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We are currently in the process of updating our database system and all of the files by building them(32bit-2005 VC#) to 64 bit now. Something I've come across is the leaking of data when an assignment using this.closing += new CancelEventArgs(Event Name); I've found it to be obsolete as fellow colleagues have put it and am looking for a way to switch to using the FormClosing event.
...
Old Code and Event Ex.
this.Closing += new CancelEventHandler(AssignUsers_Closing);
private void AssignUsers_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
try
{
"some event"
}
catch (Exception ex)
{
ShowException se = new ShowException();
se.ShowDialog(ex);
}
}
This is where I'd like to convert to the FormClosing Event so that windows can take care of the data leak for me rather than having to add a -= statement for each event like this to the .dispose() function.
Idea/New Code
private void AssignUserForm_FormClosing(object sender, FormClosingEventArgs e)
{
try
{
*code*
// Use e.cancel to test whether to close the form or not.
}
catch (Exception ex)
{
ShowException se = new ShowException();
se.ShowDialog(ex);
}
}
Would this be a viable alternative. Any suggestions on how to make this change?
EDIT: BETTER OVERVIEW OF MY QUESTION
Changing this:
public AssignUserForm()
{
InitializeComponent();
InitMe();
try
{
Database.ApplyFieldSecurity(this);
}
catch { }
}
private void InitMe()
{
try
{
this.Closing += new CancelEventHandler(AssignUsers_Closing);
// Get the users from the system
//Binding happens
}
catch (Exception ex)
{
throw ex;
}
}
Turning it into something where I can use Windows Events to simply create a FormClosing event.
The problems were solved. There was a data leak occurring between our database and when the control that this dialog belonged to were loading. I appreciate all of the help. The database shot over the information before the dialog loaded, and then would send it over again. Only one set of the data was properly disposed of. We fixed the problem. Thank you. –
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I'm writing a program on C# and I'm just starting on using Exception. I've done Java before but I tried to avoid exception at any cost. I understand now that I can't avoid it any longer. So I need some advice. I have a code like this:
try
{
//...
}
catch
{
//...
}
//...
try
{
//...
}
catch
{
//...
}
This is a GUI program. I want to make it so that if an exception is caught, the program will basically stop all operation and but not close the program, so the GUI is still there, users can make changes to the problem found.
BTW: Our lecturer will fail us for multiple returns, so that advice won't do
You can define a handler to catch all unhandled exceptions. The exact mechanism depends on the UI framework you are using.
For WinForms you can do something like
AppDomain.CurrentDomain.UnhandledException += new
UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
// Windows forms exceptions handler
Application.ThreadException += new
ThreadExceptionEventHandler(Application_ThreadException);
http://kenneththorman.blogspot.com/2010/10/windows-forms-net-handling-unhandled.html
For WPF you would do something like
<Application x:Class="UnhandledExceptionHandler.App"
DispatcherUnhandledException="Application_DispatcherUnhandledException">
</Application>
private void Application_DispatcherUnhandledException(object sender,
System.Windows.Threading.DispatcherUnhandledExceptionEventArgs e)
{
// Handle the exception
}
http://www.codeproject.com/Articles/90866/Unhandled-Exception-Handler-For-WPF-Applications
Just in case Eric J.'s answer is too involved:
I assume since your prof will only permit one return statement that you will have something like a service that does some work and notifies the caller of the status and possibly an error message.
If you can get by with boolean messages, then the following should work for you:
public class Service
{
public bool DoWork()
{
bool success = false;
try
{
//code to do work
success = true;
}
catch(Exception ex)
{
//do something with the ex
success = false;
}
return success;
}
}
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I am trying to learn programming and I am starting with a book called Software Development Fundamentals. However I am having loads of difficulty understanding certain subjects. Especially because my native language is not English. I am stuck at the subject (events) and (delegates). I feel like this is to difficult for me, I can not even get this code to work!
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Lesson02
{
class Program
{
static void Main(string[] args)
{
Rectangle r = new Rectangle();
r.Changed += new EventHandler(r_Changed);
r.Length = 10;
}
static void r_changed(object sender, EventArgs e)
{
Rectangle r = (Rectangle)sender;
Console.WriteLine(
"Value Changed: Length = {0}",
r.Length);
}
}
class Rectangle
{
public EventHandler Changed;
private double length;
public double Length
{
get
{
return length;
}
set
{
length = value;
Changed(this, EventArgs.Empty);
}
}
}
}
I get this error:
Error 1 The name 'r_Changed' does not exist in the current context 14 59 Lesson02
C# is case-sensitive language. You have defined function as r_changed and using it as r_Changed
Use
r.Changed += new EventHandler(r_changed);
instead of
r.Changed += new EventHandler(r_Changed);
I'm pretty sure you'd know by now that C# is a case sensitive programming language.
This should work
static void r_Changed(object sender, EventArgs e)
{
Rectangle r = (Rectangle)sender;
Console.WriteLine("Value Changed: Length = {0}", r.Length);
}
Notice how r_Changed is capitals (r_changed is what you originally defined)
I would suggest using this because it is easier to read.
There is a little typo mistake in your code. It should be r_Changed instead of r_changed in the your Event Handler.
i.e write
static void r_Changed(object sender, EventArgs e)
in place of
static void r_changed(object sender, EventArgs e)
(Remember C# is Case-sensitive)
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i'm new to winform and i can't figure out how to use the BackgroundWorker.
basically what i'm trying to do is this:
i have 1 form with 2 buttons: "Import" and "Exit" . when calling ImporButton_Click all it does is creates an HttpListener and listen to a given URL. ExitButton_Click closes the form.
the problem is when i press "Import" the form get stuck and it's in "not responding" status until someone is calling the listener and free it.
i'm trying to under stand how BackgroundWorker can help me to overcome that "stuck" problem. i don't understand how to invoke the backgroundWorker1_DoWork method
Here is my code so far:
//Program.cs
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new ConfigurationForm());
}
}
//ConfigurationForm.cs
public partial class ConfigurationForm : Form
{
public ConfigurationForm()
{
InitializeComponent();
UrlTextBox.Text = #"enter URL here";
}
private void ImporButton_Click(object sender, EventArgs e)
{
try
{
String urlToListen = UrlTextBox.Text;
//Invoke MyListener
MyListener.StartListen(urlToListen); //assume this is implemented
}
catch (Exception exception)
{
string errorMsg = String.Format("An exception occured = {0}", exception);
MessageBox.Show(errorMsg);
}
}
private void ExitButton_Click(object sender, EventArgs e)
{
this.Close();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
}
}
so, what now ? how do i invoke the backgroundWorker1_DoWork ???
10x to anyone who can help
You need to call this method RunWorkerAsync
backgroundWorker1.RunWorkerAsync();
If you want to pass some argument into the handler DoWork via the DoWorkEventArgs, try the second overload of RunWorkerAsync:
backgroundWorker1.RunWorkerAsync(yourArgument);
I have a code like this in VS 2012:
private void Form1_Load(object sender, EventArgs e)
{
if (Properties.Settings.Default["Database"] != null)
{
MessageBox.Show("We landed on spot 1");
}
else
{
MessageBox.Show("We landed on spot 2");
}
}
I'm pretty sure I messed up the condition syntax, but I would expect that one of these would happen:
Compiler warns about errors/project fails to run.
First message is shown
Second message is shown.
But neither of these actually happens. I've been staring at this for an hour and resources I could find are pretty slim.
If anyone with an experience could explain me what actually happens here?
Edit:
Thanks to JMK's link I found out this is basically a wontfix bug popping up in VS debugger under Windows x64. Error fires if application is run outside of debugger.
Its silently erroring.
try
{
if (Properties.Settings.Default["Database"] != null)
{
MessageBox.Show("We landed on spot 1");
}
else
{
MessageBox.Show("We landed on spot 2");
}
}
catch (Exception ee)
{
MessageBox.Show(ee.Message);
}
Comes back with "The settings property 'Database' was not found"
Try adding your project namespace before the Properties
if (WindowsFormsApplication2.Properties.Settings.Default.Database != null)
Propably an exception is thrown and not noticed by the debugger.
This happens for Windows Forms projects on 64bit Windows Versions (and is not a behaviour specific to .NET but to Windows in general).
More details here: Visual Studio does not break at exceptions in Form_Load Event
Try pressing STRG + ALT + E and mark the checkbox "Thrown" for "Common Language Runtime Exceptions".
Now the debugger will break on any exception in Form_Load()
Since I know about that my workaround is to completly avoid using the Load event.
Most of my Forms are Dialogs so I shadow the ShowDialog() method and call a Init() function.
public class Form1
{
public new DialogResult ShowDialog()
{
Init();
return base.ShowDialog();
}
public new DialogResult ShowDialog(IWin32Window owner)
{
Init();
return base.ShowDialog(owner);
}
public void Init()
{
// code goes here
}
}
we're having an application on server instance and quite rarely, but we have out of memory exception (program is not leaking, just instance is quite small and it operates with quite big amounts of data).
That would be not a problem, as we monitor processes on that server instance and if some of the processes are not found in process list, alert email is sent.
Now the problem is with this:
That prevents process from disappearing from process list, so we don't get alert email about it's failure. Is it possible to disable this message, that if program fails on something we don't catch, it would close without user interaction?
Assuming Windows Forms, I typically do multiple steps to prevent this message box.
First, I connect several handlers in the Main function:
[STAThread]
private static void Main()
{
Application.ThreadException +=
application_ThreadException;
Application.SetUnhandledExceptionMode(
UnhandledExceptionMode.CatchException);
AppDomain.CurrentDomain.UnhandledException +=
currentDomain_UnhandledException;
Application.Run(new MainForm());
}
Those handlers are being called when an otherwise unhandled exception occurs. I would define them something like:
private static void application_ThreadException(
object sender,
ThreadExceptionEventArgs e)
{
doHandleException(e.Exception);
}
private static void currentDomain_UnhandledException(
object sender,
UnhandledExceptionEventArgs e)
{
doHandleException(e.ExceptionObject as Exception);
}
The actual doHandleException function that is then called does the actual error handling. Usually this is logging the error and notifying the user, giving him the options to continue the application or quit it.
An example from a real-world application looks like:
private static void doHandleException(
Exception e)
{
try
{
Log.Instance.ErrorException(#"Exception.", e);
}
catch (Exception x)
{
Trace.WriteLine(string.Format(
#"Error during exception logging: '{0}'.", x.Message));
}
var form = Form.ActiveForm;
if (form == null)
{
MessageBox.Show(buildMessage(e),
"MyApp", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
else
{
MessageBox.Show(form, buildMessage(e),
"MyApp", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}
With the helper function:
public static string buildMessage(Exception exception)
{
var result = new StringBuilder();
while (exception != null)
{
result.AppendLine(exception.Message);
result.AppendLine();
exception = exception.InnerException;
}
return result.ToString().Trim();
}
If you are using not Windows Forms but e.g. a Console application or WPF, some handlers are not present, while others are present instead.
The idea stays the same: Subscribe to event handlers that are being called if you have no try...catch around your code blocks.
Personally, I try to have as few of those try...catch blocks as possible (ideally none).
don't know if you can deactivate this - but I think you should not.
Find the bug/problem in your application and handle the problem with a craceful shutdown or by preventing the problem in first case.
Everything else will be a real crude workaround and I don't think your client will be pleased to have such a behavior (after all won't there be data lost? If not this has allways the buggy / not finished touch)
You could put a global try/catch block in your program and exit the program on any unexpected exception.
If using WPF you can try-catch the following two exceptions in your app.xaml.cs. There may be other/complementary exceptions to handle, but this are the two I am usually looking for:
AppDomain.CurrentDomain.UnhandledException - "This event provides notification of uncaught exceptions. It allows the application to log information about the exception before the system default handler reports the exception to the user and terminates the application. If sufficient information about the state of the application is available, other actions may be undertaken — such as saving program data for later recovery. Caution is advised, because program data can become corrupted when exceptions are not handled."
Dispatcher.UnhandledException - "Occurs when a thread exception is thrown and uncaught during execution of a delegate by way of Invoke or BeginInvoke."
ie:
public partial class App : Application
{
public App()
{
this.Dispatcher.UnhandledException += DispatcherUnhandledException;
AppDomain.CurrentDomain.UnhandledException += CurrentDomainUnhandledException;
}
private void CurrentDomainUnhandledException(object sender, UnhandledExceptionEventArgs e)
{
// log and close gracefully
}
private new void DispatcherUnhandledException(object sender, System.Windows.Threading.DispatcherUnhandledExceptionEventArgs e)
{
e.Handled = true;
// log and close gracefully
}
}