Visual Basic 6.0 allows you to dynamically load ActiveX controls when an
application is running. Some ActiveX controls require the use of a license
in order for them to be used within a program. The Licenses Collection of
an application contains the license information for all loaded ActiveX
controls and allows you to add and remove these Licenses as needed.
This article demonstrates how to create an ActiveX Control that requires a
license and how to load that control dynamically.
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ActiveX controls used within a Visual Basic 6.0 application may require a
license. During development, you can add references to controls within your
project and use these controls as you would use intrinsic Visual Basic
controls. At compile-time, Visual Basic will incorporate the license for a
control into the EXE, so the control can be used in that application on
other machines without needing the license on that machine.
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Steps to Create an ActiveX Control
| 1. | Create a New ActiveX Control project in Visual Basic.
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| 2. | Add a Label to the control, and set the label's caption to "Test
Control."
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| 3. | Select Project1 Properties from the Project menu.
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| 4. | On the "General" tab, check "Require License Key." This will ensure a
design-time license is required for using this control.
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| 5. | Add the following code to the UserControl1 object:
Private Sub UserControl_Initialize()
UserControl.BackColor = vbBlue
End Sub1
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| 6. | Save the project and make the .OCX.
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NOTE: The ProgId (Programmatic Identifier) of the ActiveX control will be
Project1.Usercontrol1. ProgIds will be discussed in more detail later in
this article.
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Steps to Create a Test Client for the License Control
| 1. | Create a new Standard EXE project in Visual Basic. Form1 will be
created by default.
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| 2. | Add two CommandButtons to Form1.
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| 3. | Add the following code to Form1:
Option Explicit
' create an object reference so a control can be dynamically loaded
' during run-time.
Private ctlMyTestControl As VBControlExtender
Private Sub Command1_Click()
' The test control will be loaded without its design-time license
' first. This will result in an error that will be trapped or
' reported in a MSGBOX.
On Error GoTo NoLicense
' load the test control dynamically.
Set ctlMyTestControl = Form1.Controls.Add("Project1.UserControl1", _
"ctlTest")
' show the test control.
ctlMyTestControl.Visible = True
' exit this function.
Exit Sub
NoLicense:
' make sure the error is about the license for this control.
If Err.Number = 731 Then
MsgBox "You need a License to dynamically load this ActiveX" & _
& " control"
End If
End Sub
Private Sub Command2_Click()
' add the license of the test ActiveX control to the
' running application and then dynamically load the
' control.
Licenses.Add "Project1.usercontrol1"
' load the test control dynamically.
Set ctlMyTestControl = Form1.Controls.Add("Project1.UserControl1", _
"ctlTest")
' show the test control.
ctlMyTestControl.Visible = True
End Sub
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| 4. | Press the F5 key to run the project.
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| 5. | Press the "Command1" button. This will load the ActiveX UserControl
without loading its design-time license. You will receive an error
message.
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| 6. | Press the "Command2" button. This will load the ActiveX UserControls
license and then dynamically load the control and display it on the
form.
|
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Caveats About ActiveX Control and Licenses
| • | ActiveX controls referenced within a Visual Basic project do not need to
have their licenses loaded before dynamically loading them. They are
already included within the Licenses Collection and trying to add a
license twice will result in a trappable run-time error.
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| • | Simply copying and registering a Visual Basic ActiveX UserControl onto a
target machine does not mean the license will be installed. You need to
distribute the ActiveX control through the Package and Deployment Wizard
and have the end user install the control before the ActiveX control can
be dynamically loaded during run-time.
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| • | Trying to add a license to the License Collection of an ActiveX control
that does not need one will result in a trappable run-time error.
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| • | The Licenses Collection has two properties for each item; a LicenseKey
and a ProgId. The LicenseKey item is encrypted so the actual license
for an ActiveX control is not revealed to either the developer or the
end user.
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| • | It is common to reference a control during development and forget to
remove its reference before compiling and distributing the end
application. Select the "Remove Information About Unused ActiveX
Controls" from the Project Properties Make Tab to remove references to
UserControls that you might have added during development time, but are
only used dynamically at runtime. This will ensure that the license
information for unused controls are not included within the EXE.
|
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ProgIds for ActiveX Controls
In order to load an ActiveX control Dynamically, you need to know the
ProgId of the control. If the control was developed by you in Visual Basic
6.0, the ProgId will follow the PROJECTNAME.CONTROLNAME convention.
To learn the ProgId for an ActiveX control, add a reference to the control
to a project. Use the Object Browser (F2) to see all the object models
available.
If you are going to load an ActiveX control at run-time and perform license
checking, make sure you remove the reference to the control from the
project, or select the "Remove Information About Unused Active Controls"
option mentioned above.
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