ActiveX Controls and Control Hosting

ATL is still the best way to implement ActiveX controls, and you don't need to change anything to get your ATL 3 ActiveX controls to compile under ATL 8. In addition, the ActiveX control-hosting support has been improved significantly in ATL 8.

Readers of the previous edition of this book might remember that the chapters on ActiveX controls and control hosting spent several pages describing bugs in ATL 3, and the code downloads included functions and classes to work around these errors. I'm very happy to report that somebody at Microsoft apparently read a copy of ATL Internalsmost of those bugs have been fixed.

Stock properties now provide a callback function that you can override to detect when the stock property is changed. This means that you no longer have to completely replace the put_XXXX stock property methods that the CStockPropImpl base class provides.

The AtlIPersistPropertyBag_Load method has been fixed, so you no longer need the updated function included with the first edition downloads.

The ActiveX hosting classes have been significantly cleaned up. The first edition of this book included a class named CAxWindow2 that fixed several memory leaks in the control hosting. These leaks have now been fixed. ATL 8 also includes a class named CAxWindow2; luckily, it's a drop-in replacement for the ATL Internals class of the same name, so all you need to do is remove the patched version from your project. ATL 8 ActiveX Hosting also now supports the creation of licensed ActiveX controls. The new CAxWindow2 class provides the support for creating licensed controls, but it works just fine for nonlicensed controls as well.

Take a look at Chapters 11, "ActiveX Controls," and 12, "Control Containment," in this edition for the full scoop on ActiveX controls.