A Plugin Architecture In .net And Handling Events
Nov 5, 2009
I need to write an app that that will iterate over our database, and perform various anaylsis on each record. In order to do this (partially for the learning exercise in creating plugin support) I want to use a Plugin model.
Currently, I have a simple Interface in my main app, which plugins can Implement. My app then loads all DLL's in a folder looking for ones implementing the Interface.
As you can see in the pseudo-code below, I have to keep performing a loop through all loaded plugins calling the process methods.
Sub ProcessData()
For Each Record In MyDataSet
For Each Plugin In MyPluginCollection
[Code].....
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Jun 22, 2010
how to create a stable plugin architecture. Stable because I plan on opening up plugin creation to the public but I dont want a sloppy coded plugin to take down my whole application.
So I thought of using an AppDomain per plugin and I did a little seaching. But it seems that even using a temp AppDomain to load plugins and then unloading it once all assemblies have been inspected raises complexity allot and I was planing on using an AppDomain per plugin.
I feel the gained stability (if there is any at all) may be raising the complexity so much the app will never be done..
Is there another way to both create a stable application and at the same time making it extensible?
I cases where the host calls a defined function via say IPluginInterface I guess I can pack a whole lot of try catch blocks around that call but what if a plugin insisted of a timed routine that would run continously without being invoked from the host other that a starting call to StartPluginService or something like that?
If I include a plugin like that in the default AppDomain and it blows up I sure will blow my own foot off right?
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Jan 25, 2010
I'm experimenting with a plugin architecture for my company's internal business system. I have managed to read all .DLLs in a Plugin folder which implement a specific interface. What I am trying to figure out is the best method of communication between the "host" MDI parent application and forms that will be in the .DLLs which I intend to make MDI children.
Currently, I am returning just ToolStripMenuItem objects from the .DLLs to add to the MDI Parent. I've also tested that events wired in the .DLLs to the ToolStripMenuItems do propagate to the code in the .DLLs. I've also managed to return a Form object via the interface and open that form, as the Plugin folder is being "scanned".
However, I am not clear how I would make these forms MDI children. Also, any other forms living in the .DLLs will also have to be MDI children. I created a VS 2008 Addin project just to see what's going on, and it seems that the Addin accepts an Application object on which it adds to the ToolStripMenuItems and does other operations. The code to build the menu inside the .DLL. This is opposite of what I have done so far, where the MDI requests a ToolStripMenuItem from each .DLL and adds the returned object to its own menu.
Would designing my plugin architecture to accept an application object in the same manner the only way I could get forms to open as an MDI child? Am I asking for other, currently unknown to me, headaches by NOT passing in the application object to the .DLL?
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Apr 17, 2012
Here's my current set-up:
Public Interface IDatabase
Function CreateParameter(name as String, dbType as <dbTypeEnumeration>)
End Interface
[Code]....
The problem here is what exactly is dbTypeEnumeration. In the example above, it's simply a placeholder to what my problem is. Since we use both Oracle and SQL Server databases, the DbTypes are different depending on the database being used. For Oracle, the OracleClient object has its own OracleDbType enumeration with types. SQL Server also has its own enumeration.
My question is: is it possible to show those database-specific enumerations depending on which repository is injected into the DatabaseService constructor? If not, what's the best way to go about this? I want to separate the two databases, share logic, and allow for future development, ala the interface as a code contract for that development.
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Sep 20, 2010
ve been exploring with IThumbnailProvider in VB10. The first attempt I made was to handle MKV file thumbnails. I made the library and everything looked OK when I tested it against MS's Thumbnail app that came in the Windows API pack. Then I attempted to implement it on my computer, and every single thumbnail in the OS broke. Not a single thumbnail was generated by the system. So, after a bunch of trying to rescue thumbnails, I reformatted, reinstalled Windows, and got everything back to normal.
Today, I tried again. This time, using BLP files which are often used in Blizzard games (Warcraft III in particular). To avoid the same issue, I threw the compiled result into a Virtual Machine and tested it there, and it looked lovely. After a bit of experimenting and tweaking, I got it exactly as I wanted, cleaned the thumbnail cache, tested it one last time, and then installed it on my actual PC. Bam, all thumbnail generation is broken again.
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Jun 30, 2009
I am working on an application with plugins. I have created the plugin host and the plugin, now I need to figure out how to pass data back to the main application from the plugin. IE: I have MainApp that has plugins in a subfolder. It loads the plugins and shows a menu item the launches the plugin. When the plugin launches it opens a windows form inside the plugin. The form does some calculations and then returns data in a string array. How do I pass that string array back to the main application?
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Jun 7, 2009
I'm calling the SQLDMO 8.0 COM library from VB.NET (using a PIA I generated with tlbimp) in order to backup a database with percentage completion notification:
Dim server As SQLDMO.SQLServer = Nothing
Dim backup As SQLDMO.Backup = Nothing
Dim restore As SQLDMO.Restore = Nothing
Dim backupAbortable As Boolean
Dim restoreAbortable As Boolean
[Code]...
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Jan 22, 2009
I have a component written in C# which exposes an event which the clients can Handle. I would like know how to handle this event in VB.Net?
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May 12, 2009
I have some VB6 code that instantiates a class which handles events that are being raised from a VB.NET component. The VB6 is pretty straightforward:private m_eventHandler as new Collection
public sub InitSomething()
dim handler as EventHandler
set handler = new EventHandler
m_eventHandler.Add handler
m_engine.Start
[Code]...
My problem is that when I debug the VB6 program, the first time InitSomething gets called, the event will not be handled (the VB6 event handler is never entered). Subsequent calls to InitSomething does work.
Everything works as I would have expected when I run the program outside the debugger. At this point, I'm not even sure if this is something I should be worried about.It may or may not be relevant but the VB.NET was converted from a VB6 using the Visual Studio code conversion tool (and subsequently manually cleaned up).
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Nov 8, 2009
Work = New ExampleWork()Here the Work is a withevents variable and I've used the handles clause for handling various events fired by the ExampleWork object. However the event handler will not get assigned till the constructor of the ExampleWork returns. Now how can I handle any events fired from the constructor? I can move the constructor logic out to a separate method and call it after the constructor has returned and thus handle all the fired events including events fired from constructor. However it doesn't look good
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Feb 12, 2012
Handling Events For An Array Of Controls
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Nov 23, 2011
I took a VB class a couple semesters ago and I did really well. Unfortunately, it seems as though we only covered the very basics within the class, as I feel rather clueless right now.
Here's my issue. I'm trying to write a program that will encode notes (like music notes, A-G#) which are entered by the user, into digits, 0-9. Now I have the system laid out, in that 1-8 will represent A-A, while a 0 or 9 preceding a digit will represent a flat or sharp respectively.
Now my question is actually rather basic, but I just can't seem to figure out how to do this. The user will enter the note sequence by clicking on buttons (12 of them). What I'd like to do is create one sub that will handle all possible button clicks. I suppose it's possible that I could have separate subs for each and every button; but it just seems more efficient and cleaner to have one sub that manages them all.
The part I have completed and working properly will display a message (the same message) in a messagebox each time any of the buttons are clicked. So I have the "Handles" part working for all 12 buttons. But what I'd like to do is write code, perhaps "If" statements such that If "btnA" is clicked, then say "You clicked Button A," and If "btnASharp" is clicked, then "You clicked Button A Sharp," and so on. Is it possible to do this somehow by recognizing which event was actually triggered?
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Jan 28, 2012
I am trying to make a UserControl or Component which can be dragged from the Toolbox onto a container control such as a Form or a Panel. Its purpose is to change the behaviour of that container. In particular, I would like to add functions to the container's painting and mouse actions. I DO NOT want to have to write code for the container itself -- that's the whole point of the Toolbox object.
I can do this by getting a reference to the object's Parent (or Host in the case of a Component) and handling its events, as this example illustrates:
[Code]...
However, I have heard that handling the events of a parent control conflicts with OOP principles. So I would like to know, does that objection apply in a case like my example? If so, what are the drawbacks? And what alternative techniques are available?
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Apr 14, 2011
I am creating a program using Visual Basic 2010 Express.
I want to make a Sub handling both MouseHover and MouseLeave events. Is this possible? And if possible, how do I differ between MouseHover event and MouseLeave event?
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May 7, 2009
I would like to use MS Office automation and have event handlers that fire for user-triggered events. For example, if the user clicks the save button in Word, I want to intercept that event and execute code in my program.
I don't want to be bound to a specific version of Word because I don't know what version my user will be running, so I instantiate a reference to Word using late binding. The problem is that the AddHandler and the Dim WithEvents commands require specific references to an object that is known at design time. Given this, how can I define an event handler without having an early bound reference to a specific version of the Word library?
I can try to a reference to an earlier version of Word with the expectation that newer versions of Word will be backwards compatible, but this seems kludgey and risky.
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Aug 1, 2011
Assuming I have the following repeater.
[Code]...
But this has failed (The event is never raised)..
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Dec 3, 2010
I had a question about handling multiple events in a sub, like this:
Private Sub Form1_MouseUpOrDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseUp, Me.MouseDown
'do something
End Sub
Once the sub is called, is there any way to tell which event called it? (Whether it was a MouseDown or a MouseUp event?) Right now, I am doing a work-around as follows... having each event call the same sub and pass the info in. But it would be nice to not have that overhead.
Private Sub Form1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
ExecuteMouseUpOrDown(EventTypes.MouseDown, sender, e)
End Sub
[CODE]...
Don't use ACCESS, EXCEL, or a TEXT FILE as a database. If you want your program to use a "local database", without any of the hassle of setting up a MS SQL or MySQL server, just click this link: >>> SQLite <<<.
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Aug 10, 2010
I have multiple textboxes which I want them to perform the same thing upon clicking them. By default I can use the handles textbox1.click for 1 single textbox as shown below but I am not sure how to do handle multiples of them. Of course I can write a handler for every single textbox but I have about 50 of them. I am sure there must be a more efficient way. [Code]
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Mar 22, 2010
In order to take advantage of the spell checking ability of WPF textboxes, I have added one to a user control (with the use of elementhost). This user control is used in various window forms. My current problem is trying to handle keyup events from this textbox but the windows form is unable to "get" any event from the control. I can access the properties of the textbox just fine (i.e. text, length, etc.) but keyboard events don't seem to work.I have found, however, that the following will bring back events from the WPF textbox:
Public Class MyUserControl
Private _elementHost As New ElementHost
Private _wpfTextbox As New System.Windows.Controls.Textbox
[code].....
The user control is now able to do something after the PreviewKeyUp event is fired in the WPF textbox. Now, I'm not completely sure how to have the window form containing this user control to work with this.
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Oct 21, 2009
I am new to VB but I want to find this out. For example there are two objects in my form and when I press W,A,S,D then Object1 should move Up, Left, Down and Right respectively. Object2 moves when I press the arrow keys. How do I make them move together and also separately depending on whether the key is pressed.
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Aug 5, 2010
Whenever we need to handle events, we do it by creating a method which handles the event. Without creating methods; is there some other ways of handling events?
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Jan 24, 2009
I am trying to create a ContextMenuStrip where I add a certain amount of ToolStripMenuItems based on how many columns are in a DataGridView via code. I am wondering, since I am creating all these ToolStripMenuItems in code, how would I handle the "CheckStateChanged" event on all of them separately? Or how can I figure out which one of those ToolStripMenuItems was clicked?
Here's a code example of what I mean:
Private Sub CreateCMS()
Dim CMS As New ContextMenuStrip
Dim TMS_Main As New ToolStripMenuItem
[Code].....
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Jul 24, 2009
[2005] Handling Events With ToolStripMenuItems Created With Code
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Jul 18, 2009
I'm writing a tabbed web browser for someone who is learning VB.NET, and I have got to the point where I can add/remove browser controls into tab pages, controlled by one set of buttons on the main form, but I can't handle events from the WebBrowser objects.I have tried this but it says that 'DocumentTitleChanged' isnt an event of 'Control'...
Dim browser As New ArrayList
browser.Add(New WebBrowser)
browser(0).parent = TabControl1.SelectedTab
browser(0).dock = DockStyle.Fill
AddHandler browser(0).DocumentTitleChanged, TitleChangedHandler()
I want to update the tab title with the web page title when it changes. I started using a timer to update the tabs but there must be a way to add an event handler here.
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Apr 26, 2010
come years ago I bought an activex component to read some basic smartcard data. I created a simple form application and it has worked fine ever since. However, instate of a form application I now want to create a console application for the same purpose (the forms are unrequired and it just takes too long with multiple smartcards).
But I have been working on this for days now and somehow can't seem to get my events working. When I use 1 event, everything works fine, but as soon as I add my second event I get this error:
Unhandled Exception: System.Runtime.InteropServices.COMException (0x80040202): E
xception from HRESULT: 0x80040202
at System.Runtime.InteropServices.ComTypes.IConnectionPoint.Advise(Object pUn
kSink, Int32& pdwCookie)
[Code]...
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Apr 4, 2012
the question is really what is the correct convention (style) for raising and handling events. When a button is clicked it is generally handled by this method. [Code]
I have recently been trying to follow this convention by creating my own EventArgs class and inheriting the system.eventargs, Then adding my own properties. The problem is as my projects get bigger/complex I seem to be writing multiple eventarg classes. I then decide to try and create a generic eventarg class but this then seemed pointless thinking it would be easier just to pass the object directly instead of wrapping it up in "someEventArg" i have created.
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May 19, 2012
I have various input textboxes on my form. And based on entries made in each of the input textboxes, I update the display textbox. However, using AppendText message of textbox. I have my input textboxes set to accept only numeric values. So for each character inputted correctly, I update the display Textbox. Problem I have is when user selects Key.Back or Key.Delete, what I would like to do is do a Delete of last character in the display textbox, but I am yet to get this right. How do I delete the last character in the string that is contained in a TextBox using AppendText()
[Code]...
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Sep 8, 2009
I have an object, say Order where if an error occurs, it raises the ErrorOccurred event. If I'm running some code in say, the codebehind for a .aspx page with an public Order registered as WithEvents and I want to check to see if an error has occurred before I run more code, how do I do this? I can't simply check theOrder.ErrorOccurred. Do I have to create a local boolean flag that switches over in the event handler (OnErrorOccurred)?
Example:
Public WithEvents theOrder As New Order
Public Sub DoStuff()
theOrder.DoSomething()
If theOrder.ErrorOccurred Then
[code]....
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Nov 6, 2009
I was wondering does anyone know where i can find some good books and or articles covering the architecture and design of OOP applications. Also I need a book that explains how to structure an application as it relates to the data tier, business logic tier, and the front end.
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Jun 3, 2009
In the first comment (by J.W.) to this question: Using ObjectDataSource and DataObjectTypeName, How Do You Handle Delete Methods With Just An Id Parameter?, it is said that using ObjectDataSource is a bad design. What is considered good design for well-architected ASP.NET applications?
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