ATL Window Classes

Introduction

In the late 1980s, Windows development was a really difficult task. Working in the Windows development environment meant only learning the Windows API. Everything in your Windows source code had to be accurate; otherwise, your program would not run. And above all, every Windows application was similar in one or the other way.

That’s why MFC came into existence. It saves developers from rewriting the message loops and window procedures. The catch is it was purely automatic. The developer does not have the choice to change or manipulate anything as per the situation’s requirements.

The ATL Window Classes is a reasonable mediator between adding MFC and coding straight from scratch.

This blog will teach various aspects of ATL Window Classes and several types of ATL Window Classes.

ATL stands for Active Template Library. It is a library with numerous classes that permit you to use, manipulate and implement Windows. It provides an impressive implementation that would not cause overhead on your code.

ATL includes a set of template-based C++ classes that simplify the programming of Component Object Model (COM) objects. COM is a necessary specification used in creating and consuming software components on Windows. It is highly recommended when you want to use ATL Window Classes to their fullest extent. Some of the prominent COM features include dual interfaces, stock implementations, connection points, standard COM enumerator interfaces, ActiveX controls, and tear-off controls.

The diagram below shows the hierarchy of an ATL Window Class.

The table below describes several commonly used ATL Window Classes shown in the hierarchy.

ATL Class	Description
CWindow	This class allows you to attach a window handle to the CWindow object. You can use CWindow methods to manipulate any window.
CWindowImpl	It implements a completely new window and processes messages using a message map. You can create a window based on an existing window class, and a superclass or subclass of an existing class.
CDialogImpl	This class permits you to implement a modeled or modeless dialog box and process messages using a message map.
CContainedWindowT	It is a prebuilt class used to implement a window whose message map is already present in another class. It permits you to centralize message processing in just one class.
CAxDialogImpl	This class permits you to implement a modeled or modeless dialog box that hosts ActiveX controls.
CSimpleDialog	This class implements a dialog box with a few basic functionalities.
CAxWindow	It allows you to implement a Window that hosts an ActiveX control.
CAxWindow2T	It allows the implementation of a Window that hosts a licensed ActiveX control.
CWndClassInfo	This class manages the information of a new Window Class.
CWinTraits	It provides a simple way for standardizing the traits of an ATL Window Object.
CWinTraitsOR	This class is the same as ‘CWinTraits’ class. However, it is compulsory to define some traits while using this class.

We are done with learning the types of ATL Window Classes. Now, we will have a look at how to use a Window.

Using a Window

We use CWindow class to use any window. You have to attach that window to a CWindow object and call the CWindow methods to use and manipulate the Windows. You can easily merge CWindow method calls and Win32 function calls without creating or using any temporary objects.

There is an operator called ‘HWND operator’ in the CWindow class to convert a CWindow object into HWND. This way you can pass any CWindow object to desired function that needs a handle to a window. However, the HWND member is automatically passed to the corresponding Win32 function if using the CWindow class. Also, some other CWindow methods wrap the corresponding Win32 API functions along.

You already know that any ATL Window class does not cause an overhead on your code, and so does the CWindow class. This is because it has only two data members- a window handle and some default dimensions.

In addition, you can derive data or code from any class and add it to the CWindow class directly to use it anyway further. The ATL library derives three other ATL Window Classes from the CWindow class- CWindowImpl, CDialogImpl, and CContainedWindowT.

Frequently Asked Questions

Mention some uses of Windows.

Windows allows its users to view and store files, run the software, watch videos, play games, watch videos, and facilitate connection with the Internet.

Which Window’s version is the latest?

Windows 11, the successor to Windows 10, is the latest version of the Windows Operating System.

Give some advantages of the Sliding Window Protocol.

Sliding Window Protocol allows users to send frames even if the receiver is comparatively slow at processing frames. That means you can send multiple frames at once.

Mention a few disadvantages of the Sliding Window Protocol.

The sequence numbers are not bound to be in the range, and extra bandwidth usage can be a serious issue. This leads to some extra costs.

Conclusion

On the whole, we understood the aspects of ATL Window Classes. We also learned various types of ATL Window Classes.

We hope the above discussion helped you understand the concepts of ATL Window Classes and can be used for reference whenever needed. To learn more about Windows, you can refer to blogs on the Windows Operating System, Features of the Windows Operating System, Windows Forms, JavaScript Window, and Sliding Window Protocol.

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Happy Coding!