The point of the tip is about gaining access to the design time form from within a property editor (
UITypeEditor) in Visual Studio using Visual Basic.
I was creating a Visual Studio property editor (
UITypeEditor) for a .Net
component that holds a subset of the
controls on the
form to which it is attached at design time. Initially I had great difficulty working out how to do that but as usual, once you discover the answer, it turns out to be pretty easy.
The image below shows a demo application using the custom
UITypeEditor. There's a custom component with a property, called
TargetControls, which uses that custom
UITypeEditor. The actual property editor itself is the form bottom left (red border) and as you can see it contains a list of the
controls on the form shown at the top. The image is from within Visual Studio, not in debugging mode, so that's the form designer you can see at the top.
It's pretty easy to create a
Collection(Of Control) at run-time, where the
Controls in the
Collection are the
Controls on the
Form. It's notably more difficult to do this at design time - and that's what I needed to do, so I created a
UITypeEditor that can populate a
Control property with one or more of the
Controls on a form at design time. I used the Creating Property Editors in DesignTime for VS.Net Easily (UITypeEditor Helper) article by S.Serpooshan to provide the base class.
Here I will reproduce only the part of the code for retrieving the list of Controls on the form since the full class will (hopefully) be the subject of an article rather than a tip.
Using The Code
UITypeEditor there is a method called
EditValue, whose job is to display the custom control (a dropdown or a modal form) and update the property dependent on how the user interacts with the control. I've removed all the surrounding code that loads and shows the custom control and the code that manages updating the property in order to focus the tip on the interesting bit. All the other stuff you can get from S.Serpooshan's article.
myControl is a reference to the custom property editor control, which in this case is a form with a
CheckedListBox (the name of which is
For Each loop adds items to that
CheckedListBox having accessed a reference to the design time form through the
context paramater of the
EditValue function. Working out that this parameter gives you a way to reference the design time form was the key, it's pretty easy from there.
For Each loop simply determines which items in the
CheckedListBox to check before displaying it, i.e. those that are held in the current value of the property before the user gets chance to edit it.
Public Overrides Function EditValue(ByVal context As ITypeDescriptorContext, ByVal provider As IServiceProvider, ByVal value As Object) As Object
For Each c As Component In context.Container.Components
If TypeOf c Is Control Then
If value IsNot Nothing Then
Dim tCollection As Collection(Of Control) = CType(value, Collection(Of Control))
Dim found As Integer
For Each c As Control In tCollection
found = myControl.AvailableControls.Items.IndexOf(c)
If Not found = -1 Then
To use the code you would create a custom component with a public property of type
Collection(Of Control). You'd then set its
EditorAttribute to the class name of the
Public Class ControlCollectionUITypeEditor
Public Class ExampleComponent
Private _TargetControls As New Collection(Of Control)
Public Property TargetControls As Collection(Of Control)
Set(ByVal value As Collection(Of Control))
_TargetControls = value
Points of Interest
I went around the houses on this with a couple of folk at the MSDN Visual Basic General forum, the main thrust of which is 'you can't do it'.
You can if you try hard enough!
Version 1: Original Tip