Licensing ActiveX Controls

Licensing an ActiveX control consists of providing a license key at design-time and supporting the creation of licenses dynamically for controls created at runtime.

To provide design-time licenses, a key is created for the control , which is stored in a file with the same name as the project with the LIC extension. This .LIC file is added to the project. The user of the control must have a copy of the .LIC file to open the control in a development environment. Each control in the project that has Make Control Licensed checked has a separate key entry in the .LIC file.

To support runtime licenses, the wrapper class implements two methods, GetLicenseString and GetLicenseFilename. These return the license string for the control and the name of the .LIC file, respectively. When a host application tries to create the ActiveX control, the class factory for the control calls these methods and compares the string returned by GetLicenseString with the string stored in the .LIC file.

Runtime licenses for the Internet Explorer require an extra level of indirection because users can view HTML source code for any Web page, and because an ActiveX control is copied to the user's computer before it is displayed. To create runtime licenses for controls used in Internet Explorer, you must first generate a license package file (LPK file) and embed this file in the HTML page that contains the control. The LPK file is essentially an array of ActiveX control CLSIDs and license keys.

Note: To generate the LPK file, use the utility, LPK_TOOL.EXE, which you can download from the Microsoft Web site (www.microsoft.com).

To embed the LPK file in a Web page, use the HTML objects, <OBJECT> and <PARAM> as follows:

Copy Code

<OBJECT CLASSID="clsid:6980CB99-f75D-84cf-B254-55CA55A69452">
<PARAM NAME="LPKPath" VALUE="ctrllic.lpk">
</OBJECT>

The CLSID identifies the object as a license package and PARAM specifies the relative location of the license package file with respect to the HTML page.

When Internet Explorer tries to display the Web page containing the control, it parses the LPK file, extracts the license key, and if the license key matches the control's license (returned by GetLicenseString), it renders the control on the page. If more than one LPK is included in a Web page, Internet Explorer ignores all but the first.

For more information, look for Licensing ActiveX Controls on the Microsoft Web site.

What do you think about this topic? Send feedback!