AccessViolation Exception Raised While Calling A VC++ Dll?
Jul 15, 2011
We are trying to call a VC++ unmanaged Dll from VB.net 4.0 application. During execution the application breaks and gives AccessViolationException(Unable to read or write protected memory). When we press F8, F10 or F5 it continues execution and give us correct results. And it is anonymous i.e. sometimes it works cleanly sometime it breaks. We tried everything ( debugging the Unmanged code, different ways to create unmanaged dll etc..).
Vc++ method signature: unsigned long LZCompressBuffer(unsigned char *SrcString, unsigned long SrcLen, unsigned char *DestString, unsigned long DestLen)
VB.net calling: Public Declare Function LZCompressBuffer Lib "CompExpand.dll" (ByVal buf() As Byte, ByVal slen As UInteger, ByVal dstr() As Byte, ByVal dlen As UInteger) As UInteger Mostly it generates error in memcpy() (String.h) method
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Mar 11, 2010
I have a class as below in VB.NET. The issue is class calling itself. So vb.NET throwing Stock Overflow exception. But the same class is working fine in VB6 version of code in VB6.How to resolve this issue?
[code]...
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Jun 2, 2010
I have code that's working beautifully on my development machine, but when deployed to the server is throwing null reference exception. So, I can't step through the code, but I've pinned down the culprit. But now I am puzzled.[code]In the code above persons is a dictionary of custom class, and certs is of IEnumerable type. Now here's the quandary.. The first line that sets the label returns False, so certs is not null. But the second line throws an null reference exception.
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Apr 3, 2009
I have done some reading and it seems that this error comes from recursive calls but I have not done anything in my form_closing handler except for call me.close, that's it.
So I don't understand how this exception has entered my project. All of my data and functionality is still working as I expect. It just seems to throw this exception when I try and exit my project.
what I could check to prevent something like this from happening?
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Jan 28, 2010
I have problem in calling DLL file in VB.Net that I had Created it in C++... it give me this error message: "An unhandled exception of type 'System.EntryPointNotFoundException' occurred in test_dll_1.exe. Additional information: Unable to find an entry point named 'add_1' in DLL 't1.dll'."
This is my code in C++ (header file)
[CODE]............
The one in the main
#include "header_1.h"
double add_1(double a, double b){
return (a+b);
[CODE].....................
This code only for creating dll and I did created it correctly and i had tested it in c++ and it did works.... but in the Vb.net I had no luck with it...This is the code that I wrote it in the VB.net
Imports System.Runtime.InteropServices
Public Class Form1
<DllImport("t1.dll")> Public Shared Function add_1(ByVal a1 As Double, ByVal a2 As Double) As Double
End Function
[CODE].....................
And, I did put the .dll file in the bin folder, but also with no luck...
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May 8, 2009
It is possible to catch an exception and throw a new exception which wraps the first exception as an inner exception: [URL] Also, if I call a function and it throws a certain error, but I catch it, will the calling code's catch handler execute? If so, and it is of a higher exception type, is this not wrapping the exception? eg I can throw exception ex of type IndexOutOfRange, log it but rethrow, catch a higher up exception and do something, or I can throw a new exception and wrap an inner exception like:
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Sep 7, 2010
This is the abstracted code for simplicity.
Public Class Form1
Dim WithEvents bt As New Button
Private Sub Bt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt.Click
MsgBox("Click")
[code]...
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Mar 9, 2010
I have an ASP.Net web user control which represents a single entry in a list. To allow users to reorder the items, each item has buttons to move the item up or down the list. Clicking on one of these raises an event to the parent page, which then shuffles the items in the placeholder control.Code fragments from the list entry:
Public Event UpClicked As System.EventHandler
Protected Sub btnUp_Click(ByVal sender As Object, ByVal e As System.EventArgs)
Handles btnUp.Click
[code]....
It originally looked in testing like every other time the value for sender (verified by its properties) that reaches UpClicked is of an adjacent ListItem, not the one I've just clicked on - the first click is always wrong, then the second for the correct control.At present,testing appears to show that the button's click event is just being ignored every other time through.Breakpoints on the click events within the control simply aren't being hit, though the events are definitely being established.
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Apr 5, 2011
I have read the documentation on RaiseEvent and Even but still confused. I am using a class that i call that performs a task on a thread.
vb
Public Property MyVar As String
Public Sub MuSub()
[code]....
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Aug 23, 2011
[code]But even here it seems the handler isn't registered until after New has completed.However, in real life the event is raised within code that's semantically part of the object initialisation, and I'd really rather not have to create some Initialize function.
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Apr 29, 2009
I'm working on a Windows Service that watches a few folders for changes, creations, and deletions. It all works well with the exception of one watcher that watches a single file (XML File with Configuration Settings) for minor changes.
I tried taking the Windows Service code and putting it into a simple windows application with start/stop buttons for the filesystem watchers and stepped through it. It never detects the file change of the XML config file. The changes are indeed occurring and the "Date Modified" of the file is updating.
XmlEventReferences = New System.IO.FileSystemWatcher()
XmlEventReferences.Path = "C:XmlReferences"
XmlEventReferences.Filter = "*.xml"
[Code].....
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Mar 13, 2012
I implemented the communication between two classes by using events in VB.Net.Now I want to store (record) all events that occure and to re-raise (replay) them again later.
Here is what I have already:
Class1:
Public Event Button1Pressed(ByVal sender As Object)
Private Sub btnButton_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnButton.Click
RaiseEvent Button1Pressed(Me)
End Sub
[Code]...
I could add another handler to the event I want to record, but then in the handler I only get the parameters that are passed to the event and not the event itself.Another thing I don't know how to solve is, that I can't raise an event from an extern class.
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Jul 27, 2010
I want to write an event that will simply display something when it is raised. I have never really worked with event driven programming before and am just trying to get a simple example working. It is not yielding any errors, but when I switch to debug mode I can see that the event it not raising correctly.
[Code]...
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Jan 11, 2012
I have a user control named "LettersDropControl". It has a dropdown list. I am using this control in a aspx page. When I change the selected item it is not calling the ddlLetters_SelectedIndexChanged event handler? What change I need to make in order to execute the code in ddlLetters_SelectedIndexChanged event handler?
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="LettersDropControl.ascx.cs" Inherits="MSAJAX1.LettersDropControl" %>
public partial class LettersDropControl : System.Web.UI.UserControl {
private string selectedLetter;
public string SelectedLetter {
[Code] .....
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Mar 2, 2011
I must be missing something really basic, but I just can't figure this out. I have a module (declared as a Module, i.e. a VB "static class") and I have an event declared in it, and places to raise the event. But I can't figure out how to handle the event.
Let's call the module MyModule with an even MyEvent. Like so:
Module MyModule
Public Event CallHelp()
Sub ExamineStuff( ByVal input As String)
[code]....
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Aug 5, 2011
I have an MDI application that can either run in TABBED or WINDOWED mode. When a user selects something from the menu a form is shown. All menuItem clicks pretty much look the same:
Dim frm As New <SomeForm>
frm.MdiParent = MDIParentForm
frm.Show()
[code].....
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May 12, 2011
I have a test class with an implementation similar to this:
public class MyObject Public Event testEvent(ByVal duh As Boolean)
Public Sub New()
'some code here
End Sub
[Code]...
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Oct 26, 2009
I discovered that an event raised (directly on indirectly) in the constructor cannot be handled outside the very class. To prove if that was the actual problem, I wrote a simple exemplary app.
Class with the event:
Namespace Utils
Public Class A
Public Event Test()
Public Sub New()
CallTest()
[Code] .....
The reason of such behavior became quite obvious after writing those pieces, but maybe there is a way to omit it?
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Jun 30, 2010
In a list of timers, how do I determine the index of the item that elapsed without having to iterate the collection as shown below (e.g. can I pass a paramater to OnTimedEvent, or can the collection raise an event to say which item fired???). It's the individual timer index that I need as I'm using it to refer to something else.
(I wont know how many items I'll have in the list in advance so I can't create an individual event handler for each timer - I don't think I should even if I did).
Public Class Form1
Private _timers As New List(Of System.Timers.Timer)
Private Sub Form3_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
[code]....
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May 2, 2009
I'm new to VB and relatively fresh in programming in general. I'm trying to write code to make a label flash red. The method involves using a timer. Problem is, it flashes, but I can't figure out how to make it stop. xD Here's my
Private Sub SeleneExplainsToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SeleneExplainsToolStripMenuItem.Click
lblNumbers.ForeColor = Color.Red
Timer1.Enabled = True
AddHandler Timer1.Tick, AddressOf OnTimerEvent
End Sub
[Code]...
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Jul 3, 2011
I want to raise an event from a non-UI thread where the event will be handled by the UI. Currently, I have to use .Invoke in my methods (which updates UI) called from the event.
How can I raise the event, similar to Background Worker's progress update event, where I don't have to specifically do an .Invoke for UI updates?
Do I wrap the event with a delegate or something? Sample code will be fine though, if the explanation was tedious.
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Nov 22, 2011
If you set a listbox selectedindex in code the SelectedIndexChanged event is only raised if the item isn't already selected, So why is the event rasied when you click a selected item with the mouse?
Here's what I came up with to get around the problem (which seems unnecessary and silly), So if there is a built-in or better way I'd sure like to know.
[Code]...
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Mar 22, 2010
A winforms dialog is using BackgroundWorker to perform some asynchronous operations with significant success. On occasion, the async process being run by the background worker will need to raise events to the winforms app for user response (a message that asks the user if they wish to cancel), the response of which captured in an CancelEventArgs type of the event.
Being an implementation of threading, I would have expected the RaiseEvent of the worker to fire, and then the worker would continue, hence requiring me to pause the worker until the response is received. Instead however, the worker is held to wait for the code executed by the raise event to complete.
It seems like method I am calling via the event call is actually on the worker thread used by the background worker, and I am surprised, since I expected to see it on the Main Thread which is where the mainform is running. Also surprisingly, there are no cross thread exceptions thrown.
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Dec 15, 2009
I'm currently designing an assembly that will be used by third parties. One of the classes has a long process of TCP connections and it informs about its process using events. For example
''# Do stuff that takes some time
RaiseEvent CompletedFirstPartEvent()
''# Do stuff that takes some time
[Code].....
What I've seen if that if the handler of one of those events takes too long (or even worse, it blocks) I can have timeouts and it's hard for the developer to see that one class is not working fine because his handler is taking too long.
I was going to fire the events in a new Thread to avoid this issue but this looks strange to me because I've never seen something like that, what I've seen until now is the developer spawning a new Thread if his handler was going to be timeconsuming. So the question is:
What would you do? Create a new thread or force the user to create his own thread? (Or is -there a better approach that I don't know?)
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Feb 28, 2010
I have a central page loading child controls into a container in a Silverlight Project.Problem is events like button click events are fired twice after processing the child forms.Suspect it might have something to do with a double initializecomponent??
Private Sub btVolgende_Click(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles btVolgende.Click
Select Case Stadium
[code].....
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Jul 12, 2010
I've been working with System.Drawing for awhile and like to think I have a good handle on it; I've created classes that draw grids, write text in gridboxes and rectangles, convert rectangles to circles, fill areas with color, etc. What I don't have is any sense of artistry at all, and I don't have the slightest clue how one would use System.Drawing to draw a rectangle and then color/slope the edges so that it looks like a System.Windows.Forms.Button would, or how to make it look like it's inset deeper than the surrounding Form, like setting a Panel's BorderStyle to Fixed3D.
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Nov 4, 2010
I have a User Control that has been added to the page dynamically. When I click a button on that user control[cod]e...
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Jun 2, 2010
I want to know what the Event has raised in a multi handler.
[Code]...
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Aug 2, 2011
I'm trying to capture the initial value of a listbox immediately after it's clicked on, and before the SelectedIndex is changed. The following was taken from: MouseDown in WinForm ListBox Kills SelectedIndexChanged, converted to VB. The ListBoxComponent Class is in a Component that shows at the top of the Toolbox.
Public Class ListBoxComponent
Inherits ListBox
Public Const WM_LBUTTONDOWN As Integer = &H201
Public Event PreSelect As EventHandler
[code]....
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Mar 11, 2010
I have login form as start up form and i call Form1 after successful validation and in Form1, i have close button on click of Close i would like to reset username and password fields on loginform to null. If i add code in form1 below i get exception Dim fmLogin As New LogInForm
An unhandled exception of type 'System.StackOverflowException' occurred in System.Windows.Forms.dll
Make sure you do not have an infinite loop or infinite recursion
I get above on LoginForm below statement Dim fmMain As New Form1
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