Need help with some VB.net coding (NOT C or c++)
So far I'm using this code to catch errors for specific line(s) of codes:
Try
bla bla bla
Catch ex As Exception
msbox("Error: " & ex.message)
End Try
But sometimes the application stops due to an error where I don't have a catch; how do I on occasions like this call upon a specific Sub (catch the error) for ANY OTHER error in the ENTIRE application where the Sub will display the error message (where I also plan on sending my self an e-mail in that sub to notify me application has stopped)?
I'm not sure if it will conflict with all current Try/Catch commands in my application, but I would prefer to only catch the error on code that currently is not within a Catch handler.
Thank you so much!
This functionality is built into the VB application framework, which is enabled by default in WinForms applications. Open the Application page of the project properties, click the View Application Events button and add a handler for the UnhandledException event using the navigation bar at the top of the code window. Done!
The VB application framework hides some of the complexity of applications that you must implement yourself in C#. It includes a Startup event that you can handle instead of adding code to a Main method, a StartupNextInstance event to support single-instance apps with commandline arguments, multi-threaded splash screen functionality and more.
Regarding your emailing idea, just sure to add in a privacy notice before auto-emailing yourself anything in your apps; this can be a big bone of contention to users, & if an astute one catches it silently phoning home your rep is down the drain.
As for a global error handler, have a look here:
https://www.dotnetcurry.com/patterns-practices/1364/error-handling-dotnet-projects
Related
Is there a simple way to catch all exceptions in your VB.NET applications? I'm interested in making it so that instead of my users seeing a runtime error, they just are told that an error occurred and to contact tech support, then the relevant error information is logged so our support team can look at it afterwards.
You can use the OnUnhandledException application event to catch (almost) every exception that wasn't handled by the code.
On the Project Properties window (double-click project file on the solution explorer or Project Menu -> [Project name] properties), the Application page has a "View Application Events" button that creates a new file in your project.
In that file there are some events that are fired at application level; one of those is the UnhandledException. Whatever you put there will be executed instead of the classic JIT dialog. The UnhandledExceptionEventArgs object has an Exception property with the unhandled exception object, and a ExitApplication property that decides if the application should exit or continue executing.
Namespace My
' The following events are available for MyApplication:
'
' Startup: Raised when the application starts, before the startup form is created.
' Shutdown: Raised after all application forms are closed. This event is not raised if the application terminates abnormally.
' UnhandledException: Raised if the application encounters an unhandled exception.
' StartupNextInstance: Raised when launching a single-instance application and the application is already active.
' NetworkAvailabilityChanged: Raised when the network connection is connected or disconnected.
Partial Friend Class MyApplication
Private Sub MyApplication_UnhandledException(sender As Object, e As Microsoft.VisualBasic.ApplicationServices.UnhandledExceptionEventArgs) Handles Me.UnhandledException
MessageBox.Show(e.Exception.ToString) '<-- the exception object
e.ExitApplication = True '<-- True if you want the application to close; false to continue - if it can
End Sub
End Class
End Namespace
Note that there are still some "über-exceptions" that can't be caught even with this method (out of memory for example), but this way you can log what exceptions are not being correctly handled on your code, or what scenarios are actualy happening that weren't considered at the beggining.
More info here
As a side note: don't rely too much on this event. This has to be for extremely exceptional cases, as what is caught here should be treated ASAP in the corresponding class/module/method. This is a helpful tool for debugging and test cases but having too much exceptions being handled by this event would be a sign of something wrong in your code.
It depends on what environment your application is running in. If you are using WPF or WinForms, you would launch your application using a main method instead of directly launching a form or page. Your main method should then wrap the calls to instantiate the UI in a try catch block.
So, for a WinForms Application, you could do something like this:
Sub Main
Try
Dim MainUI As New Form1
MainUI.Show()
Application.Run
Catch ex As Exception
'Do that fancy exception processing
End Try
End Sub
You can do something similar with WPF. But, WPF also supports an event model where you are notified of exceptions, very similar to the one that ASP.Net uses.
You will never be able to catch the StackOverflowException.
All the others for sure yes. I'm not familiar with VB, but it is easy to achieve in C#. For VB, I think the generic exeption handler could be
Try
...
Catch e As Exception
...
End Try
Of course this has to wrap all your code. You can find more for examples here.
If you have forms application, it is not practical to have the handler around Application.Run() as the only event handler. Keep it there, but add also two others:
When inside the form, and exception occurs, you want to keep execution in that context – keep the form open etc. For this purpose, use ThreadExceptionEventHandler.
And also, for case when application is irrepairably crashing on some problem, add handler to Dispatcher.UnhandledException event. It is last thing executed before the application ends. You can log the exception to disk for later investigation etc. Very useful.
Let's see some good resource how they are applied.
I'm creating an add-in for Solidworks EPDM (example from API help). This is a class library (.dll) project which is added to EPDM and allows some custom functions to be added to the program.
I want to add logging for unhandled errors so that when an exception is caused by my add-in (as opposed to by the Solidworks EPDM program itself) I can be notified of it and try to fix it.
I'm quite new to all of this (and by all of this I mean VB.NET as a language, programming anything other than macros in VBA, structured exception handling, error logging, etc) and I'm trying to follow MSDN How To: Log Exceptions in Visual Basic but the instructions for logging unhanlded exceptions don't seem applicable to class library projects.
Specifically, I don't know how to get past step 3:
To log an unhandled exception
1. Have a project selected in Solution Explorer. On the Project menu, choose Properties.
2. Click the Application tab.
3. Click the View Application Events button to open the Code Editor.
This opens the ApplicationEvents.vb file.
The View Application Events button is greyed out for class library projects.
So, is there another way to add logging for unhandled exceptions in class library projects? Or, another way to access the ApplicationEvents.vb file for class library objects? I've tried searching for either, and have yet to find a solution that would allow me to log unhandled exceptions.
This is a very basic example but wrap your code with Try/Catch in the only two interface methods (host "callbacks") that IEdmAddIn5 defines and which your add-in class must implement.
Public Sub GetAddInInfo(ByRef poInfo As EdmAddInInfo, ByVal poVault As IEdmVault5, ByVal poCmdMgr As IEdmCmdMgr5) Implements IEdmAddIn5.GetAddInInfo
Try
...
Catch ex As Exception
' Handle exception...
End Try
End Sub
Public Sub OnCmd(ByRef poCmd As EdmCmd, ByRef ppoData As System.Array) Implements IEdmAddIn5.OnCmd
Try
...
Catch ex As Exception
' Handle exception...
End Try
End Sub
I would ordinarily agree with #Hans Passant about re-throwing the exception but I generally have found that to be problematic with an EPDM add-ins as it can cause the COM host to crash.
I am recently out of school, working my first job as a programmer. We have a user-reported bug that is occurring when our application timeout timer closes the application. I'm pretty sure I've narrowed it down, but am curious as to why the original programmer would have done this, if it's good coding practice, and if so, I am curious if anyone has a way to handle this. We are getting a post-closing system error, as it occurs after the main form closes, so we don't get any exception log input.
The close functionality of the timeoutTimer_tick handler does the following:
For iCount As Int16 = Application.OpenForms.Count - 1 To 0 Step -1
Try
Application.OpenForms(iCount).Close()
Catch
End Try
Next
Try
Application.Exit()
Catch ex As Exception
End Try
The program is set with the application property to close when the main form closes (not ALL open forms are closed). This makes me wonder why we're looping through each form and closing them individually, and then calling Application.Exit()
I'm pretty sure our error is because of the Application.Exit call after all open forms are closed. It doesn't see the main form, as it was closed during the loop, and throws an error. I feel like we should be using one or the other, but not both.
Any input or advice? Which is better, or are either better (or should this code work without error, and I am simply wrong).
Thanks
In WinForms you have a Shutdown Mode setting (Project Properties>Application Tab)
This allows you to specify When startup form closes or When last form closes
So logically you should not need Application.Exit .If you do then there is some other object hanging around in memory that you need to dispose of (something started on a thread / background worker etc)
So If you have the startup form setting:
[StartupFormName].Close
or if you have the last form setting:
Do While My.Application.OpenForms.Count > 0
My.Application.OpenForms(0).Close()
Loop
We have an application that allows custom UI and interaction via SDK.
A DLL is developed for this purpose using VB.Net and the SDK.
An object variable refers to the application and there are some other object variables for components within the application.
Application allows assigning VBScript code to button(s) displayed in toolbar. The VBScript code is:
Dim Utility_Main
Set Utility_Main = CreateObject("Utility.Application")
Utility_Main.Launch()
This launches a form (custom UI) and users can interact with the application via this form.
Although application itself has its own UI, this utility form is created for database lookup, preserving certain attributes of application objects etc.
In just about every exit point of the form, a procedure is called to unset object variables for application and its components using following code:
========================================
Try
Marshal.ReleaseComObject(objX)
Catch
End Try
Try
objX = Nothing
GC.Collect()
Catch
End Try
Note1: ReleaseComObject and setting object variable to Nothing was wrapped in "If (Not objX is Nothing) Then". But it was changed to above format to make sure it gets called.
Note2: GC.Collect was added later to force GC.
========================================
This is done for each object in reverse order of object hierarchy.
Application's executable (Application.exe) remains loaded in both of the following cases:
Application is closed first and then Utility form is closed
Utility form is closed first and then the application is closed
The only time "Application.exe" goes away is if Application is closed first and then Utility form is closed by clicking on "End Task" in Task Manager.
Any help will be greatly appreciated.
I realize you say that it was split up for some reason, but this should be:
Try
If objX IsNot Nothing Then
Marshal.ReleaseComObject(objX)
End If
Catch e As ArgumentException
' hopefully you have some debug output here
Finally
objX = Nothing
GC.Collect() ' really doubt this is necessary
End Try
This guarantees that objX is released if it is not Nothing, and if that throws an exception (note the list of exceptions), then you can catch it and figure out what happened. Whether or not an exception is thrown, objX will be set to Nothing and the GC will be invoked.
It's probably not this code that is causing your program to stay open. You will need to show more code (how they interact, or any non-daemon threads that you may manually start will also be to blame). It sounds like Utility is forcing the Application to stay alive with a non-daemon, background thread, but it really could be the other way around, and it could be the case that doing that in both directions.
I get an application error thrown when I close the program using as cancel button which all it does is close the form.
The error says:
"Application appName.exe encountered a serious error and must shut down"
How do I start fixing it? It is not a thrown exception; no other info is given.
What could it be and how do I fix it?
Here is what it was. My application has two forms - login and main form where all the action happens. The login form has two buttons (Login and Cancel). Login button logs user in, closes the login form and opens the main form. Cancel button just closes the login form. To close the form I simply used this.Close().
What was happening though is that I still needed to dispose of the login form explicitly by doing something like:
frmLogin.Dispose();
frmLogin = null;
before exiting the program (in my Program.cs)
So this solved it. I had to make sure that this was being done in both cases: when the user logs in as well as when they choose to not log in.
Crucial fact is that frmLogin is modal, hence Dispose() is not called automatically when closed.
This is typically caused by a system-level exception in your process space that managed code is unable to catch. Typically it happens when you P/Invoke out to native code and give it a bad pointer/parameter and it causes a native exception that is uncaught by the CLR.
Throw a try/catch block around the Application.Run(...) line in your Program.cs, like this:
try
{
Application.Run(new Form1());
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
The message you're seeing means there's a thrown exception that isn't being caught.
Look at some GUI components, DLLs or port resources. Some time is unclosed port, some time some GUI component (i deal with some List GUI component)
I had resharper installed and its cache was creating issue. I deleted the cache and it worked.