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Managing the License for an ActiveX Control in Visual Basic 6

Many ActiveX controls cannot be freely distributed to end users but instead require a license before the system will allow them to be used in applications.

VB will raise a runtime error if an ActiveX control requires a license key and you attempt to add an instance of that ActiveX control to the Controls Collection without providing the license key (see Figure 4.19).

A runtime error caused by the lack of a license key for an ActiveX control added to the Controls Collection.
FIGURE 4.19 A runtime error caused by the lack of a license key for an ActiveX control added to the Controls Collection.

To provide a license key to the runtime environment, you must determine the contents of the key and then add the key to the Licenses Collection before trying to add an instance of the control to the Controls Collection. Add the key to the Licenses collection with a call to its Add method using the following syntax:

Licenses.Add Controltype, LicenseKey

where ControlType is the string representing the control's ProgID and LicenseKey is the string representing the license key for that type of control.

So how do you find out the license key for a particular control type? In your development environment, you can make a call to Licenses.Add that automatically adds the control's License key to the Licenses Collection without having to know the License key beforehand, and at the same time provides the license key in a string that you can examine. The syntax for such a call would be:

StrLicenseKey = Licenses.Add(ControlType)

where strLicenseKey is a string variable that will hold the license key for the control type. When you run this line in your development environment, you can then examine the contents of strLicenseKey (using a Debug.Print message or some other display technique) to find out the contents of the license key for that control type.

When you release your product to end users, you can change your code to the first syntactic format listed above to allow your application to load the control on the user's workstation. You would hardcode the key that you discovered as the second argument to the Licenses.Add method.

Adding and Deleting Controls Dynamically Using the Controls Collection Topics

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