I'm having trouble wrapping my head around Events and their Handlers in general. I was working from some sample code that used them, and I can't understand why use an event rather than simply using a sub. I'm absolutely sure I'm missing the bigger picture here.
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The Event allows a class to say 'Do something when this happens' in a very ambiguous way, leaving the class which created the Object to define a Handler; what that action should be. That Handler can, and very likely will, be unique to each instance of the class.
It seems to me that this would likely be achievable (on a basic level) through indexing and enumeration, but that would get messy and become a lot of code to write rather quickly. This is probably a much more flexible and extensible way of handling things. I'm going to post this anyway, in the hopes that I'll get someone to tell me whether I am correct in my observations or totally off base, and that it helps someone else who is having trouble with this concept as they dip their toes into OOP and event driven objects.
Possible Duplicate: In C#, should I use string.Empty or String.Empty or "" ? I just don't understand the benefits of using String.Empty over "". Aside it being strongly typed its longer.
I'm dynamically adding an event handler on a link button, first when the page is load o create a link button with product category. On clicking the product category it fires an event and passes the product-id IN sender object.
Here is my problem: when i readd the event handler on page load it's giving an error cannot cast sender object
I'm using the below to update controls from another thread (works great) How would I call a Sub (Named UpdateList)? The UpdateList updates a listview with a list of databases on a selected SQL instance, requires no arguments.
Private Sub CompleteEventHandler(ByVal sender As Object, ByVal e As Microsoft.SqlServer.Management.Common.ServerMessageEventArgs) SetControlPropertyValue(Label8, "text", e.ToString)
I have found a sample code of something I am trying to complete in VB.Net however the sample is in C++, and I am having a hard time understanding how to translate it.
I have everything basically covered except for the actual EventHandler line.
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I would like to know how to translate this easily into VB.Net. I understand i may have to create an Event and a Raise Event, but not sure how.
Back in form1, how can I wire up the Click event for each MenuItem present in the contextmenu? I want to do this as abstract as possible, meaning I don't want to implement the OnClick code inside Form1.
Code: Public Class Form1 Me.ContextMenu = MenuFactory.BuildMeAContextMenu() End Class
Me.SetProgressBars() AddHandler zip.SaveProgress, New EventHandler(Of SaveProgressEventArgs)(AddressOf Me.zip_SaveProgress) zip.Save(target)
Took some snippets from a MSDN page and molded it into my project ... problem is on every run its setting a value of -1 to something and i cant for the life of me figure out what to!
Private Sub zip_SaveProgress(ByVal sender As Object, ByVal e As SaveProgressEventArgs) Select Case e.EventType Case ZipProgressEventType.Saving_AfterWriteEntry
I have 2 classes that Implement 1 EventHandler. Its part of a fingerprint scanner API but I'm having some issue and I'm not sure if it is my fault in how i use the Implements.Is it ok to have 2 different classes Implement the same EventHandler? Each class then uses the events differently within the class but it almost seems like there is some overlap that is causing some issues. I know this is hard to explain without posting code but since i can pinpoint the problem, idk what to post. My main point is, can you have 2 different classes Implement the same Interface?
I wish to check the hard drive space used in a folder on a hard drive. This will happen continuously as a service, so it will be calculating the space used for thousands of folders all the time. I know that this code can be done easily in dotnet, but it seems to take a really long time. Are there any APIs to do this more efficiently, or does the entire looping process have to occur to do this check?
For me it seems like the an event hooking up on an another event?But I have tried everything to translate this into VB.NET code?I have found out that EventHandler management in VB.NET is far from as good it is in C# as many other things.
How can i cancel the eventhandler, i have a problem with tab browser is that:- i have a set of button image to show the forward and back button which are disable or enable (like IE).Inside my program which are deal with the web_CanGoForwardChanged and web_CanGoBackChanged event.my problem is that if i click on other tab faster than the eventhandler done,i got the wrong image shown on button.how can i stop the eventhandler to prevent the wrong image.
Public Function GetBrowser() As WebBrowser If TabControl1.SelectedTab IsNot Nothing Then For Each c As Control In TabControl1.SelectedTab.Controls If TypeOf (c) Is WebBrowser Then
I'm working on a project that will require me to react to 5 separate events generated by an external device and then do something after a certain delay. The events will normally happen one at a time but may occasionally be simultaneous.
Imports System.Windows.Threading Class MainWindow Private TimerList As List(Of DispatcherTimer)
I am trying to clone some of my Controls, with their EventHandlers. I have a function to retrieve the Delegate of a specific EventHandler.The hard part is to find the correct naming to use.
This is the function I'm using Private Function GetEventDelegate(ByVal ctrl As Control, ByVal eventname As String) As [Delegate]
I am trying to clone some of my Controls, with their EventHandlers. I have a function to retrieve the Delegate of a specific EventHandler.The hard part is to find the correct naming to use.
This is the function I'm using Private Function GetEventDelegate(ByVal ctrl As Control, ByVal eventname As String) As [Delegate]
I'm working on a project that will require me to react to 5 separate events generated by an external device and then do something after a certain delay. The events will normally happen one at a time but may occasionally be simultaneous. Is this a bad idea and if so why?
Imports System.Windows.Threading Class MainWindow Private TimerList As List(Of DispatcherTimer)
I'm having a really weird problem with my current project in Visual Basic 2005.To make a long story short, I have an EventHandler subroutine (Clock1_tick) which triggers on the Elapsed event of a Timer (Clock1). Some, but not all, of the code within the subroutine executes correctly. Some of it doesn't execute at all, even though the debugger shows that each line of code is being read.
The overall details of the program aren't really important, but within the program I have a VB class file which can be instanced via the "New" keyword and contains a series of functions, subroutines, and properties... a typical class file. The class file is for managing sound channels..The frmMain includes a status bar with a label to display the program's current status. It also includes a public sub which recieves a string and sets the text of the status bar:
I have an Unhandled Exception handler that does something like this[code]...
So it looks like from the "add" that the last person that subscribes to Application.ThreadException is the one who gets it (it's not additive as most event handlers are). I don't want to give up my subscription to this eventhandler no matter what. Can anyone think of a way that I could track when I lose my subscription to the Application.ThreadException so I can steal it back from whoever stole it from me?
I'm creating multiple ComboBox and multiple TextBox at runtime and would like for the TextBox BackColor to change when an item in the associated ComboBox is selected. I was able to do this before with a single TextBox and single ComboBox I added during design, but I really don't understand how to tackle this.
In VB.NET, I can't seem to figure out how to do a similar thing.
This doesn't work:
Dim handler As EventHandler = Me.SomeEvent
...due to the following error:
Public Event SomeEvent(sender As Object, e As EventArgs)' is an event, and cannot be called directly. Use a 'RaiseEvent' statement to raise an event.
But this doesn't work either: [Code] So how can I actually get an EventHandler from an event in VB.NET? The only idea that's immediately coming to mind is to use reflection, but that seems pretty ridiculous.
I have a Dialog Box that creates a Link Label for each item in a list.When one of those LinkLabels is clicked the DialogBox raises a LinkClicked event.Before, I was using code like this in the Form that was instantiating the Dialog:[code]But I don't like that for several reasons.What I want to do, and what I thought would be straight forward, was to pass the AddressOf the UserClicked PoLink Method into the ShowClickableLinksDialog Constructor and do an AddHandler within the constructor and also assign the Delegate to a Property on the Dialog so as to RemoveHandler when the Dialog is Disposed.[code]But I get a squiggly on the tempLinkClickedEventHandler after the AddressOf Operator saying: "AddressOf operand must be the name of a method (without parenthesis)"I don't get it.I've played around with a number of permutations and can't get what I feel ought to work, to work.
Ran into this while converting a VB.NET interface to C#; the VB version defines an event which doesn't conform to the typical (object sender, EventArgs e) signature:
I do have a customized treeview which inherits from treeview. The customized treeview offers - amongst other - the functionality to automatically check/uncheck the child and parent nodes according to the selected node.To do so, I use (or mabye abuse?) the AfterCheck-event of the treeview in the class where the inherited treeview is customized. Code looks like that (Submethods not included):
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I temporarily remove the AfterCheck-Event in the event-procedure to avoid it getting fired when I programmatically check/uncheck the checkboxes of the treeview. Works fine so far, only problem I see: if another programmer wants to use the customized tree view and tries to make use of the After-Check-Event, he'll get caught in an infinit loop, because his own After-Check-Event (he added himself to the treeview) was not removed and keeps on firing every time a checkbox is automatically checked/unchecked.
How can I remove ALL methods linked to AfterCheck-Event without knowing which method someone added to the treeview-control? My guess is to use reflection and to get the underlying delegate of the AfterCheck-Event by using the .GetInvocationList somehow - but I was not able to make it work. Feraud
We are developing an application that looks like this: Mainwindow - PaneGroup - Pane
What we want to do is add a handler (AddHandler Pane, AddressOf MethodName) on the mainwindow and throw the event in the Pane. When we want something to change on a collection in the mainwindow, we throw that event in the Pane.
My question is if the pane is removed from the panegroup (doesn't exist anymore), does that handler still live on the mainwindow?
