I am still in the process of re-thinking from VB6 to .Net, so please forgive if this is trivial.
In a class I have properties which can change, and when they do they should raise a Changed event.
Public Class CPT
Public Event Changed()
Private gsText As String
Public Property Text() As String
Get
Return gsText
End Get
Set(ByVal sValue As String)
If sValue <> gsText Then
gsText = sValue
RaiseEvent Changed()
End If
End Set
End Property
End Class
Another class features an Add method, in which it adds new items of above class into a collection.
Public Class UFB
Private goTexts As New Dictionary(Of String, CPT)
Public Sub Add(sKey As String, sText As String)
Dim oPT As New CPT
oPT.Text = sText
goTexts.Add(sKey, oPT)
End Sub
End Class
Obviously, UFB objects can not receive Changed events, because oPT is not declared on module level and thus can not feature WithEvents.
What is the .Net way to enable UFB to listen to CPT's Changed events (which appear in many other CPT properties).
Related
Every time i use some class e.g Artikel as follows:
Public Class Artikel
Property ID As Integer
Property Nummer As String
Property Name As String
Property Position As Integer
End Class
For such classes i would like to have collection class. The features i would like to have is like:
--> Add (passing Artikel object)
--> Remove (passing Artikel object)
--> Sort entire collection (based on Position property desc/asc)
--> Compare two Artikels (pass by Artikels and tell by which property has to be compared)
--> Check whether two artikels equals
--> Every added artikel has to be marked by Key (so maybe dictionary)? <key><Artikel>
--> Remove Artikel (passing by Key index)
Could somone from you there tell me or even better provide example of collection class pass those requirments?
EDIT: Startup:
Artikel's collection:
Option Strict On
Public Class Articles
Public Property collection As Dictionary(Of Integer, Artikel)
Sub New()
'Initiate new collection
collection = New Dictionary(Of Integer, Artikel)
End Sub
'Add new Artikel to collection
Public Function AddToCollection(ByVal artikel As Artikel) As Boolean
collection.Add(artikel)
Return True
End Function
'Remove specific Artikel
Public Sub RemoveFromCollectionByArtikel(artikel As Artikel)
If Not IsNothing(collection) Then
collection.Remove(artikel)
End If
End Sub
'Get collection
Public Function GetCollection() As Dictionary(Of Integer, Artikel)
Return collection
End Function
'Sort collection by property position
Public Sub SortByPosition()
collection.Sort()
End Sub
'Remove specific sending keys and then reorder them
Public Sub RemoveAllMarkedAsDeleted(keys As List(Of Integer))
'-- Check whther anything has been marked as deleted
If keys.Count > 0 Then
For Each row In keys
collection.Remove(row)
Next
ReorderKeys()
End If
'Reorder all Artikels in collection
Private Sub ReorderKeys()
Dim newCollection As New Dictionary(Of Integer, Artikel)
Dim index As Integer = 0
For Each collitem In collection
newCollection.Add(index, collitem.Value)
index += 1
Next
collection.Clear()
collection = newCollection
End Sub
End Class
Artikel class (additionally i implemented IComparable to be able to sort)
Option Strict On
Public Class Artikel
Implements IComparable(Of Artikel)
Property ID As Integer
Property Nummer As String
Property Name As String
Property Position As Integer
Public Function CompareTo(pother As Artikel) As Integer Implements IComparable(Of Artikel).CompareTo 'we can sort because of this
Return String.Compare(Me.Position, pother.Position)
End Function
Public Shared Function FindPredicate(ByVal partikel As Artikel) As Predicate(Of Artikel)
Return Function(partikel2 As Artikel) partikel.ID = partikel2.ID
End Function
Public Shared Function FindPredicateByUserId(ByVal partikel As String) As Predicate(Of Artikel)
Return Function(partikel2 As Artikel) partikel = partikel2.ID
End Function
End Class
Parts of it look good, but I would ultimately do it a bit differently. First, consider overloads on the item class to make them easier to create and default initialization:
Public Class Article
Property ID As Integer = -1
Property Key As String = ""
Property Name As String = ""
Property Position As Integer = -1
Property PubDate As DateTime = DateTime.Minimum
Public Sub New()
End Sub
' whatever minimum data a new item requires
Public Sub New(k As String, n As String)
Key = k
Name = n
End Sub
' full initialization:
Public Sub New(k As String, n As String, pos As Int32,
pubDt As DateTime)
...
End Sub
End Class
I added some properties for variety, and I suspect "Nummer" might be the "Key" mentioned in the OP, but whatever it is, I would add it to the Article class as that name, if it has some importance.
You might need a simple ctor for serialization (???). Some of these will find and use a Private parameterless constructor, but your code will be forced to use one of the overloads in order to provide some minimum level of data when a new one is created.
You probably do not need IComparable. That is typically for more complex comparisons, such as multiple or complex properties. An example is a carton or box:
If (width = Other.Width) AndAlso (height = Other.Height) Then
Return 0
ElseIf (width = Other.Height) AndAlso (height = Other.Width) Then
Return 0
End If
Plus more gyrations to work out which is "less" than the other. One reason you dont need it, is because If Art1.Postion > Art2.Postion is trivial. The other reason in your case, is because a Dictionary cannot be sorted.
Rather than a Dictionary, an internal List would work better for some of the things you describe but still allow you to have it act like a Dictionary to the extent you need it to. For this, I might build it using ICollection<T>:
Public Class ArticleCollection
Implements ICollection(Of Article)
Pressing Enter after that line will add all the required methods including:
Public Sub Add(item As Article) Implements ICollection(Of Article).Add
Public Sub Clear() Implements ICollection(Of Article).Clear
Public Function Contains(item As Article) As Boolean Implements ICollection(Of Article).Contains
Public ReadOnly Property Count As Integer Implements ICollection(Of Article).Count
Public Function Remove(item As Article) As Boolean Implements ICollection(Of Article).Remove
It remains completely up to you how these are implemented. It also doesn't rule out adding methods such as RemoveAt(int32) or RemoveByKey(string) depending on what you need/how it will be used. One of the benefits to ICollection(Of T) is that it includes IEnumerable which will allow use for each loops (once you write the Enumerator): For Each art In Articles
To emulate a dictionary to allow only one item with a specific property value:
Public Class ArticleCollection
Implements ICollection(Of Article)
Private mcol As List(Of Article)
...
Public Sub Add(item As Article) Implements ICollection(Of Article).Add
' check for existing key
If KeyExists(item.Key) = False Then
mcol.Add(item)
End If
End Sub
You can also overload them:
' overload to match Article ctor overload
Public Sub Add(key As String, name As String)
If KeyExists(key) = False Then
' let collection create the new item
' with the minimum required info
mcol.Add(New Article(key, name))
End If
End Sub
If you add an Item Property, you can index the collection ( Articles(3) ):
Property Item(ndx As Int32) As Article
Get
If ndx > 0 AndAlso ndx < mcol.Count Then
Return mcol(ndx)
Else
Return Nothing
End If
End Get
Set(value As Article)
If ndx > 0 AndAlso ndx < mcol.Count Then
mcol(ndx) = value
End If
End Set
End Property
' overload for item by key:
Public Property Item(key As String) As Article
An Add method and an Item Property will be important if the collection will display in the standard NET CollectionEditor.
There are several ways to implement sorting. The easiest is to use linq in the code which uses your collection:
Articles = New ArticleCollection
' add Article items
Dim ArticlesByDate = Articles.OrderBy(Function(s) s.PubDate).ToList()
Where PubDate is one of the Article properties I added. The other way to handle sorting is by the collection class returning a new collection (but it is so simple to do, there is little need for it):
Friend Function GetSortedList(bSortAsc As Boolean) As List(Of Article)
If bSortAsc Then
Return mcol.OrderBy(Function(q) q.PubDate).
ThenBy(Function(j) j.Position).ToList()
Else
Return mcol.OrderByDescending(Function(q) q.PubDate).
ThenByDescending(Function(j) j.Position).ToList()
End If
End Function
Whether it implements ICollection(Of T), inherits from ICollection(Of T) or does work off a Dictionary depends entirely on what this is, how it is used and whatever rules and restrictions there are (including if it will be serialized and how). These are not things we know.
MSDN has an article on Guidelines for Collections which is excellent.
Create your class
Public Class Artikel
Property ID As Integer
Property Nummer As String
Property Name As String
Property Position As Integer
sub new (_ID as integer, _Nummer as string, _Name as string, _Position as integer)
ID = _ID
Nummer = _Nummer
Name = _Name
Position = _Position
End Sub
End Class
Create another class which holds a private list and add sub routines to it
Public Class ArtikelList
Private _List as new list (of Artikel)
Public sub remove(Key as integer)
Dim obj as Artikel = nothing
for each x as Artikel in _List
if x.ID = Key then
obj = x
exit for
end if
Next
if not isnothing(obj) then
_List.remove(obj)
end if
End sub
Sub Add(obj as Artikel)
Dim alreadyDeclared as boolean = falsse
for each x as Artikel in _List
if x.ID = obj.id then
alreadyDeclared = true
exit for
end if
Next
if not AlreadyDeclared then
_List.add(obj)
Else
'Somehow inform the user of the duplication if need be.
end if
End sub
End Class
Then use your list class.
dim L as new ArtikelList
L.add(new Artikel(1280, "AFKforever!", "Prof.FluffyButton", 96))
L.remove(1280)
I only added one sub routine as an example. I hope it helps but feel free to ask for more example routines.
This can also be done by creating a class which inherits from the list class, exposing all list class functionality but by using this method you are forced to create every subroutine that will be used. This way you only use routines that you created exclusively for the purpose Artikel objects handling.
Check if two Artikels are equal
Public Class Artikel
Property ID As Integer
Property Nummer As String
Property Name As String
Property Position As Integer
sub new (_ID as integer, _Nummer as string, _Name as string, _Position as integer)
ID = _ID
Nummer = _Nummer
Name = _Name
Position = _Position
End Sub
End Class
Public Overrides Overloads Function Equals(obj As Object) As Boolean
If obj Is Nothing OrElse Not Me.GetType() Is obj.GetType() Then
Return False
else
dim _obj as artikel = obj
if Me.ID = _obj.ID then
Return true
else Return False
End If
End Function
End Class
Use it like:
If x.equals(y) then
'they have the same ID
end if
I had downloaded a C# project and wanted to work on VB.Net so I decided to convert that from C# to VB.NET and I encountered some problems when it came to implementing interfaces. I keep getting errors in VB.NET about implementation about how I must have Read-Only or Write-Only specifiers. I want to get rid of this error but I don't know how I can achieve this.
I have Three Files:
CustomPaintRichText.vb
IUnderlineableSpellingControl.vb
ISpellingControl.vb
The same goes with C#, however in C# it works fine and I want to try to get it to work exactly like that in VB.net.
CustomPaintRichText.vb:
Public Class CustomPaintRichText
Inherits RichTextBox
Implements IUnderlineableSpellingControl
Public m_underlinedSections As Dictionary(Of Integer, Integer)
Public m_protectedSections As Dictionary(Of Integer, Integer)
Public m_ignoredSections As Dictionary(Of Integer, Integer)
Public Property UnderlinedSections() As Dictionary(Of Integer, Integer)
Get
If m_underlinedSections Is Nothing Then
m_underlinedSections = New Dictionary(Of Integer, Integer)()
End If
Return m_underlinedSections
End Get
Set(value As Dictionary(Of Integer, Integer))
m_underlinedSections = value
End Set
End Property
Public WriteOnly Property ProtectedSections() As Dictionary(Of Integer, Integer)
Set(value As Dictionary(Of Integer, Integer))
m_protectedSections = value
End Set
End Property
Public WriteOnly Property IgnoredSections() As Dictionary(Of Integer, Integer)
Set(value As Dictionary(Of Integer, Integer))
m_ignoredSections = value
End Set
End Property
Private spellingEnabled As Boolean
Private spellingAutoEnabled As Boolean
Private m_isPassWordProtected As Boolean
Private penColour As Pen
Public Property WhatPenColour() As Pen
Get
Return penColour
End Get
Set(value As Pen)
penColour = value
End Set
End Property
Public Property IsSpellingEnabled() As Boolean
Get
Return spellingEnabled
End Get
Set(value As Boolean)
spellingEnabled = value
End Set
End Property
Public Property IsSpellingAutoEnabled() As Boolean
Get
Return spellingAutoEnabled
End Get
Set(value As Boolean)
spellingAutoEnabled = value
If Not spellingEnabled Then
spellingEnabled = value
End If
End Set
End Property
Public Property IsPassWordProtected() As Boolean
Get
Return m_isPassWordProtected
End Get
Set(value As Boolean)
m_isPassWordProtected = value
End Set
End Property
End Class
IUnderlineableSpellingControl.vb:
Public Interface IUnderlineableSpellingControl
Inherits ISpellingControl
Inherits IUnderlineable
End Interface
ISpellingControl.vb:
Public Interface ISpellingControl
<Browsable(True)> _
Property IsSpellingEnabled() As Boolean
Property SelectionStart() As Integer
Property SelectionLength() As Integer
Property SelectedText() As String
Property Text() As String
Property ContextMenuStrip() As ContextMenuStrip
Property WhatPenColour() As Pen
Property Parent() As Control
Event Disposed As EventHandler
Event Enter As EventHandler
Event TextChanged As EventHandler
Property [ReadOnly]() As Boolean
ReadOnly Property IsPassWordProtected() As Boolean
Sub Cut()
Sub Copy()
Sub Paste(clipFormat As DataFormats.Format)
Sub [Select](start As Integer, length As Integer)
Function Focus() As Boolean
Sub Invalidate(invalidateChildren As Boolean)
WriteOnly Property IgnoredSections() As Dictionary(Of Integer, Integer)
End Interface
If I keep the cursor carret next to Implements IUnderlineableSpellingControl and hit ENTER key, within the CustomPaintRichText.vb class, I get:
Public Property ContextMenuStrip1 As ContextMenuStrip Implements ISpellingControl.ContextMenuStrip
Public Sub Copy1() Implements ISpellingControl.Copy
End Sub
Public Sub Cut1() Implements ISpellingControl.Cut
End Sub
Public Event Disposed1(sender As Object, e As EventArgs) Implements ISpellingControl.Disposed
Public Event Enter1(sender As Object, e As EventArgs) Implements ISpellingControl.Enter
Public Function Focus1() As Boolean Implements ISpellingControl.Focus
End Function
Public WriteOnly Property IgnoredSections1 As Dictionary(Of Integer, Integer) Implements ISpellingControl.IgnoredSections
Set(value As Dictionary(Of Integer, Integer))
End Set
End Property
Public Sub Invalidate1(invalidateChildren As Boolean) Implements ISpellingControl.Invalidate
End Sub
Public ReadOnly Property IsPassWordProtected1 As Boolean Implements ISpellingControl.IsPassWordProtected
Get
End Get
End Property
Public Property IsSpellingEnabled1 As Boolean Implements ISpellingControl.IsSpellingEnabled
Public Property Parent1 As Control Implements ISpellingControl.Parent
Public Sub Paste1(clipFormat As DataFormats.Format) Implements ISpellingControl.Paste
End Sub
Public Property ReadOnly1 As Boolean Implements ISpellingControl.ReadOnly
Public Sub Select1(start As Integer, length As Integer) Implements ISpellingControl.Select
End Sub
Public Property SelectedText1 As String Implements ISpellingControl.SelectedText
Public Property SelectionLength1 As Integer Implements ISpellingControl.SelectionLength
Public Property SelectionStart1 As Integer Implements ISpellingControl.SelectionStart
Public Property Text1 As String Implements ISpellingControl.Text
Public Event TextChanged1(sender As Object, e As EventArgs) Implements ISpellingControl.TextChanged
Public Property WhatPenColour1 As Pen Implements ISpellingControl.WhatPenColour
Public Sub CustomPaint1() Implements IUnderlineable.CustomPaint
End Sub
Public Property IsSpellingAutoEnabled1 As Boolean Implements IUnderlineable.IsSpellingAutoEnabled
Public Event KeyDown1(sender As Object, e As KeyEventArgs) Implements IUnderlineable.KeyDown
Public WriteOnly Property ProtectedSections1 As Dictionary(Of Integer, Integer) Implements IUnderlineable.ProtectedSections
Set(value As Dictionary(Of Integer, Integer))
End Set
End Property
Public Sub RemoveWordFromUnderliningList1(wordStart As Integer) Implements IUnderlineable.RemoveWordFromUnderliningList
End Sub
Public Event SelectionChanged1(sender As Object, e As EventArgs) Implements IUnderlineable.SelectionChanged
Public Property UnderlinedSections1 As Dictionary(Of Integer, Integer) Implements IUnderlineable.UnderlinedSections
And when I make changes to the CustomPaintRichText from a form, I will have extra additional controls and ultimately nothing works.
The error is in Implements IUnderlineableSpellingControl. It is underlined saying that: 'CustomPaintRichText' must implement 'Event Disposed(sender As Object, e As System.EventArgs)' for interface 'ISpellingControl'. This is one of 30 errors along with the ..must implement..for interface.
Here's the error list if you want to see what kind of errors I'm getting.
Here are the .cs files in case:
CustomPaintRichText.cs
IUnderlineableSpellingControl.cs
ISpellingControl.cs
Congratulations, you made Hans Passant go "Ugh!" :)
Speaking to his point, though, mixing and matching assemblies compiled from VB, C#, C++/CLI, F#, or whatever, is generally encouraged in the .NET world, and is the practical solution to your problem. However, if you insist on transforming this C# project into its VB equivalent, one needs to understand the differences in how interfaces get implemented between these two languages.
C# has two styles of implementation: implicit and explicit (see http://blogs.msdn.com/b/mhop/archive/2006/12/12/implicit-and-explicit-interface-implementations.aspx). VB has only an explicit style, which doesn't work quite the same as C# (see https://msdn.microsoft.com/en-us/library/28e2e18x.aspx).
All of those "must implement" errors mean pretty much what they say: You must use the Implements keyword on the appropriate members of your subclass, because VB doesn't do implicit implementations of interfaces. That's a C# thing. When you hit the ENTER key with the cursor caret next to Implements IUnderlineableSpellingControl, the IDE generated template code for the affected (apparently missing) members, complete with Implements. It did that in trying to be helpful, but in this case you have to look over the code and put in the Implements clauses where they're needed (and probably get rid off that template code).
C# has a neat implicit style where it will automatically "wire-up" implementations by matching member names between your class and the interfaces being implemented. Should there be more than one interface that have the same member (with the same signature), they will all be implemented with the very same member in your class (see http://blogs.msdn.com/b/mhop/archive/2006/12/12/implicit-and-explicit-interface-implementations.aspx). This can be a wonderful or not-so-good thing depending on the situation.
C# has a limited explicit style. One simply defines a member in the named in the format of InterfaceName.MemberName (see https://msdn.microsoft.com/en-us/library/ms173157.aspx).
VB has only its explicit style, but it allows for a list of interface members in the Implements clause so that they all get implemented by the very same member in your class. This is the work-around for C# implicit implementations that hookup multiple interfaces.
Finally, there are some sources which claim that VB cannot do re-implementations of an interface on a subclass of a superclass that already has it implemented (e.g. http://www.dotnetheaven.com/article/how-to-re-implement-interfaces-in-vb.net). I do not know if that was ever true, but I can aver that the VB of VS 2012 and later allows for such re-implementations.
C# allows you to implement a WriteOnly or ReadOnly property with a read/write property. (VB 2015 also allows this).
You can easily work around this prior to VB 2015 - here's an example for your IsPasswordProtected implementation:
Private ReadOnly Property ISpellingControl_IsPassWordProtected() As Boolean Implements ISpellingControl.IsPassWordProtected
Get
Return IsPassWordProtected
End Get
End Property
Public Property IsPassWordProtected() As Boolean
Get
Return isPassWordProtected_Renamed
End Get
Set(ByVal value As Boolean)
isPassWordProtected_Renamed = value
End Set
End Property
The 'Implements' goes on the new ReadOnly property which calls the existing read/write property.
Is there any way to make a class can be only initialized at declaration.
Public Class AnyValue
Private value As Int32
Public Sub New(ByVal aValue As Int32)
value = aValue
End Sub
End Class
'I want to be able to do this:
Dim val As New AnyValue(8)
'But not this.
val = New AnyValue(9)
Or it is possible to stop the assignment or detect when the operator = is used.
Lets just say this - No, you can't do what you want. The closest thing to it that I can think of, is to hide the constructor and give static access to the consumer as follows:
Public Class AnyValue
Private value As Int32
Private Sub New(ByVal aValue As Int32) ' Note - private constructor
value = aValue
End Sub
Public Shared Function Create(ByVal aValue As Int32) As AnyValue
Return New AnyValue(aValue)
End Function
End Class
'This will not work
Dim val As New AnyValue(8)
'This will not work
val = New AnyValue(9)
' This will work
Dim val As AnyValue = AnyValue.Create(8)
Now, if you look at this method of object creation, you can see that you can set all sort of rules for object construction. So, the client has very little input on the construction itself because how you construct the object is totally controlled by the object itself.
I'm having a hard time wrapping my head around some of the answers I've been reading here about unloading a plugin DLL using AppDomains. Here's my architecture:
In my solution, I have a SharedObjects project containing a ModuleBase class that all plugins (separate projects within the solution) inherit. In the SharedObjects project I also have an interface that all plugins implement (so if I have six plugins, they all implement the same interface and therefore the main program using these plugins doesn't need to know or even care what the name of the plugin's class was when it was compiled; they all implement the same interface and therefore expose the same information). Each plugin project has a project reference to the SharedObjects project. (As a side note, may be important, may not be - that SharedObjects project has a project reference to another solution, CompanyObjects containing a number of commonly-used classes, types, objects, etc.) When it's all said and done, when any given plugin compiles, the output directory contains the following DLLs:
The compiled DLL of the plugin itself
The DLL from the SharedObjects project
The DLL from the CompanyObjects project
Four prerequisite 3rd-party DLLs referenced in the CompanyObjects project
My main program creates a reference to the class where I'm doing all my plugin-related work (that class, PluginHelpers, is stored in the SharedObjects project). The program supplies an OpenFileDialog so that the user can choose a DLL file. Now, as it's running right now, I can move just the plugin DLLs to a separate folder and load them using the Assembly.LoadFrom(PathToDLL) statement. They load without error; I check to make sure they're implementing the interface in the SharedObjects project, gather some basic information, and initialize some background work in the plugin DLL itself so that the interface has something to expose. Problem is, I can't upgrade those DLLs without quitting the main program first because as soon as I use LoadFrom those DLLs are locked.
From this MSDN site I found a solution to the problem of locked DLLs. But I'm getting the same "File or dependency not found" error as the OP using the code that worked for the OP. I even get the error when I open the DLL from the release folder which includes the rest of those DLLs.
The FusionLog is even more confusing: there's no mention of the path I was trying to open; it's trying to look in the directory where I'm debugging the main program from, which is a completely different project on a completely different path than the plugins, and the file it's looking for is the name of the DLL but in the folder where the program is running. At this point I have no idea why it's disregarding the path I gave it and looking for the DLL in a completely different folder.
For reference, here's my Loader class and the code I'm using to (try to) load the DLLs:
Private Class Loader
Inherits MarshalByRefObject
Private _assembly As [Assembly]
Public ReadOnly Property TheAssembly As [Assembly]
Get
Return _assembly
End Get
End Property
Public Overrides Function InitializeLifetimeService() As Object
Return Nothing
End Function
Public Sub LoadAssembly(ByVal path As String)
_assembly = Assembly.Load(AssemblyName.GetAssemblyName(path))
End Sub
Public Function GetAssembly(ByVal path As String) As Assembly
Return Assembly.Load(AssemblyName.GetAssemblyName(path)) 'this doesn't throw an error
End Function
End Class
Public Sub Add2(ByVal PathToDll As String)
Dim ad As AppDomain = AppDomain.CreateDomain("TempPluginDomain")
Dim l As Loader = ad.CreateInstanceAndUnwrap(
GetType(Loader).Assembly.FullName,
GetType(Loader).FullName
)
Dim theDll As Assembly = l.GetAssembly(PathToDll) 'error happens here
'there's another way to do it that makes the exact point of the error clear:
'Dim theDll As Assembly = Nothing
'l.LoadAssembly(PathToDll) 'No problems here. The _assembly variable is successfully set
'theDll = l.TheAssembly 'Here's where the error occurs, as soon as you try to read that _assembly variable.
AppDomain.Unload(ad)
End Sub
Can anyone point me in the right direction so I can load and unload DLLs only as-needed and without any dependency errors?
I think I finally got it. It ended up being a few things - I needed the shared DLLs all in one place, and as Hans mentioned above, I needed my appdomains squared away. My solution architecture looks like this: a folder with all my plugin projects; a "Shared Objects" assembly with one class file for the base plugin architecture, and a second class containing my "plugin wrapper" class and supporting classes; and a console app that ties everything together. Each plugin project has a project reference to the shared objects project, as does the console app. Nothing references the plugins directly.
So in my Shared Objects project, I have the code for my PluginBase class and my IPlugin interface:
Public Interface IPlugin
ReadOnly Property Result As Integer
Sub Calculate(ByVal param1 As Integer, ByVal param2 As Integer)
End Interface
Public MustInherit Class PluginBase
Inherits MarshalByRefObject
'None of this is necessary for the example to work, but I know I'll need to use an inherited base class later on so I threw it into the example now.
Protected ReadOnly Property PluginName As String
Get
Return CustomAttributes("AssemblyPluginNameAttribute")
End Get
End Property
Protected ReadOnly Property PluginGUID As String
Get
Return CustomAttributes("AssemblyPluginGUIDAttribute")
End Get
End Property
Protected IsInitialized As Boolean = False
Protected CustomAttributes As Dictionary(Of String, String)
Protected Sub Initialize()
CustomAttributes = New Dictionary(Of String, String)
Dim attribs = Me.GetType.Assembly.GetCustomAttributesData
For Each attrib In attribs
Dim name As String = attrib.Constructor.DeclaringType.Name
Dim value As String
If attrib.ConstructorArguments.Count = 0 Then
value = ""
Else
value = attrib.ConstructorArguments(0).ToString.Replace("""", "")
End If
CustomAttributes.Add(name, value)
Next
IsInitialized = True
End Sub
End Class
<AttributeUsage(AttributeTargets.Assembly)>
Public Class AssemblyPluginNameAttribute
Inherits System.Attribute
Private _name As String
Public Sub New(ByVal value As String)
_name = value
End Sub
Public Overridable ReadOnly Property PluginName As String
Get
Return _name
End Get
End Property
End Class
<AttributeUsage(AttributeTargets.Assembly)>
Public Class AssemblyPluginGUIDAttribute
Inherits System.Attribute
Private _g As String
Public Sub New(ByVal value As String)
_g = value
End Sub
Public Overridable ReadOnly Property PluginGUID As String
Get
Return _g
End Get
End Property
End Class
And I have my PluginWrapper class with its supporting classes:
Imports System.IO
Imports System.Reflection
''' <summary>
''' The wrapper for plugin-related activities.
''' </summary>
''' <remarks>Each wrapper contains: the plugin; code to load and unload it from memory; and the publicly-exposed name and GUID of the plugin.</remarks>
Public Class PluginWrapper
Private _pluginAppDomain As AppDomain = Nothing
Private _isActive As Boolean = False
Private _plugin As IPlugin = Nothing
Private _pluginInfo As PluginInfo = Nothing
Private _pluginPath As String = ""
Public ReadOnly Property IsActive As Boolean
Get
Return _isActive
End Get
End Property
Public ReadOnly Property PluginInterface As IPlugin
Get
Return _plugin
End Get
End Property
Public ReadOnly Property PluginGUID As String
Get
Return _pluginInfo.PluginGUID
End Get
End Property
Public ReadOnly Property PluginName As String
Get
Return _pluginInfo.PluginName
End Get
End Property
Public Sub New(ByVal PathToPlugin As String)
_pluginPath = PathToPlugin
End Sub
Public Sub Load()
Dim l As New PluginLoader(_pluginPath)
_pluginInfo = l.LoadPlugin()
Dim setup As AppDomainSetup = New AppDomainSetup With {.ApplicationBase = System.IO.Directory.GetParent(_pluginPath).FullName}
_pluginAppDomain = AppDomain.CreateDomain(_pluginInfo.PluginName, Nothing, setup)
_plugin = _pluginAppDomain.CreateInstanceAndUnwrap(_pluginInfo.AssemblyName, _pluginInfo.TypeName)
_isActive = True
End Sub
Public Sub Unload()
If _isActive Then
AppDomain.Unload(_pluginAppDomain)
_plugin = Nothing
_pluginAppDomain = Nothing
_isActive = False
End If
End Sub
End Class
<Serializable()>
Public NotInheritable Class PluginInfo
Private _assemblyname As String
Public ReadOnly Property AssemblyName
Get
Return _assemblyname
End Get
End Property
Private _typename As String
Public ReadOnly Property TypeName
Get
Return _typename
End Get
End Property
Private _pluginname As String
Public ReadOnly Property PluginName As String
Get
Return _pluginname
End Get
End Property
Private _pluginguid As String
Public ReadOnly Property PluginGUID As String
Get
Return _pluginguid
End Get
End Property
Public Sub New(ByVal AssemblyName As String, ByVal TypeName As String, ByVal PluginName As String, ByVal PluginGUID As String)
_assemblyname = AssemblyName
_typename = TypeName
_pluginname = PluginName
_pluginguid = PluginGUID
End Sub
End Class
Public NotInheritable Class PluginLoader
Inherits MarshalByRefObject
Private _pluginBaseType As Type = Nothing
Private _pathToPlugin As String = ""
Public Sub New()
End Sub
Public Sub New(ByVal PathToPlugin As String)
_pathToPlugin = PathToPlugin
Dim ioAssemblyFile As String = Path.GetFullPath(Path.Combine(Path.GetDirectoryName(_pathToPlugin), GetType(PluginBase).Assembly.GetName.Name) & ".dll")
Dim ioAssembly As Assembly = Assembly.LoadFrom(ioAssemblyFile)
_pluginBaseType = ioAssembly.GetType(GetType(PluginBase).FullName)
End Sub
Public Function LoadPlugin() As PluginInfo
Dim domain As AppDomain = Nothing
Try
domain = AppDomain.CreateDomain("Discovery")
Dim loader As PluginLoader = domain.CreateInstanceAndUnwrap(GetType(PluginLoader).Assembly.FullName, GetType(PluginLoader).FullName)
Return loader.Load(_pathToPlugin)
Finally
If Not IsNothing(domain) Then
AppDomain.Unload(domain)
End If
End Try
End Function
Private Function Load(ByVal PathToPlugin As String) As PluginInfo
Dim r As PluginInfo = Nothing
Try
Dim objAssembly As Assembly = Assembly.LoadFrom(PathToPlugin)
For Each objType As Type In objAssembly.GetTypes
If Not ((objType.Attributes And TypeAttributes.Abstract) = TypeAttributes.Abstract) Then
If Not objType.GetInterface("SharedObjects.IPlugin") Is Nothing Then
Dim attribs = objAssembly.GetCustomAttributes(False)
Dim pluginGuid As String = ""
Dim pluginName As String = ""
For Each attrib In attribs
Dim name As String = attrib.GetType.ToString
If name = "SharedObjects.AssemblyPluginGUIDAttribute" Then
pluginGuid = CType(attrib, AssemblyPluginGUIDAttribute).PluginGUID.ToString
ElseIf name = "SharedObjects.AssemblyPluginNameAttribute" Then
pluginName = CType(attrib, AssemblyPluginNameAttribute).PluginName.ToString
End If
If (Not pluginGuid = "") And (Not pluginName = "") Then
Exit For
End If
Next
r = New PluginInfo(objAssembly.FullName, objType.FullName, pluginName, pluginGuid)
End If
End If
Next
Catch f As FileNotFoundException
Throw f
Catch ex As Exception
'ignore non-valid dlls
End Try
Return r
End Function
End Class
Finally, each plugin project looks a little like this:
Imports SharedObjects
<Assembly: AssemblyPluginName("Addition Plugin")>
<Assembly: AssemblyPluginGUID("{4EC46939-BD74-4665-A46A-C99133D8B2D2}")>
Public Class Plugin_Addition
Inherits SharedObjects.PluginBase
Implements SharedObjects.IPlugin
Private _result As Integer
#Region "Implemented"
Public Sub Calculate(ByVal param1 As Integer, ByVal param2 As Integer) Implements SharedObjects.IPlugin.Calculate
If Not IsInitialized Then
MyBase.Initialize()
End If
_result = param1 + param2
End Sub
Public ReadOnly Property Result As Integer Implements SharedObjects.IPlugin.Result
Get
Return _result
End Get
End Property
#End Region
End Class
To set it all up, the main program creates a new instance of the PluginWrapper class, supplies a path to a DLL, and loads it:
Dim additionPlugin As New PluginWrapper("C:\path\to\Plugins\Plugin_Addition.dll")
additionPlugin.Load()
Once you're done doing whatever you need to do with the program...
additionPlugin.PluginInterface.Calculate(3, 2)
...and retrieving the results...
Console.WriteLine("3 + 2 = {0}", additionPlugin.PluginInterface.Result)
...just unload the plugin:
additionPlugin.Unload()
If you need to reload it while the wrapper is still in memory, just call the Load() method again - all the information it needs to create a new AppDomain and reload the assembly is in there. And, in answer to my initial question, once the Unload() method has been called, the assembly is freed and can be replaced/upgraded as necessary, which was the whole point of doing this in the first place.
Part of where I was getting tripped up earlier was that I wasn't including the SharedObjects.dll file in the same folder as the plugins. What I found is that any referenced assembly needs to be present. So in my post-build events for both my plugins and the Shared Objects project, I have this: xcopy /y $(ProjectDir)$(OutDir)$(TargetFileName) c:\path\to\Plugins. Every time I build the solution, all the DLLs are placed in the folder where they need to be.
Sorry if this is a little long, but this is a little complicated. Maybe there's a shorter way to do it...but at the moment, this gets me everything I need.
The code below works for the class that I hard coded "XCCustomers" in my RetrieveIDandName method where I use CType. However, I would like to be able to pass in various classes and property names to get the integer and string LIST returned. For example, in my code below, I would like to also pass in "XCEmployees" to my RetrieveIDandName method. I feel so close... I was hoping someone knew how to use CType where I can pass in the class name as a string variable.
Note, all the other examples I have seen and tried fail because we are using Option Strict On which disallows late binding. That is why I need to use CType.
I also studied the "Activator.CreateInstance" code examples to try to get the class reference instance by string name but I was unable to get CType to work with that.
When I use obj.GetType.Name or obj.GetType.FullName in place of the "XCCustomers" in CType(obj, XCCustomers)(i)
I get the error "Type 'obj.GetType.Name' is not defined" or "Type 'obj.GetType.FullName' is not defined"
Thanks for your help.
Rick
'+++++++++++++++++++++++++++++++
Imports DataLaasXC.Business
Imports DataLaasXC.Utilities
Public Class ucCustomerList
'Here is the calling method:
Public Sub CallingSub()
Dim customerList As New XCCustomers()
Dim customerIdAndName As New List(Of XCCustomer) = RetrieveIDandName(customerList, "CustomerId", " CustomerName")
'This code below fails because I had to hard code “XCCustomer” in the “Dim item...” section of my RetrieveEmployeesIDandName method.
Dim employeeList As New XCEmployees()
Dim employeeIdAndName As New List(Of XCEmployee) = RetrieveIDandName(employeeList, "EmployeeId", " EmployeeName")
'doing stuff here...
End Sub
'Here is the method where I would like to use the class name string when I use CType:
Private Function RetrieveIDandName(ByVal obj As Object, ByVal idPropName As String, ByVal namePropName As String) As List(Of IntStringPair)
Dim selectedItems As List(Of IntStringPair) = New List(Of IntStringPair)
Dim fullyQualifiedClassName As String = obj.GetType.FullName
Dim count As Integer = CInt(obj.GetType().GetProperty("Count").GetValue(obj, Nothing))
If (count > 0) Then
For i As Integer = 0 To count - 1
'Rather than hard coding “XCCustomer” below, I want to use something like “obj.GetType.Name”???
Dim Item As IntStringPair = New IntStringPair(CInt(CType(obj, XCCustomers)(i).GetType().GetProperty("CustomerId").GetValue(CType(obj, XCCustomers)(i), Nothing)), _
CStr(CType(obj, XCCustomers)(i).GetType().GetProperty("CustomerName").GetValue(CType(obj, XCCustomers)(i), Nothing)))
selectedItems.Add(Item)
Next
End If
Return selectedItems
End Function
End Class
'+++++++++++++++++++++++++++++++
' Below are the supporting classes if you need to see what else is happening:
Namespace DataLaasXC.Utilities
Public Class IntStringPair
Public Sub New(ByVal _Key As Integer, ByVal _Value As String)
Value = _Value
Key = _Key
End Sub
Public Property Value As String
Public Property Key As Integer
End Class
End Namespace
'+++++++++++++++++++++++++++++++
Namespace DataLaasXC.Business
Public Class XCCustomer
Public Property CustomerId As Integer
Public Property CustomerName As String
End Class
End Namespace
'+++++++++++++++++++++++++++++++
Namespace DataLaasXC.Business
Public Class XCCustomers
Inherits List(Of XCCustomer)
Public Sub New()
PopulateCustomersFromDatabase()
End Sub
Public Sub New(ByVal GetEmpty As Boolean)
End Sub
End Class
End Namespace
'+++++++++++++++++++++++++++++++
Namespace DataLaasXC.Business
Public Class XCEmployee
Public Property EmployeeId As Integer
Public Property EmployeeName As String
End Class
End Namespace
'+++++++++++++++++++++++++++++++
Namespace DataLaasXC.Business
Public Class XCEmployees
Inherits List(Of XCEmployee)
Public Sub New()
PopulateEmployeesFromDatabase()
End Sub
Public Sub New(ByVal GetEmpty As Boolean)
End Sub
End Class
End Namespace
From MSDN
CType(expression, typename)
. . .
typename : Any expression that is legal
within an As clause in a Dim
statement, that is, the name of any
data type, object, structure, class,
or interface.
This is basically saying you can't use CType dynamically, just statically. i.e. At the point where the code is compiled the compiler needs to know what typename is going to be.
You can't change this at runtime.
Hope this helps.
Since List(Of T) implements the non-generic IList interface, you could change your function declaration to:
Private Function RetrieveIDandName(ByVal obj As System.Collections.IList, ByVal idPropName As String, ByVal namePropName As String) As List(Of IntStringPair)
And then your troublesome line would become (with also using the property name parameters):
Dim Item As IntStringPair = New IntStringPair(CInt(obj(i).GetType().GetProperty(idPropName).GetValue(obj(i), Nothing)), _
CStr(obj(i).GetType().GetProperty(namePropName).GetValue(obj(i), Nothing)))
Of course, you could still have the first parameter by Object, and then attempt to cast to IList, but that's up to you.
ctype is used to convert in object type.