Programmatically Add Event Handler If It Doesn't Exist?
Oct 28, 2009
I'm trying to use a single event handler for several controls in an ASP.NET web page. I would like to add the event handler at runtime if and only if it doesn't already exist. In C#, I would write it as seen below:
if (myTextBox.OnTextChanged == null) myTextBox.OnTextChanged += DoTextChangingValidation;
Likewise, I know I can remove the event handler as follows:
if (myTextBox.OnTextChanged != null) myTextBox.OnTextChanged -= DoTextChangingValidation;
The event handlers in my parent class are never called though the events are raised in the child class.
The Code:
Public Class childForm Public Event checkboxchangedEvent(ByVal checkbox1 As Boolean, ByVal checkbox2 As Boolean) Private Sub checkboxchanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged, CheckBox2.CheckedChanged
remove an event handler from within the event handler?
I have a class that gets data from a hand scanner. When the scan is complete and the data is validated, the class fires a custom "ScanComplete" event and returns the data in a custom EventArgs.
In the calling program, I'm creating an instance of the scanning class and adding a handler for the "ScanComplete" event. In the event handler I get the data that was scanned and then remove the handler.
It seems to be working but it feels wrong to remove the handler while I'm running inside the handler. Will this cause a problem?
I have a Windows Form in which I started two threads and then close the form and threads continue their works. How can I abort first thread when the second thread stops?I made the first thread IsBackground,but the second thread is not the only thread of program and the first thread is started in another thread(form) that is closed and not exists anymore,in addition I can't set Flag of a Class that doesn't exist.
I have been trying to build the "Testing a class lesson, but the Set as StartUp Project line in the Project menu does not exist! I have redone the entire project 7 times, always the same response! # different computers, all with registered versions of VB. Why does this problem persist?
i read that WindowsFormsApplicationBase, is in the Microsoft.VisualBasic.ApplicationServices namespace
Do I have to really add the full-blown Microsoft.VisualBasic.ApplicationServices just to get WindowsFormsApplicationBase in c# ? What's the consequence on the size and performance of my c# app if I do so ?
It was there in VB 6. I have some images that I'm going to use a buttons, and I did this in VB 6 with the image control. however, this control doesn't appear to exist in VB.NET 2008 Express. I guess I could use a picture box, but isn't that overkill for such a simple task?
when people first run my program (as in the FIRST EVER time they run it), I want a window to popup (Form4). In this Form you have to locate a directory to a certain program (my program uses this program) and press OK, and then that will generate a .txt file with the directory to the program. (So that my program knows where that program is located.) Now, what I want it to do is when you open up the program, upon load (Form1), I want the program to check if that text file (directory.txt) exists. If it does and the path in the file is correct, the program will run fine. If the text file is missing and/or the directory doesn't exist, it will bring you back to Form4 (assuming that this is your first time running the program since the directory.txt file doesn't exist).
I want a message box to show when a username doesn't exist. I figured this would work but an error shows saying 'FileNotFoundException was Unhandled', for the fist line.
Dim UserFile As New System.IO.StreamReader(sPath & "" & UsernameBox.Text & ".txt") Username = UserFile.ReadLine Password = UserFile.ReadLine
I am trying to add a registry key in to the file "MyApp" which doesn't yet exist in the registry key directory, when I try and write this key however I get an error from the debug console telling me the "NullReference was unhanded". If I go and manually make this folder it works brilliantly, I thought that this code would make the folder as well?
What i need is, if a item in a listbox Doesn't exist, it needs to remove it from the other.
In the pic i have attached. Basically If it doesn't exist in Listbox2 then it needs to be removed from Listbox1 and tell the user which one has been removed.
i.e Test 02 doesn't exist. So messagebox would show "test02 has been removed" then remove it from listbox 1
It probably something simple thats sitting in the back of my mind, but for the life of me can't figure it out lol
I'm trying to complete this airline reservation application, but having a problem in this part of the question:Creat an event handler for the FlightBindingSource's PositionChanged event: select FlightBindingSource in the class Name combobox then select position changed in method name combobox to creat the FlightBindingSource's PositionChanged event handler. Write a code to access the currently displayed flight object and pass its flightNumber to method DisplayPassengers as a decimal.This Is my code so far:
HTML
Public Class AirlineReservationForm Private database As New ReservationsDataClassesDataContext() Private Sub FillAll()[code].....
I'm copying code from one VB project to another PC but the 'datagrid' on the copy insn't inserting into the new PC. When the form loads the datagrid is missing. The error I got was that there was something missing from the machine. When I tried to add the datagrid using the 'Additional Controls' it doesn't seem to exist. Any chance I can download the control? The version of VB is 6.5 and its part of a graphics package I'm using.
Mine is a simple conexion problem but I dont understands what's happening I have another form in the same project which has no problems at all, I desided to create a form to use it as a base form named plantillav only to duplicate forms and intance the others from that one I put it's Modifiers Property = Protected in ortder to modify property values in the other ones I don't know if the process generated a failure.
I created the following strconn:
Public
Class clientesc
[CODE]...
This table was exported from phpmyadmin (wamp) so it means is created and even with registers inserted directly from console, the problem is when I send from the application, with the following error that indicates that the name of the field doesn't exist or is not well written; Unknown column 'code_empleado' in 'field list'.
In this code block, the datarow gets the row number of the username that was used to log into the system with, right? And in this code, if there is a username/password that was matched with in the database, it'd place it on the dbUsername/dbPassword variables and compare it with the ones that were inputted by the user.What if I wanted to know if there is none of that username (like, username doesn't exist from the database)? I tried inputting login info that doesn't exist in the database and it resulted into the following error:An unhandled exception of type 'System.IndexOutOfRangeException' occurred in system.data.dll
Im developing a program that adds any number of tabs for each directory that contains user specified information and also adds a list view control on each tab that shows the files contained in said directories. I want the user to be able to double click a file in the list view(s) to open it.
I have this code in the onKeyDown event of the datagridview.
Private Sub DataGridView1_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles DataGridView1.KeyDown Select Case e.KeyCode[code]....
This works. When the Enter button is pressed, it acts as the TAB button.The problem I am having is this only works if the datagridviewer is selected.As soon as I enter data into a cell (A cell is selected) the code wont work as it is not set for the cell keyDown event. The event does not exist, so I have to somehow create it.
im trying to generate an error message to the user to let them know a file doesnt exist.So far ive got the user to enter the file name into a textbox, they click search and if successful will load a new form with a PDF file reader built in( AxAcroPDF1 )everytime i enter the right file name i get the file loaded, if enter the wrong name the File page still loads with no pdf and no message saying file doesnt exist.
Private Sub PictureBox1_Click(ByVal sender As System.Object, ByVal e
When I utilize AddHandler in VB to add my own method to the Click event :
AddHandler Button.Click, AddressOf myButton_Click
I see that my code executes last - after other event handlers for the Button_Click event. Is there a way to insert my event handler in front of other events so that it executes first?
I have recently published a simple text editor(just as an exercise). the editor has been published using Microsoft Visual Basic Express. Once the program is installed i wanted to make it a default opener for .txt files, so i clicked openwith ->Choose default program and then i was asked to show the location of the .exe. It seems like the .exe of my installed program doesn't exist. where the .exe is on a windows7 or tell me of another way of makeing that program the default opener.
I have got some code that is working as i have edited the game.exe at a certain address, now i know the code can find the address, but I don't know how to make it stop searching for it if it isn't there.
here is the:
code:
So what I want to know, is how to stop this code, if the address doesn't exist.
to know if a control have any handler. I have a dgv and in the editing control Showing event i add an event handler like this: VB AddHandler e.Control.KeyPress, AddressOf Grid_KeyPress_NumbersOnly This event it's added in some of the columns and for the other ones i remove it... The problem it's when the user, for example selects 3 columns where the event it's added, then if the user selects one where the event it's removed, it doesn't remove all handlers... So i have 2 solutions, when removing i put multiple removes or the other check if the event handler it's added doesn't add again. I prefer this second option, but i don't know how to check if the event it's added?
I'm using custom events activation/desactivation in one of my class. Let's say : AddHandler trv_treeview.BeforeExpand, AddressOf sub_LoadNextLevel and RemoveHandler trv_treeview.BeforeExpand, AddressOf sub_LoadNextLevel In another part of the code, I now need to know "Is there an event attached or not". In my search I found that Vb hold an hidden private variable <Eventname>Event. I've tried trv_treeview.BeforeExpandEvent but with no success. How is it possible, in Vb, to check how many Events are already attached to a method?
I've added the following code, however I get an error @ SendInput:
File I/O of a structure with field 'dwExtraInfo' of type 'IntPtr' is not valid Public Sub DoDoubleClick(ByVal wait As Integer, ByVal x As Integer, ByVal y As Integer)
