I'm building a WPF data visualization tool with the Geared version of LiveCharts.
I have a SectionsCollection object named SectionsCollection that I need to reload as the data changes. I run the following code segment before reassigning to SectionsCollection.
try
{
if (SectionsCollection != null && SectionsCollection.Count > 0)
{
SectionsCollection.Clear();
}
}
catch(Exception e)
{
Status += "Error in clearing SectionsCollection.\n"+e;
}
SectionsCollection = new SectionsCollection();
The following error occurs intermittently on the SectionsCollection.Clear(); line, with the label NullReferenceException occurred.
Exception thrown: 'System.NullReferenceException' in LiveCharts.Wpf.dll
Additional information: Object reference not set to an instance of an object.
If I check that SectionsCollection is not null and is not empty, why is this error coming up?
This error seems to occur for VisualsCollection and SeriesCollection types as well.
Try add flag to prevent unwanted multiple exec. in your process:
bool collIsBusy = false;
try
{
if (SectionsCollection != null && SectionsCollection.Count > 0 && !collIsBusy)
{
collIsBusy = true; //flag to prevent throttling multiple executions
SectionsCollection.Clear();
collIsBusy = false;
}
}
catch (Exception e)
{
Status += "Error in clearing SectionsCollection.\n" + e;
}
SectionsCollection = new SectionsCollection();
Related
I have ASP.NET MVC application and I'm using a SqlDataAdapter for handling sql server methods. The method below returns nothing when an exception occurs, so I don't have any information when there is an error with a sql server command.
public int ExecuteNonQuery(string pSql, List<SqlParameter> prm)
{
SqlCommand cmd = new SqlCommand(pSql, sqlConnection);
int result = 0;
if (sqlConnection.State == ConnectionState.Closed)
{
sqlConnection.Open();
}
try
{
cmd.Parameters.AddRange(prm.ToArray());
result = cmd.ExecuteNonQuery();
return result;
}
catch (Exception ex)
{
return 0;
}
finally
{
sqlConnection.Close();
}
}
How can I asynchronously log exceptions without disrupting the user experience?Additionally, I want to log it to database and if there is a timeout exception then logging this timeout can get timeout again when logging.
There is no SqlDataAdapter code in your sample. That being said, there are three DataAdapter events that you can use to respond to changes made to data at the data source.
RowUpdating,
RowUpdated, &
FillError
There is also a:
Status property to determine if an error has occurred during the
operation and, if desired, to control the actions against the current
and resulting rows.
You can asynchronously log exceptions in those events when there is an error.
Examples from MSDN:
protected static void OnRowUpdated(
object sender, SqlRowUpdatedEventArgs args)
{
if (args.Status == UpdateStatus.ErrorsOccurred)
{
args.Row.RowError = args.Errors.Message;
args.Status = UpdateStatus.SkipCurrentRow;
Task.Run(() => LogError());
}
}
protected static void FillError(object sender, FillErrorEventArgs args)
{
if (args.Errors.GetType() == typeof(System.OverflowException))
{
// Code to handle precision loss.
//Add a row to table using the values from the first two columns.
DataRow myRow = args.DataTable.Rows.Add(new object[]
{args.Values[0], args.Values[1], DBNull.Value});
//Set the RowError containing the value for the third column.
args.RowError =
"OverflowException Encountered. Value from data source: " +
args.Values[2];
args.Continue = true;
Task.Run(() => LogError());
}
}
private void LogError()
{
// logging code
}
This code is being used to validate if an email exists in the database. The service return the values fine because it was tested with WCF Storm. In the code I am trying to call this method which return an object (validationResponse). If validationResonse has a true key I want to throw the ValidationException. What i think is happening is SL is making the call asyn and then moving one to he next line of code. How can I call a WCF method and get its reponse and act on it?
public string email
{
get
{
return _email;
}
set
{
vc.emailAddressCompleted += new EventHandler<emailAddressCompletedEventArgs>(vc_emailAddressCompleted);
vc.emailAddressAsync(value);
//Fails here with a null reference to vr (vr is declared futher up)
if (vr.isValid == false)
{
throw new ValidationException(vr.validationErrors);
}
this._email = value;
}
}
void vc_emailAddressCompleted(object sender, emailAddressCompletedEventArgs e)
{
//this never gets executed
this.vr = e.Result;
}
In silverlight all service calls are made asynchronously, in other words you can't call the service synchronously and wait for the reply. So what is happening in your code is vr is null and the exception is being thrown before the service call returns. You could change your code to something like this:
vc.emailAddressCompleted +=
new EventHandler<emailAddressCompletedEventArgs>(vc_emailAddressCompleted);
vc.emailAddressAsync(value);
//this while loop is not necessary unless you really want to wait
//until the service returns
while(vr==null)
{
//wait here or do something else until you get a return
Thread.Sleep(300);
}
//if you got here it means the service returned and no exception was thrown
void vc_emailAddressCompleted(object sender, emailAddressCompletedEventArgs e)
{
//should do some validation here
if (e.Error!=null) throw new Exception(e.Error.ToString());
vr = e.Result;
if (!vr.isValid)
{
throw new ValidationException(vr.validationErrors);
}
_email = value;
}
I've had this code working for at least a year and today it threw an exception that i haven't been able to figure out why its happening. Its a Forms.WebBrowser that hits a generic site first and then a secondary site.
'first site
wbr.ScriptErrorsSuppressed = False
wbr.Navigate("http://www.bing.com/?rb=0")
Do
Application.DoEvents()
Loop Until wbr.ReadyState = WebBrowserReadyState.Complete
'second site
wbr.ScriptErrorsSuppressed = True
Dim start As DateTime = DateTime.Now
Dim loopTimeout As TimeSpan = TimeSpan.FromSeconds(timeout)
wbr.Navigate("http://www.FlightAware.com")
Do
Application.DoEvents()
'loop timer
If DateTime.Now.Subtract(start) > loopTimeout Then
'stop browser
wbr.Stop()
'throw exception
Dim eExpTme As Exception = New Exception("A loop timeout occurred in the web request.")
Throw eExpTme
End If
Loop Until wbr.ReadyState = WebBrowserReadyState.Complete
The error happens on the second site access and it shows that it errors on the very last line with
System.UnauthorizedAccessException: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
at System.Windows.Forms.UnsafeNativeMethods.IHTMLLocation.GetHref()
at System.Windows.Forms.WebBrowser.get_Document()
at System.Windows.Forms.WebBrowser.get_ReadyState()
I just don't get why its errorring on the second site and not the first and what exactly that error message means. I've looked at some help forums but nothing concrete that i can use to troubleshoot.
AGP
The web site has a frame on ad.doubleclick.net, by default cross-domain frame access is disabled for the internet zone, so you get a security exception.
Catch the exception and move on. There isn't much you need to care about in the frame, doubleclick is an ad service.
You can implement IInternetSecurityManager and let IE to believe ad.doubleclick.net and FlightAware.com are the same web site, but this can cause security problem if you extend the trust to arbitrary web sites.
Here is a little hack in C# which you can convert in Vb.net:
public class CrossFrameIE
{
// Returns null in case of failure.
public static IHTMLDocument2 GetDocumentFromWindow(IHTMLWindow2 htmlWindow)
{
if (htmlWindow == null)
{
return null;
}
// First try the usual way to get the document.
try
{
IHTMLDocument2 doc = htmlWindow.document;
return doc;
}
catch (COMException comEx)
{
// I think COMException won't be ever fired but just to be sure ...
if (comEx.ErrorCode != E_ACCESSDENIED)
{
return null;
}
}
catch (System.UnauthorizedAccessException)
{
}
catch
{
// Any other error.
return null;
}
// At this point the error was E_ACCESSDENIED because the frame contains a document from another domain.
// IE tries to prevent a cross frame scripting security issue.
try
{
// Convert IHTMLWindow2 to IWebBrowser2 using IServiceProvider.
IServiceProvider sp = (IServiceProvider)htmlWindow;
// Use IServiceProvider.QueryService to get IWebBrowser2 object.
Object brws = null;
sp.QueryService(ref IID_IWebBrowserApp, ref IID_IWebBrowser2, out brws);
// Get the document from IWebBrowser2.
IWebBrowser2 browser = (IWebBrowser2)(brws);
return (IHTMLDocument2)browser.Document;
}
catch
{
}
return null;
}
private const int E_ACCESSDENIED = unchecked((int)0x80070005L);
private static Guid IID_IWebBrowserApp = new Guid("0002DF05-0000-0000-C000-000000000046");
private static Guid IID_IWebBrowser2 = new Guid("D30C1661-CDAF-11D0-8A3E-00C04FC9E26E");
}
// This is the COM IServiceProvider interface, not System.IServiceProvider .Net interface!
[ComImport(), ComVisible(true), Guid("6D5140C1-7436-11CE-8034-00AA006009FA"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
public interface IServiceProvider
{
[return: MarshalAs(UnmanagedType.I4)]
[PreserveSig]
int QueryService(ref Guid guidService, ref Guid riid, [MarshalAs(UnmanagedType.Interface)] out object ppvObject);
}
I have got a collection of viewModels(InputViewModel) in an other viewModel(ScenarioManager).
each InputviewModel has an instance of a Class(RestOfInput) which contains properties able to raise the OnPropertyChanged.
when one of these properties changes the event is handled by this method (in InputViewModel) :
public void TestAfterChanges(object sender, PropertyChangedEventArgs e)
{
MessageBox.Show("not ref");
bool isInTheList = false;
RestOfInput roi = sender as RestOfInput;
string prop = e.PropertyName;
if (prop!="NameFile")
{
Difference d = new Difference();
d.Length = prop;
d.Value1 = reference.RoI.getValueByPropertyName(prop);
d.Value2 = roi.getValueByPropertyName(prop);
foreach (Difference diff in _ListOfDifferences)
{
if (diff.Length==prop)
{
if ( (Math.Abs(d.Value2-d.Value1)>0.001*d.Value1))
{
//replace by le new one
_ListOfDifferences.Insert(_ListOfDifferences.IndexOf(diff), d);
_ListOfDifferences.Remove(diff);
}
else
{
//if change make the field value equal to the ref then remove from difference list
_ListOfDifferences.Remove(diff);
}
isInTheList = true;
}
}
if ((Math.Abs(d.Value2 - d.Value1) > 0.001 * d.Value1) && isInTheList==false)
{
_ListOfDifferences.Add(d);
}
}
}
this method gives just a summary of the differences between this particular case and the reference case.
Now if the reference case changes I have to update all the cases and the event is handled
in ScenarioManager :
public void refCaseChanging(object sender, PropertyChangedEventArgs e)
{
MessageBox.Show("ref");
string propname = e.PropertyName;
foreach (InputViewModel item in _casesList)
{
if (item!=inpVM)
{
item.RoI.OnPropertyChanged(propname);
}
}
}
inpVM is the reference case.
Then I have this behavior :
-if I change a field in a case which is not the reference case : everything is ok.
-if I change a particular field in the reference case : the first time, everything is ok.
But the second time, only the reference case and the first case (in the collection) which is not the reference case are updated>
It is like the foreach loop is broken..
Any explications.
If the message is not clear please tell me ( not easy to explain ;) )
An exception could explain that processing stops (although one expects that it would be caught and displayed somewehre).
Have you tried to ask VS to halt your program when an exception is thrown ? (if you have never done this before, go to Debug / Exceptions and check the check box for CLR exceptions)
I am working on an application that plays videos through the silverlight MediaElement object.
I have a large method which is responsible for the following
Opens a FileInfo item on the local file path of the video and strips the file name to get the first portion of the filename which we use as part of the license acquisition process
Sets the LicenseAcquirer on the MediaElement
Sets the Source property of the MediaElement
When this method is called, it actually causes the application to go into a "Not reponding" state for a couple of seconds. How do I avoid this? I have tried putting this all into a background worker but I have to invoke the UI thread for almost all of the calls and this didnt help it seemed to actually make things slower.
I have a busy box that shows while this all happens but that actually stops reporting progress in those seconds where the application is not responding. I understand why this is happening - a lot of work happening on the main UI thread, but how do I avoid this?
This is the code that is causing the trouble:
private void SetupMediaElement(String mediaElementType)
{
Messenger.Default.Send("Loading video...", "SetNowWatchingVideoBusyBoxText");
Messenger.Default.Send(true, "SetNowWatchingVideoBusyBox");
try
{
if (_mainMediaElement != null)
{
VideoItem vi = CurrentSession.NowPlayingVideoItem;
if (vi != null)
{
CurrentVideoItem = vi;
MustShowImage = true;
if (vi.ID != string.Empty)
{
String mediaId = String.Empty;
if (vi.LocalFilePath != DEMOVIDEOPATH)
{
if (vi.LocalFilePath != String.Empty)
{
var fi =
new FileInfo(vi.LocalFilePath);
if (fi.Exists)
{
mediaId = fi.Name.Substring(fi.Name.LastIndexOf('-') + 1,
(fi.Name.LastIndexOf('.') -
(fi.Name.LastIndexOf('-') + 1)));
}
}
else
{
Debug.WriteLine("localFilePath is empty");
}
Debug.WriteLine("MediaId = " + mediaId +
", SessionId = " +
CurrentSession.LoggedOnUser.SessionId +
",Ticket = " +
CurrentSession.LoggedOnUser.Ticket);
string licenseURL = GetLicenseURL(mediaId, CurrentSession.LoggedOnUser.SessionId,
CurrentSession.LoggedOnUser.Ticket);
if (licenseURL != string.Empty)
{
var la = new LicenseAcquirer
{
LicenseServerUriOverride
=
new Uri(
licenseURL)
};
la.AcquireLicenseCompleted += la_AcquireLicenseCompleted;
_mainMediaElement.LicenseAcquirer = la;
}
var fileInfo = new FileInfo(vi.LocalFilePath);
string playURL = #"file://" +
Path.Combine(CoreConfig.HOME_FULL_PATH, fileInfo.Name);
playURL = playURL.Replace("\\", #"/");
VideoURL = playURL;
}
else
{
VideoURL = vi.LocalFilePath;
Messenger.Default.Send(false, "SetNowWatchingVideoBusyBox");
}
_totalDurationSet = false;
TotalTime = FormatTextHoursMinutesSecond(_mainMediaElement.NaturalDuration.TimeSpan);
SetSliderPosition();
}
}
else
{
Messenger.Default.Send(false, "SetNowWatchingVideoBusyBox");
}
}
else
{
Messenger.Default.Send(false, "SetNowWatchingVideoBusyBox");
}
}
catch (Exception ex)
{
Debug.WriteLine(ex);
VideoURL = DEMOVIDEOPATH;
Messenger.Default.Send(false, "SetNowWatchingVideoBusyBox");
}
}
Thanks
EDIT:
So it turns out that the method posted above is NOT the cause of the delay - that code executes in under a second. The problem comes in when the media element's source is set and it reads the file to the end - large files take time and this is the delay. Am opening a new question based on this.
You should do some diagnostics to determine which line(s) are truely costing all that time, its unlikely that amount of time is spread evenly across the whole function.
Place that line (or lines) in a background thread (hopefully that line doesn't need to be on the UI thread).
So it turns out that the method posted above is NOT the cause of the delay - that code executes in under a second. The problem comes in when the media element's source is set and it reads the file to the end - large files take time and this is the delay. Am opening a new question based on this.