Develop Reference

Cannot access a disposed object but the program works

IN WPF project, whenever I try to add selected Student in selected university and display it on assoiated table.
Here is image of my table -
https://i.stack.imgur.com/KUHuF.png
I encounter this problem, once I hit update assosiated button.
public System.Data.Linq.Table<Student> Students
{
get
{
return this.GetTable<Student>();
}
}
The above code is in "Dataclasses1.designer.cs" window.
However, upon restarting the program, selected student is sucessfully added to selected university.
Here is my code -
private void UpdateAssociatedStudent_Click(object sender, RoutedEventArgs e)
{
if(ListUniversity.SelectedItem != null || ListStudent.SelectedItem != null)
{
using (dataContext = new DataClasses1DataContext())
{
UniversityManager universityManager = new UniversityManager
{
UniFK = int.Parse(ListUniversity.SelectedValue.ToString()),
StdFK = int.Parse(ListStudent.SelectedValue.ToString())
};
dataContext.UniversityManagers.InsertOnSubmit(universityManager);
dataContext.SubmitChanges();
}
ShowAssociatedStudents();
Sucess.Text = "Student is sucessfully added to University";
}
}
Edit - Adding image for error
https://i.stack.imgur.com/ApPxd.png

I think that you may need to change this line of code:
if(ListUniversity.SelectedItem != null || ListStudent.SelectedItem != null)
to
if(ListUniversity.SelectedItem != null && ListStudent.SelectedItem != null)

I've solved this issue by running try/catch instead of using 'Using' statement. my edited code looks like this.
//Add selected student from selected university in associated student listbox
private void UpdateAssociatedStudent_Click(object sender, RoutedEventArgs e)
{
if(ListUniversity.SelectedItem != null && ListStudent.SelectedItem != null)
{
try
{
uniManager = new UniversityManager()
{
UniFK = Convert.ToInt32(ListUniversity.SelectedValue),
StdFK = Convert.ToInt32(ListStudent.SelectedValue)
//UniFK = int.Parse(ListUniversity.SelectedItem.ToString()),
//StdFK = int.Parse(ListStudent.SelectedItem.ToString())
};
dataContext.UniversityManagers.InsertOnSubmit(uniManager);
dataContext.SubmitChanges();
ShowAssociatedStudents();
}
catch (FileNotFoundException)
{
Console.WriteLine("File Not Found.");
}
catch (OutOfMemoryException)
{
Console.WriteLine("Out of Memory.");
}
catch (IOException)
{
Console.WriteLine("An I/O error has occured.");
}
}
else
{
Failed.Text = "Please select the missing items from either university or student.";
}
}

Different behaviors when instantiated from button or timer in c#

I have a function called getMessages that can be called by a Button click (using the RelayCommand trigger) or that is called in a timer every 15s.
The desired behavior is:
webservice > deserialize answer > system notification > updatelistview > insert localDB
But when the function is called by the timer the updatelistview is not done. Why does this happen if the function is the same and works perfectly in the button command?
CODE:
// Get messages for the logged in user
public async void getMessages()
{
try
{
List<FriendGetMessage> msg = new List<FriendGetMessage>();
var response = await CommunicationWebServices.GetCHAT("users/" + au.idUser + "/get", au.token);
if (response.StatusCode == HttpStatusCode.OK) // If there are messages for me.
{
var aux = await response.Content.ReadAsStringAsync();
IEnumerable<FriendGetMessage> result = JsonConvert.DeserializeObject<IEnumerable<FriendGetMessage>>(aux);
if (result != null)
{
foreach (var m in result)
{
msg.Add(m);
}
//MsgList=msg;
foreach (var f in Friends)
{
if (f.msg == null || f.msg.Count() == 0)
{
f.msg = new ObservableCollection<Messages>();
}
foreach (var mess in msg)
{
if (mess.idUser == f.idUser)
{
Messages mm = new Messages();
mm.received = mess.message;
mm.timestamp = "Received " + mess.serverTimestamp;
mm.align = "Right";
// Add to the friend list.
f.msg.Add(mm);
// Add to Local DB
InsertMessage(null, au.idUser.ToString(), f.idUser, mess.message, mess.serverTimestamp);
var notification = new System.Windows.Forms.NotifyIcon()
{
Visible = true,
Icon = System.Drawing.SystemIcons.Information,
BalloonTipIcon = System.Windows.Forms.ToolTipIcon.Info,
BalloonTipTitle = "New Message from " + f.name,
BalloonTipText = "Message: " + mess.message,
};
// Display for 5 seconds.
notification.ShowBalloonTip(5);
// The notification should be disposed when you don't need it anymore,
// but doing so will immediately close the balloon if it's visible.
notification.Dispose();
}
}
}
counterChat = 1; // resets the counter
}
}
else {
counterChat = counterChat * 2;
}
//var sql = "select * from chat";
//var respo = GetFromDatabase(sql);
OnPropertyChanged("Friends");
}
catch (Exception e)
{
MessageBox.Show("GetMessages: " + e);
Debug.WriteLine("{0} Exception caught.", e);
}
}
CODE TIMER:
public void chatUpdate()
{
_timerChat = new DispatcherTimer(DispatcherPriority.Render);
_timerChat.Interval = TimeSpan.FromSeconds(15);
_timerChat.Tick += new EventHandler(timerchat_Tick);
_timerChat.Start();
}
public void timerchat_Tick(object sender, EventArgs e)
{
if (counterChat != incChat)
{
incChat++;
}
else
{
getMessages();
OnPropertyChanged("Friends");
incChat = 0;
}
}
ADDED - I've also tried this and didn't worked (it seems that is some kind of concurrency problem to the ObservableCollection called Friends (is a friendslist) each friend has an ObservableCollection of messages (is a chat))
public void chatUpdate()
{
_timerChat = new DispatcherTimer(DispatcherPriority.Render);
_timerChat.Interval = TimeSpan.FromSeconds(15);
_timerChat.Tick += new EventHandler(timerchat_Tick);
_timerChat.Start();
}
public async void timerchat_Tick(object sender, EventArgs e)
{
if (counterChat != incChat)
{
incChat++;
}
else
{
Application.Current.Dispatcher.Invoke((Action)async delegate { await getMessages(); });
incChat = 0;
}
}
Best regards,

I think you need to make the timer handler be an async method as follows:
public async void timerchat_Tick(object sender, EventArgs e)
{
if (counterChat != incChat)
{
incChat++;
}
else
{
await getMessages();
OnPropertyChanged("Friends");
incChat = 0;
}
}
This way OnPropertyChanged("Friends") is guaranteed to fire after the work in getMessages is done.
The methods need to change to:
DispatcherTimer _timerChat = new DispatcherTimer(DispatcherPriority.Render);
_timerChat.Interval = TimeSpan.FromSeconds(15);
_timerChat.Tick += new EventHandler(timerchat_Tick);
_timerChat.Start();
public async void timerchat_Tick(object sender, EventArgs e)
{
//...
await getMessages();
//...
}
public async Task getMessages()
{
try
{
// ... your code here
string result = await response.Content.ReadAsStringAsync();
// .... rest of your code
}
catch (Exception e)
{
MessageBox.Show("GetMessages: " + e);
}
}

It is solved. The problem was in my ViewModels I was opening multiple threads and sometimes the right one would update the UI and sometimes no.
Thanks for all the answers.

SearchBox result suggestion Windows 8.1

I got a strange issue with my searchBox in Windows 8.1 App.
I got an unhandler exception (and a crush) if in my Suggestion i do not append the querySuggestion and append only the ResultSuggestion.
the problem occurs when i change the queryText.
This is my function
public async void OnSuggest(Windows.UI.Xaml.Controls.SearchBox e, SearchBoxSuggestionsRequestedEventArgs args)
{
var deferral = args.Request.GetDeferral();
var queryText = args.QueryText != null ? args.QueryText.Trim() : null;
if (string.IsNullOrEmpty(queryText)) return;
TransporterExt tr_search = new TransporterExt();
tr_search.name = queryText;
try
{
var suggestionCollection = args.Request.SearchSuggestionCollection;
ObservableCollection<TransporterExt> querySuggestions = await TransporterService.Search(tr_search);
if (querySuggestions != null && querySuggestions.Count > 0)
{
foreach (TransporterExt tr in querySuggestions)
{
//if (tr.name.ToUpperInvariant().Contains(e.QueryText.ToUpperInvariant()))
//{
// //suggestionCollection.AppendQuerySuggestion(tr.name);
// suggestionCollection.AppendResultSuggestion(tr.name,
// tr.trId.ToString(),
// tr.trId.ToString(),
// imgRef, "imgDesc");
//}
suggestionCollection.AppendQuerySuggestion(tr.name);
}
}
}
catch (Exception)
{
//Ignore any exceptions that occur trying to find search suggestions.
}
deferral.Complete();
}
I got the searchBox inside an UserControl
My controller code
public delegate void SuggestionsRequested(Windows.UI.Xaml.Controls.SearchBox sender, SearchBoxSuggestionsRequestedEventArgs args);
public event Windows.Foundation.TypedEventHandler<Windows.UI.Xaml.Controls.SearchBox, SearchBoxSuggestionsRequestedEventArgs> SearchBoxSuggestionsRequested;
private void SearchBoxSuggestions(Windows.UI.Xaml.Controls.SearchBox sender, SearchBoxSuggestionsRequestedEventArgs args)
{
if (SearchBoxSuggestionsRequested != null)
SearchBoxSuggestionsRequested(sender, args);
}
I got this exception
WinRT: A method was called at an unexpected time.
exception: System.InvalidOperationException - type (string)
Edited Solution - Working function
First of all i remove from the constructor of the page the registration of event
public TruckCrudPage()
{
this.InitializeComponent();
this.navigationHelper = new NavigationHelper(this);
this.navigationHelper.LoadState += navigationHelper_LoadState;
this.navigationHelper.SaveState += navigationHelper_SaveState;
//this.truckForm.SearchBoxSuggestionsRequested += OnSuggest;
}
public async void OnSuggest(Windows.UI.Xaml.Controls.SearchBox e, SearchBoxSuggestionsRequestedEventArgs args)
{
var deferral = args.Request.GetDeferral();
TransporterExt tr_search = new TransporterExt();
ObservableCollection<TransporterExt> querySuggestions = new ObservableCollection<TransporterExt>();
var queryText = args.QueryText != null ? args.QueryText.Trim() : null;
if (string.IsNullOrEmpty(queryText)) return;
suggested.Clear();
tr_search.name = queryText;
try
{
var suggestionCollection = args.Request.SearchSuggestionCollection;
querySuggestions = await TransporterService.Search(tr_search);
if (querySuggestions != null && querySuggestions.Count > 0 )
{
int i = 0;
foreach (TransporterExt tr in querySuggestions)
{
if (tr.name.StartsWith(e.QueryText, StringComparison.CurrentCultureIgnoreCase))
//if (tr.name.ToLower().Contains(e.QueryText))
{
string name = tr.name;
string detail = tr.trId.ToString();
string tag = i.ToString();
string imageAlternate = "imgDesc";
suggestionCollection.AppendResultSuggestion(name, detail, tag, imgRef, imageAlternate);
suggested.Add(tr);
//Debug.WriteLine("dentro" + suggested.Count);
i++;
}
}
}
}
catch (Exception exc)
{
//Ignore any exceptions that occur trying to find search suggestions.
Debug.WriteLine("Exception generata " + exc.Message);
Debug.WriteLine(exc.StackTrace);
}
deferral.Complete();
}
But it works only with condition StartsWith and i would like to use Contains

You can use SearchBox and SuggestionRequested event to fire the event when type on the SearchBox. I will show an Example
<SearchBox x:Name="SearchBoxSuggestions" SuggestionsRequested="SearchBoxEventsSuggestionsRequested"/>
and write the SearchBoxEventsSuggestionsRequested handler in the code behind
private void SearchBoxEventsSuggestionsRequested(object sender, SearchBoxSuggestionsRequestedEventArgs e)
{
string queryText = e.QueryText;
if (!string.IsNullOrEmpty(queryText))
{
Windows.ApplicationModel.Search.SearchSuggestionCollection suggestionCollection = e.Request.SearchSuggestionCollection;
foreach (string suggestion in SuggestionList)
{
if (suggestion.StartsWith(queryText, StringComparison.CurrentCultureIgnoreCase))
{
suggestionCollection.AppendQuerySuggestion(suggestion);
}
}
}
}
You can add the keyword to SuggestioList, and it will show in the dropdown when you type on the Searchbox.
Create the SuggestionList
public List<string> SuggestionList { get; set; }
initialize the list
SuggestionList = new List<string>();
and add keywords to the list
SuggestionList.Add("suggestion1");
SuggestionList.Add("suggestion2");
SuggestionList.Add("suggestion3");
SuggestionList.Add("suggestion4");
SuggestionList.Add("Fruits");
When you type s on the Searchbox it will show all the keyword starts with s.
Thanks.

SearchBox windows App 8.1 , searching a substring "contained"

Building an App for windows store 8.1, i implement my searchbox, following the tutorial.
But, it works good only searching a substring that "startWith" another.
If i try to use something like "contains" i got a crush, an unhandled exception.
It works at the first, but if i change the query in the searchBox it crush ... often, not allways.
I can't understand the debugger message,because it refers to the app code...
That's my debugger message
Debugger:Debugger Break
A break in the debugger session because a user paused the session.
Time: 13/04/2014 12:34:34
Thread:<No Name>[6220]
and refers to
#if DEBUG && !DISABLE_XAML_GENERATED_BREAK_ON_UNHANDLED_EXCEPTION
UnhandledException += (sender, e) =>
{
if (global::System.Diagnostics.Debugger.IsAttached) global::System.Diagnostics.Debugger.Break();
};
#endif
}
my e object got an Exception : incorrect Parameter, handled : false....
that's my SuggestionRequested function, where there is the problem (i think)
public async void OnSuggest(SearchBox sender, SearchBoxSuggestionsRequestedEventArgs args)
{
var deferral = args.Request.GetDeferral();
TransporterExt tr_search = new TransporterExt();
ObservableCollection<TransporterExt> querySuggestions = new ObservableCollection<TransporterExt>();
var queryText = args.QueryText != null ? args.QueryText.Trim() : null;
if (string.IsNullOrEmpty(queryText)) return;
suggested.Clear();
tr_search.name = queryText;
try
{
var suggestionCollection = args.Request.SearchSuggestionCollection;
querySuggestions = await TransporterService.Search(tr_search);
if (querySuggestions != null && querySuggestions.Count > 0 )
{
int i = 0;
foreach (TransporterExt tr in querySuggestions)
{
string strB = sender.QueryText;
string strA = tr.name;
if(await Utility.Compare(strA,strB))
//using this condition all works fine
//if (tr.name.StartsWith(sender.QueryText, StringComparison.CurrentCultureIgnoreCase))
{
string name = tr.name;
string detail = tr.trId.ToString();
string tag = i.ToString();
string imageAlternate = "imgDesc";
suggestionCollection.AppendResultSuggestion(name, detail, tag, imgRef, imageAlternate);
if(tr!=null)
suggested.Add(tr);
i++;
}
}
}
}
catch (Exception exc)
{
//Ignore any exceptions that occur trying to find search suggestions.
Debug.WriteLine("Exception " + exc.Message);
Debug.WriteLine(exc.StackTrace);
}
deferral.Complete();
}
and the Contains utility
public static async Task<bool>Compare(string A, string B) {
bool contains = Regex.Match(A, B, RegexOptions.IgnoreCase).Success;
Debug.WriteLine("regex ="+contains);
return contains;
}
I got this SearchBox in a UserControl, and that's the code of my UC
public delegate void SuggestionsRequested(SearchBox sender, SearchBoxSuggestionsRequestedEventArgs args);
public event Windows.Foundation.TypedEventHandler<SearchBox, SearchBoxSuggestionsRequestedEventArgs> SearchBoxSuggestionsRequested;
private void SearchBoxSuggestions(SearchBox sender, SearchBoxSuggestionsRequestedEventArgs args)
{
if (SearchBoxSuggestionsRequested != null)
SearchBoxSuggestionsRequested(sender, args);
else
Debug.WriteLine("TruckFormUCException");
}
It's possible to search with another logic instead of "startswith"?... where's my fault?

Check tag for content with Overwrite warning

void device_DeviceArrived(ProximityDevice sender)
{
//Compatible Device enters area
if (stance == WriteStage.PREP)
{
System.Diagnostics.Debug.WriteLine("Writestages won");
//Perhaps here
updateStatusRectangle(Colors.Yellow);
stance = WriteStage.WRITING;
updateStatusText("Writing...");
writeToTag(msg);
}
else
{
updateReceivedText("Device connected!");
}
}
private void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message)
{
System.Diagnostics.Debug.WriteLine("Handler ran");
var rawMsg = message.Data.ToArray();
var ndefMessage = NdefMessage.FromByteArray(rawMsg);
foreach (NdefRecord record in ndefMessage)
{
System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length));
var specType = record.CheckSpecializedType(false);
if (specType == typeof(NdefTextRecord))
{
var textrec = new NdefTextRecord(record);
updateReceivedText(textrec.Text);
}
}
}
The above event and handler are executed when the phone comes into contact with an NFC device. For intents and purposes in this app, I need to ensure that before writing to a card, if it already has content, it will prompt the user to verify overwriting the data. I commented where I think it should go, but as far as checking for the Message, I'm not sure how to go about it. I can't call the handler without the ProximityMessage, and I don't know of another way to view the message.
The Question: Is it possible to call the MessageReceivedHandler (or check the message at all), from device_DeviceArrived?
(Note: Debug.Writelines are for test purposes, and this is just a quick NFC writer I'm throwing together).
UPDATE: In attempting to find a work around, I ran into a different problem.
public bool promptUserForOverwrite()
{
bool response = false;
Dispatcher.BeginInvoke(() =>
{
MessageBoxResult cc = MessageBox.Show("You are about to overwrite data. Proceed?", "Overwrite?", MessageBoxButton.OKCancel);
if (cc == MessageBoxResult.OK)
{
System.Diagnostics.Debug.WriteLine("MessageBox OK result");
response = true;
}
});
return response;
}
private void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message)
{
System.Diagnostics.Debug.WriteLine("Handler ran");
var rawMsg = message.Data.ToArray();
var ndefMessage = NdefMessage.FromByteArray(rawMsg);
foreach (NdefRecord record in ndefMessage)
{
System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length));
var specType = record.CheckSpecializedType(false);
if (specType == typeof(NdefTextRecord))
{
var textrec = new NdefTextRecord(record);
updateReceivedText(textrec.Text);
}
}
bool pow = promptUserForOverwrite();
if (!pow)
{
System.Diagnostics.Debug.WriteLine("Prompt returned");
//This always hits - pow is always false.
}
if (stance == WriteStage.WRITING && pow)
{
//writeToTag(msg);
}
}
This would work as a work around; the problem is the beginInvoke method. I need it for cross thread access, but used like this seems to make it run at a later time (when the thread is free?). The bool pow is always false, even after I click ok on the messagebox (debugged, and it does get the result, but after I can no longer use it). Is there an alternative that I can use for the Dispatcher?

Ugly, but I have this working. You need to get a TaskScheduler from the UI thread, so declare a
private TaskScheduler sched;
and then on the OnLoaded event for the page
sched = TaskScheduler.FromCurrentSynchronizationContext();
Then your methods
public async Task<bool> promptUserForOverwrite()
{
return false;
}
private async void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message)
{
System.Diagnostics.Debug.WriteLine("Handler ran");
var rawMsg = message.Data.ToArray();
var ndefMessage = NdefMessage.FromByteArray(rawMsg);
foreach (NdefRecord record in ndefMessage)
{
System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length));
var specType = record.CheckSpecializedType(false);
if (specType == typeof(NdefTextRecord))
{
var textrec = new NdefTextRecord(record);
updateReceivedText(textrec.Text);
}
}
var task = promptUserForOverwrite();
var pow = await task.ContinueWith(t =>
{
MessageBoxResult cc = MessageBox.Show("You are about to overwrite data. Proceed?", "Overwrite?", MessageBoxButton.OKCancel);
if (cc == MessageBoxResult.OK)
{
System.Diagnostics.Debug.WriteLine("MessageBox OK result");
return true;
}
else
{
return false;
}
}, CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, sched);
if (!pow)
{
System.Diagnostics.Debug.WriteLine("Prompt returned");
//This always hits - pow is always false.
}
if (stance == WriteStage.WRITING && pow)
{
//writeToTag(msg);
}
}