How to Use QT to write DLL programs in Windows

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How to Use QT to write DLL programs in Windows

Because QT must call the exec method of qapplication to generate a message loop and the QT program can run. Therefore, if we use QT to write a DLL program, it cannot be called in common Windows programs. An error occurs during the call. Of course, QT provides a solution: qtwinmigrate

Here is an introduction to qtwinmigrate on the official QT Website:

Http://qt.nokia.com/products/appdev/add-on-products/catalog/4/Windows/qtwinmigrate

The following describes how to use qtwinmigrate to compile a DLL.

First, we need to rewrite the dllmain function:

# Include <qtwinmigrate/qmfcapp. h> <br/> # include <qtwinmigrate/qwinwidget. h> <br/> # include <qmessagebox. h> <br/> # include <windows. h> <br/> bool winapi dllmain (hinstance, DWORD dwreason, lpvoid lpvreserved) <br/>{< br/> static bool ownapplication = false; <br/> If (dwreason = dll_process_attach) <br/> ownapplication = qmfcapp: plugininstance (hinstance); <br/> If (dwreason = dll_process_detach & ownapplication) <br/> Delete qapp; <br/> return true; <br/>}</P> <p>

We all know that the dllmain function is the entry function of the Windows dynamic library. If you use the qt ui in the DLL, you must first create a global qapplication and the application must create an eventloop.

Go to the qmfcapp: plugininstance method,

Bool qmfcapp: plugininstance (QT: handle plugin) <br/>{< br/> If (qapp) <br/> return false; <br/> qt_wa ({<br/> hhook = setwindowshookexw (wh_getmessage, qtfilterproc, 0, getcurrentthreadid (); <br/> }, {<br/> hhook = setwindowshookexa (wh_getmessage, qtfilterproc, 0, getcurrentthreadid (); <br/>}); <br/> int argc = 0; <br/> (void) New qapplication (argc, 0); <br/> If (plugin) {<br/> char filename [256]; <br/> If (getmodulefilenamea (hinstance) Plugin in, filename, 255) <br/> loadlibrarya (filename ); <br/>}</P> <p> return true; <br/>}< br/>

 

We can see that the qapplication is created. Qmfcapp: plugininstanc is used to ensure that a qapplication object exists in the process, and the DLL needs to load the qapplication instance to the memory.

Below are the export functions in dll:

Extern "C" _ declspec (dllexport) bool showdialog (hwnd parent) <br/>{< br/> qwinwidget win (parent); <br/> win. showcentered (); <br/> qmessagebox: About (& Win, "about qtmfc", "qtmfc version 1.0/ncopyright (c) 2003 "); </P> <p> return true; <br/>}< br/>

The export function in dll must be in the form of extern "C", and qwinwidget provides a stack for the Native WIN32 window.

 

The program has not been written. No. You can use this program.

Qmake-Project

Qmake

Nmake

In this way, it cannot be compiled in any way.

If you carefully read the examples of qtwinmigrate, you will notice:

Include (D:/qt4.4.3/qtwinmigrate-2.8-opensource/src/qtwinmigrate. PRI)

 

You must add this sentence to the *. Pro file during compilation! Remember, remember!

 

Reference: http://doc.trolltech.com/solutions/qtwinmigrate/winmigrate-qt-dll-example.html