.net - Understanding AddHandler And Pass Delegates And Events
Mar 17, 2010
I am using AddHandler to wire a function to a control's event that I dynamically create:
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This code is generating a run-time exception stating: Unable to cast object of type 'MyEventHandlerDelegate' to type 'System.EventHandler' What am I not understanding about System.Delegate even though AddHandler takes as an argument of type "System.Delegate"? What Type does "EventHandler need to be to cast to a type that AddHandler can accept?
What is the difference b/w Delegates and Events. I have little bit confusion. Where delegates are used, and when we have to used delegates. Can, you give some examples(both delebates and events) in vb.net.
I have a number of UserControls that have the same event .
When I use an Object instead of UserControl, I can not use Addhandler.
Here is the simplest example of my problem: In this example error is "TextChanged is not an event of Object"
Dim obj As Object = TextBox1 AddHandler obj.TextChanged, AddressOf text_changed_event I have to use this structure, because in a FOR loop I use some different UserControls as obj. All UserControls have the same event.
Is there a way to use this structure without error?
Maybe there is a way to define a new object that covers all my UserControls.
I have a number of UserControls that have the same event .When I use an Object instead of UserControl, I can not use Addhandler.Here is the simplest example of my problem:In this example error is "TextChanged is not an event of Object"
Dim obj As Object = TextBox1 AddHandler obj.TextChanged, AddressOf text_changed_event I have to use this structure, because in a FOR loop I use some different UserControls as
I am hoping there is a way to do this.I have a base class that has event handling in it. My console application is running my workflow. Part of that workflow is to raise events at specific intervals in a separate thread to broadcast the workers' current state (a heartbeat I have heard many call it).
I also have another program in the same solution that is a windows form that I want it to be able to listen to what is going on in the console application so that it can display the worker states. I have tried running both at the same time and verified the events are triggering, but the monitor is not finding any of the raised events.
I am fearing that there is no way to do this, and I will need to go to a database logging method or something else... but in the off chance someone knew how to communicate between applications with event (or event-style) logic, I would appreciate it.Currently the applications are running from the same location. The goal is that the monitor application will eventually be attached with a broadcaster for our network so that our workstations can monitor for certain worker states without being logged into the machine and the main monitor will show us the full status of all the workers.
I have ended up with the following event structure in a custom control - it seemed to be the recommended way for my scenario in MSDN (though it wasn't easy to follow!) This is the MSDN page I used,MSDN - How to: Implement Events in Your Class.
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What now has me totally confused (even more so than I was about setting up the above pattern) is what to declare in the Interface? I wanted to declare the event in the interface since there will be several other classes that do similar things and they need to be used interchangeably (hence an Interface in the first place) and if I've gone down the Interface route it seems smart to make sure the 'minimum' content that each class will have to implement declared in the Interface...
Can we pass parameters to a function using delegates
Private Sub UpdateLabel(byval text as string) If Me.Label1.InvokeRequired Then Me.Label1.Invoke(New MethodInvoker(AddressOf UpdateLabel)) Else Label1.Text = text
I am in the process of prototyping a small sockets application, which monitors IT infrastructure (due to in-house financial and deployment restrictions, I am unable to utilise an existing commercial or open-source solution). Basically, I have a server application and associated agent process for communicating heart-beat data to the server. The server application implements a TCP socket class (TCPDevice), which is called from a WinForm. I am aware of the restriction on updating the UI from processes running on separate threads, and that the preferred technique for acheiving this is via the use of Delegates in conjunction with the Invoke method. Having had very little need previously for using Delegates (apart from of course std windows events and the BackGroundWorker control), I am at a loss as to how to do this in the context of my application, and would appreciate some assistance, although it has occurred to me that I could use the backgroundworker for marshalling updates to the UI.
Eventually the application will need to update a grid of devices via feeds from the defined agents, however for the purpose of this exercise simply updating a status bar on the UI will suffice. The section of the code which I believe is relevant to propogating the code to the form is contained in the OnDataReceived method.Below is a code excerpt from the protoype app which should put the above into appropriate context:
I'm using VS2008, vb.net, and winforms. I've got 3 comboboxes on the same form who are all bound to the same data. If an item is added in one, I want the change reflected in the other two. I'm trying to create one sub to handle the adding of an item for all three combos. I found that the "sender" object appears to contain the control name. The Sub I created is not working quite right because after the item is added, the combo list display repeats itself. So instead of "Item1, Item2, Item3" after adding "Item3", I get "Item1", "Item2", "Item1", "Item2", "Item3". This coding works fine if I were to copy it to the Key_Down event for each combo and reference it directly (for example, use cboSpecialty1.Items.[code]...
I have 3 click events in my form. I have delcared a string variable called sVariable in the following format: Public sVariable As String but when I try to use the value from the sVariable variable then it does not pass the value to the other click events. so in the Button1_Click event i type the following
I am trying to put a new face on an old C program. The C program is, of course, unmanaged code, designed smartly to separate the number crunching and the interface, and the interface I'm trying to replace is X windowing. The graphics part is where it gets a little hairy, because the C is going to need to continue to draw in my new interface, based on the data the program produces. Even if I want to duplicate that data in .NET so that the .NET side can handle all of the drawing, the fact remains I'm going to need to operate on the graphics window in some fashion from C.
I gather that handles have a lot to do with the bare Win32 graphic operations. Is such a similar handle provided to, say, a PictureBox element in .NET? And if so, is it the kind of handle I can use in the unmanaged code without an issue?
I have tried and tried and tried to google for the solution for weeks now, and all I come up with are either C++ solutions (using object-oriented GDI+) or some sort of extension to the C language.
Alternatively, is there a way I can have .NET create a handle specifically for this purpose of having C draw it?
To sum it up, I am using Visual Basic .NET 2008 and a C DLL (also compiled in VS2008), so far in the little testing I've done, I've been able to marshal complex structures to and fro, but I am not sure how exactly I'd let C do any drawing on the .NET form, if that was even possible.
I am writing an application that has to read and interpret data stored in some PDF files. The reading part is done but I am only able to get a dump of all the words on a page and not the format of the words. What I mean is that if I have to extract a table, I am getting the numbers in the table but not the markup which defines the table.
Further, there is some formatting used which displays a few of these numbers within parentheses (meaning that those numbers are negative) but the parentheses themselves are not part of the text. Hence, I am not able to distinguish between positive and negative numbers present in the PDF table!
How do you get the PDF markup along with the text? Is a PDF similar in structure to an XML with tags used to markup tables etc.? If not, then, is there a resource which describes the salient features of the PDF DOM? I am using VBA and the Acrobat library (AcroExch etc.)
I am trying to use my first predicate and I generate the error:Method 'Public Function FindIndex(list As MyProgram.HTMLFiles) As Boolean' does not have the same signature as delegate 'Delegate Function Predicate(Of T)(obj As String) As Boolean'.[code]
I have this RichTextbox in my vb.net form and I would like to when a user click a button, for example to embold the selected text, how would I do this.Also, I do NOT want to use the standard vb.net expressions such as RichTextBox1.SelectedText.Font.Bold = true. I want to do something like RichTextbox1.SelectedRTF="[bold]" & RichTextBox1.SelectedRTF & "[/bold]" or whatever RTF looks like.Can I just add the RTF options random places or can a RichTextBox return an error if the text is in wrong format. I'm mostly looking for info on how to work with RTF without using the standard vb expressions.
My goal is to read a data streaming from a machine the streaming is divided in tre main parts,the first is a 10 byte array that declare the length of the second and third part.The second one, the header, is a 22 DWORD (*32bit) ( 88 byte ) structured of mixed data types.I can easly read the value inside this header when the DWORD contains just one information using something like: [code] My problem starts because some of these DWORD contains several indipendent informations, for example DWORD #4 [ channel 2 peaks 31..16] [channel 1 peaks 15..0].For what I understood the first 16 bits ( so 2 bytes) are used to store the information of the first channel , while the second 16 bits are used for the second channel, I tryed converting the first 2 byte with System.BitConverter.ToUInt16()but without success.Can someone explain me what to do and how these numbers are supposed to be stored?
so i have a class called FOOTBALL,then another 3 classes/forms that inherit FOOTBALL, they control score (SCOREBOX), possession (POSSBOX), and quarter (QUARTERBOX).the FOOTBALL class has 4 variables, "score" (array of 2 ints), "teams" (array of 2 strings), "possession" (boolean), and "quarter" (int)after that i have another form called MAINBOX, which creates new instances of the 3 classes (SCOREBOX, POSSBOX, and QUARTERBOX) (like this: private scoring = new SCOREBOX)... however they all technically create their own FOOTBALL classes, so I cannot connect them.
I started out with VB.NET but now mostly do C#. I never really got to grips with events in VB. I'm trying to translate an old VB.NET program (from 2002) into C#. I've dealt with everything apart from statements such as these:
Public Event UpgradeProgress(ByVal strProgressString As String, _ ByVal strCurrentFile As String, ByVal intProgressPercent As Integer, _ ByVal lngTimeRemaining As Long, ByRef blnCancel As Boolean)
It is my understanding that in .Net 4.0, VB will have an in-memory compiler.
I have to admit I don't know a lot about the compilers so I'm trying to understand the advantage of this as compared to what we had before this. Also, will C# be coming out with the same type of compiler?
I'm confused on the results of this code. The results extracts the tag "div" but why isn't the results containing the word "Yoga"? Shouldn't the result have only one element because it should exit the for loop after finding the first element? The results show hundreds of elements
Dim ElementCollection2 As HtmlElementCollection = WebBrowser1.Document.GetElementsByTagName("div") For Each curElement As HtmlElement In ElementCollection2
I wanted to know what the main areas are and what the array is actually doing in the code. I know that dim is declaring the variables, but how do i exactly explain this code line by line.
PS: the areas in red are the main areas im trying to understand annotate.
Public Class Form1 Private Sub Label1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label1.Click End Sub
If i have a class called A and a class called B, if B inherits A that means A is the super class and B is the subclass. I have been asked to describe why class A is not an abstract class but as i see it class A is an abstract class A, as it has been created for Class B to use in the future, is it something to do with Class B not being able to access the fields in Class A as although they are private by default?
As far as I understand from the docs, it seems that Application.Run() starts a message loop on the current thread, which in turns enables it to process user input (Is that right?).The overloaded version Application.Run(Form) basically does the same, only it exists when the form closes, and it shows the form by default.timer ticks after 20mns, and has to execute say approx. 15 tasks one by one, every time creating an instance of a progress dialog, initially hidden in the taskbar.
Looking at the following code snippet in VS2008 (this is from the SBS book)
Dim HumanAge As Integer = 0 If HumanAge <> 0 And 7 / HumanAge <= 1 Then MsgBox("1 dog year or older")[code]....
I expect to get a runtime error, because And evaluates both conditions, which is why in this case AndAlso should be the better operator to use. When I try this code there is no difference in behavior between 'And' & 'AndAlso'. In neither case I get a runtime error, not even when I flip the conditions around. Is this by design, a lucky accident, or do I just not get it?
UPDATE: See the bottom of this question for what I did to solve the problem.I'm trying to understand how the ItemsSource and DataContext properties work in a Silverlight Toolkit DataGrid. I'm currently working with dummy data and trying to get the data in the DataGrid to update when the value of a combo box changes.
I have a situation in a program I'm writing where I'm not sure of the best way of coding a couple of objects and was hoping for a few pointers.I am using VB.NET 2003, so F/wrk v1.1. My business is horticultural in nature and I'm trying to help streamline the business with a new order fulfillment app.In my program, I have products. Some products don't have any component parts, but others are made up of a selection of plants.For example: we sell a trowel, which obviously doesn't have any component parts. But we also sell a large vegetable garden, which is made up of, say, 20 rocket plants, 30 salad plants, 5 spring onions, etc.[code]I believe the ProductContents table is technically referred to as a 'join table'?
I have written the classes in VB.NET which load, save, edit the Products and the Plants. I also have Manager classes which store collections of these objects (ProductMgr, PlantMgr).I have dealt with situations before with join tables where there are only two columns which are both FKs and both make up a composite PK (ie - to express a one-to-many relationship). This is pretty straightforward (using my product/plant tables as an example) because when I load an individual Product from the database, I also run a second SELECT query which returns any PlantIDs associated with that PlantID from ProductContents. I store that in an array of integers within the Product object. I can then load Plants from the PlantMgr object based on the PlantIDs stored in this array. I kind-of do the reverse when I save the Product to the database, I run a second INSERT query which updates the ProductContents table with the Plants associated with the Product.Where I'm getting stuck is with the inclusion of the extra 'Quantity' column. I can no longer store the PlantIDs in an array of Integers because I also need to store the Quantity associated with that Plant. I also can't use the PlantMgr object any more (to express which Plants are in each Product) because it also doesn't include any information about Quantity.I was just wondering if there is a standard way of handling this kind of situation, where I have a 'join table' which also includes extra columns as well as the two columns that identify the join.
I'm trying to figure out why the following VB.Net code seems unable to upload a file to my ISP's FTP server, since it doesn't report any error but I'm not getting the notification e-mail I'm supposed to receive once a file has been uploaded.So I launched the free Fiddler proxy on 127.0.0.1:7777, but it doesn't report any activity, even with its "Capture FTP Requests" option checked:[code]Is there a way to watch the FTP session to understand why the file seems to be uploaded successfully but I'm getting no success notification?
a member mentioned, xml is similar to a txt file. txt files, i can manipulate quite well. so, if this is the case, it should not be to complicated to do as the thread title describes . that, of course is, if you already know how to even create an xml file. i do not. any and all input/suggestions welcomed, links for xml noobing welcomed as well.
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