Sorry, you don't exec(), that's why. You just need to create a QApplication (or derived class). For the UI to work, there just has to be a QApplication running somewhere. In a standard Qt application, you'd call need to call exec() to start the message loop, but in a plugin there's already a message loop in Illustrator. So long as a QApplication exists, when you call exec() on something like a dialog, it'll work.

I have developed a GUI in Qt as a "Qt GUI Application' in which I have created a QWidget. The UI design (both static and dynamic) is ready in this QtCreator's project. This project has a ".ui" file, which the QtCreator translates to a ".h" during compile time. I want to use this UI for my plugin. My plugin interface is a panel. Can I make the QtProject as library project which includes all required Qt libraries within and use this library in my plugin ? Or is there any other way to keep the UI (may be a static lib) and the plugin (.aip = dll) be kept totally separate.

We use the generated project as our plugin, so yes, you can do this. We find it much easier this way. If you read the qmake documentation, you can find out how to change the extension of the plugin to .aip and (I think its the same configuration option) control the output destination (makes debugging easier).

You could also have this generate a static lib if you wanted probably, but its up to you.

Also, sAiPanel->GetPlatformWindow() will give me the HWND for windows. How can I embed the QWidget on this panel ?? Basically what I am searching a way to use the cababilities of QtCreator + visual studio both to generated a Qt based panel plugin for Ai . And now I have no idea of either. Please help me get started.

I reccommend you use either Visual Studio or QtCreator and not both. Either is probably fine. We use Visual Studio, but maybe Creator is better, I don't know (don't have much experience there).

As for using the .ui you created, you'll find some good examples in the documentation, but it basically boils down to this:

Create a class like this:

#include "ui_name_of_ui_file.h" // this is generated when you compile a .ui file

class CMyDialog : public Ui::name_class_in_ui_file {

CMyDialog() { setupUi(this); }

}

setupUi(this) basically creates all the widgets, etc. so that all the members you're inheriting from your ui class actually exist. After that, it's just like any other class. If it's a dialog, call exec() to show it, and start implementing all your dialog functionality.

Adding it to a panel is a little trickier. On Windows, look for QWinWidget. I believe you create a QWinWidget and give it the result of GetPlatformWindow. This basically creates a QWidget that represents the handle you pass it, so that widget is now the panel frame. You'd then parent your panel widget (defined in the .ui file) off of that QWinWidget and it *should* be in your panel in Illlustrator. Lots of little details after that (you'll probably want to connect resizing the panel to resizing your widget, etc.) but that's the gist.