:
public void Cancel()
{
CancelRequest = true;
}
In method Download file:
...
success = false;
try {
//loop until no data is returned
while ((bytesRead = responseStream.Read(buffer, 0, maxRead)) > 0)
{
_totalBytesRead += bytesRead;
BytesChanged(_totalBytesRead);
fileStream.Write(buffer, 0, bytesRead);
if (CancelRequest)
break;
}
if (!CancelRequest)
success = true;
}
catch
{
success = false;
// other error handling code
}
finally
{
if (null != responseStream)
responseStream.Close();
if (null != response)
response.Close();
if (null != fileStream)
fileStream.Close();
}
// if part of the file was written and the transfer failed, delete the partial file
if (!success && File.Exists(destination))
File.Delete(destination);
The code i'm using for the download is based on http://spitzkoff.com/craig/?p=24
The problem i've got is when I cancel, the download stops immediately, however it can take up to 5 seconds or so for the join process to complete. This is evidenced by lblPercentage.Text being updated after the join.
If I then try and download again, sometimes it works and sometimes I get a nullreference exception (still trying to track that down).
I think i'm doing something wrong in my approach to cancelling the thread.
Am i ?
public void Cancel()
{
CancelRequest = true;
}
I suppose you should add thread-safe to this action.
public void Cancel()
{
lock (this)
{
CancelRequest = true;
}
}
Hope this help!
I am trying to build a c# console app that will monitor about 3000 urls (Just need to know that HEAD request returned 200, not necessarily content, etc.)
My attempt here was to build a routine the checks the web URLS, looping and creating threads each executing the routine. What's happening is if i run with <20 threads, it executes ok most of the time, but if i use >20 threads, some of the url's time out. I tried increasing the Timeout to 30 seconds, same occurs. The network I am running this on is more than capable of executing 50 HTTP HEAD requests (10MBIT connection at ISP), and both the CPU and network run very low when executing the routine.
When a timeout occurs, i test the same IP on a browser and it works fine, I tested this repeatedly and there was never a case during testing that a "timed out" url was actually timing out.
The reason i want to run >20 threads is that i want to perform this test every 5 minutes, with some of the URL's taking a full 10sec (or higher if the timeout is set higher), i want to make sure that its able to run through all URLs within 2-3 minutes.
Is there a better way to go about checking if a URL is available, or, should I be looking at the system/network for an issue.
MAIN
while (rdr.Read())
{
Thread t = new Thread(new ParameterizedThreadStart(check_web));
t.Start(rdr[0]);
}
static void check_web(object weburl)
{
bool isok;
isok = ConnectionAvailable(weburl.ToString());
}
public static bool ConnectionAvailable(string strServer)
{
try
{
strServer = "http://" + strServer;
HttpWebRequest reqFP = (HttpWebRequest)HttpWebRequest.Create(strServer);
reqFP.Timeout = 10000;
reqFP.Method = "HEAD";
HttpWebResponse rspFP = (HttpWebResponse)reqFP.GetResponse();
if (HttpStatusCode.OK == rspFP.StatusCode)
{
Console.WriteLine(strServer + " - OK");
rspFP.Close();
return true;
}
else
{
Console.WriteLine(strServer + " Server returned error..");
rspFP.Close();
return false;
}
}
catch (WebException x)
{
if (x.ToString().Contains("timed out"))
{
Console.WriteLine(strServer + " - Timed out");
}
else
{
Console.WriteLine(x.Message.ToString());
}
return false;
}
}
Just remember, you asked.
Very bad implementation.
Do not go creating threads like that. It does very little good to have more threads than processor cores. The extra threads will pretty much just compete with each other, especially since they're all running the same code.
You need to implement using blocks. If you throw an exception (and chances are you will), then you will be leaking resources.
What is the purpose in returning a bool? Do you check it somewhere? In any case, your error and exception processing are a mess.
When you get a non-200 response, you don't display the error code.
You're comparing against the Message property to decide if it's a timeout. Microsoft should put a space between the "time" and "out" just to spite you.
When it's not a timeout, you display only the Message property, not the entire exception, and the Message property is already a string and doesn't need you to call ToString() on it.
Next Batch of Changes
This isn't finished, I don't think, but try this one:
public static void Main()
{
// Don't mind the interpretation. I needed an excuse to define "rdr"
using (var conn = new SqlConnection())
{
conn.Open();
using (var cmd = new SqlCommand("SELECT Url FROM UrlsToCheck", conn))
{
using (var rdr = cmd.ExecuteReader())
{
while (rdr.Read())
{
// Use the thread pool. Please.
ThreadPool.QueueUserWorkItem(
delegate(object weburl)
{
// I invented a reason for you to return bool
if (!ConnectionAvailable(weburl.ToString()))
{
// Console would be getting pretty busy with all
// those threads
Debug.WriteLine(
String.Format(
"{0} was not available",
weburl));
}
},
rdr[0]);
}
}
}
}
}
public static bool ConnectionAvailable(string strServer)
{
try
{
strServer = "http://" + strServer;
var reqFp = (HttpWebRequest)WebRequest.Create(strServer);
reqFp.Timeout = 10000;
reqFp.Method = "HEAD";
// BTW, what's an "FP"?
using (var rspFp = (HttpWebResponse) reqFp.GetResponse()) // IDisposable
{
if (HttpStatusCode.OK == rspFp.StatusCode)
{
Debug.WriteLine(string.Format("{0} - OK", strServer));
return true; // Dispose called when using is exited
}
// Include the error because it's nice to know these things
Debug.WriteLine(String.Format(
"{0} Server returned error: {1}",
strServer, rspFp.StatusCode));
return false;
}
}
catch (WebException x)
{
// Don't tempt fate and don't let programs read human-readable messages
if (x.Status == WebExceptionStatus.Timeout)
{
Debug.WriteLine(string.Format("{0} - Timed out", strServer));
}
else
{
// The FULL exception, please
Debug.WriteLine(x.ToString());
}
return false;
}
}
Almost Done - Not Tested Late Night Code
public static void Main()
{
using (var conn = new SqlConnection())
{
conn.Open();
using (var cmd = new SqlCommand("", conn))
{
using (var rdr = cmd.ExecuteReader())
{
if (rdr == null)
{
return;
}
while (rdr.Read())
{
ThreadPool.QueueUserWorkItem(
CheckConnectionAvailable, rdr[0]);
}
}
}
}
}
private static void CheckConnectionAvailable(object weburl)
{
try
{
// If this works, it's a lot simpler
var strServer = new Uri("http://" + weburl);
using (var client = new WebClient())
{
client.UploadDataCompleted += ClientOnUploadDataCompleted;
client.UploadDataAsync(
strServer, "HEAD", new byte[] {}, strServer);
}
}
catch (WebException x)
{
Debug.WriteLine(x);
}
}
private static void ClientOnUploadDataCompleted(
object sender, UploadDataCompletedEventArgs args)
{
if (args.Error == null)
{
Debug.WriteLine(string.Format("{0} - OK", args.UserState));
}
else
{
Debug.WriteLine(string.Format("{0} - Error", args.Error));
}
}
Use ThreadPool class. Don't spawn hundreds of threads like this. Threads have such a huge overhead and what happens in your case is that your CPU will spend 99% time on context switching and 1% doing real work.
Don't use threads.
Asynch Call backs and queues. Why create a thread when the resource that they are all wanting is access to the outside world. Limit your threads to about 5, and then implement a class that uses a queue. split the code into two parts, the fetch and the process. One controls the flow of data while the other controls access to the outside world.
Use whatever language you like but you won't got wrong if you think that threads are for processing and number crunching and async call backs are for resource management.