Class 10 - Using MFC

This class is not fully related to AutoCAD and ObjectARX but it covers an overview of MFC library. This library will allow you to create rich interfaces for your ObjectARX applications easily and with professional style.

Introduction

MFC (Microsoft Foundation Classes) is a powerful library made to allow windows programmers to easily create rich interfaces following the windows standard interface.

The MFC class tree is huge and obviously it is not the objective of this class to make you an MFC wizard. I will present here the main concepts involved when using MFC inside AutoCAD and how to take advantage of its power.

If you would like to use MFC inside your ObjectARX application you will need to link it with MFC libraries which can be done dynamically or statically. Currently ObjectARX only support dynamic linked MFC DLL applications because some of AutoCAD libraries were dynamic linked with MFC and you can't mix static and dynamic linked libraries. To make your application dynamic linked with MFC you need to select MFC Extension DLL option when creating your application.

Resource Management

One of the most important concepts when dealing with MFC libraries is that they are based on resources. Resources are rich information such as bitmaps, icons, string tables, dialog layouts, etc. Each DLL has its own resource package that could be used only by itself or shared with other DLLs (Resource only DLLs for example).

The problem is that your ObjectARX application is running into AutoCAD host application which has its own resources. To solve this problem you should switch the resource context to your DLL, use them, and then switch back to AutoCAD. This can be done manually but there is a couple of classes to help you to easily do that.

The first class, called CAcExtensionModule which will handle your module's own resource and the default resources. To make your application take advantage of this class you will need to create an instance of this class inside each module DllMain() function. This can be done using the following:

AC_IMPLEMENT_EXTENSION_MODULE(theArxDLL);

HINSTANCE _hdllInstance = NULL;

extern "C" int APIENTRY

DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved) {

// Remove this if you use lpReserved
UNREFERENCED_PARAMETER(lpReserved);

if (dwReason == DLL_PROCESS_ATTACH) {

  theArxDLL.AttachInstance(hInstance);

  hdllInstance = hInstance;

}

else if (dwReason == DLL_PROCESS_DETACH) {

  theArxDLL.DetachInstance();

}

return 1;   // ok

}

The second class, called CAcModuleResourceOverride is a handy class that performs the switch from AutoCAD's resource to your application's resource when it is instantiated and then, when it is destroyed, switch back to AutoCAD. To use it, just declare an object of it before using your own resources. When it goes out of scope it will be destroyed and its destructor will switch back. So, this is the way to go:

CAcModuleResourceOverride res;

CMyDialo dlg;

dlg.DoModal();

This way you will successfully create your dialog and won't face strange errors like: "An unsupported operation was attempted". Another possible error happens with other dialog appearing instead of yours! Crazy hum? Remember that this applies to any type of resources including strings placed into string tables.

Using MFC Built-in support

Autodesk has also provided us some great classes to make our application looks like a native AutoCAD feature and work much more integrated with AutoCAD's interface. There are two collections of MFC built-in classes which are grouped by AcUi and AdUi prefixes. The AcUi prefixed classes are made to work inside AutoCAD environment and the AdUi classes are made to work outside AutoCAD but, due to license agreement, could be used only on applications that interact with AutoCAD.

Each of these two classes allow us to create buttons like those one we can see inside AutoCAD native dialogs, allow us to create smart edit controls modified to work with angles, points, texts, etc. There are also great combo boxes that allows us to create Layer like combos, linetype combos, color combos, etc.

These classes really provide you a professional appearance. There are also other advanced features like hack into AutoCAD Options dialog creating your own tab, create dockable dialogs, among many others.

Take a look inside ObjectARX documentation to see a complete list of those classes.