Widgets must be created in the GUI thread.

**mvuori** · 3rd July 2011, 19:05

Originally Posted by ThÃ nh ViÃªn Má»›i

hi all, i dont understand why my program error Widgets must be created in the GUI thread.

it use Qthread loop WaitForSingleObject(hEvent, INFINITE);

I don't understand either, but I do not see any reference to WaitForSingleObject in the C++ source.

**ChrisW67** · 4th July 2011, 00:37

Run you project in your debugger. When is asserts look back through the backtrace of the non-main thread(s) until you find the line in your code that is causing the problem.

**ThÃ nh ViÃªn Má»›i** · 4th July 2011, 15:33

Originally Posted by mvuori

I don't understand either, but I do not see any reference to WaitForSingleObject in the C++ source.

no, haven't you read my source code attach ???

Qt Code:

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#include "threadwaitforaddgroupevent.h"
 
ThreadWaitForAddGroupEvent::ThreadWaitForAddGroupEvent()
{
    hEvent = CreateEventA(NULL, FALSE, FALSE, EVENT_ADD_NEW_GROUP);
    hMapFile = CreateFileMappingA(
                    INVALID_HANDLE_VALUE,    // use paging file
                    NULL,                    // default security
                    PAGE_READWRITE,          // read/write access
                    0,                       // max. object size
                    BUF_SIZE,                // buffer size
                    MAP_FILE_ADD_NEW_GROUP);                 // name of mapping object
    if (hMapFile == NULL)
    {
            return ;
    }
}
 
void ThreadWaitForAddGroupEvent::ProcessDataFromMapFile()
{
    HANDLE hMapFile = OpenFileMappingA(
                    FILE_MAP_ALL_ACCESS,   // read/write access
                    FALSE,                 // do not inherit the name
                    MAP_FILE_ADD_NEW_GROUP);               // name of mapping object
    if (hMapFile == NULL)
    {
            return ;
    }
    char *pBuf = (char*) MapViewOfFile(
            hMapFile,              // handle to map object
            FILE_MAP_ALL_ACCESS,   // read/write permission
            0,
            0,
            BUF_SIZE);
 
    if (pBuf == NULL)
    {
            return ;
    }
    QString dataFromMapFile(pBuf);
    QList<QString> lUserNewGroup = dataFromMapFile.split('|');
    emit AddNewGroup(lUserNewGroup);
 
}
 
void ThreadWaitForAddGroupEvent::run(){
    while(1){
        WaitForSingleObject(hEvent, INFINITE);
        ProcessDataFromMapFile();
    }
}
 
ThreadWaitForAddGroupEvent::~ThreadWaitForAddGroupEvent(){
    UnmapViewOfFile(pBuf);
    CloseHandle(hMapFile);
}

#include "threadwaitforaddgroupevent.h"

ThreadWaitForAddGroupEvent::ThreadWaitForAddGroupEvent()
{
    hEvent = CreateEventA(NULL, FALSE, FALSE, EVENT_ADD_NEW_GROUP);
    hMapFile = CreateFileMappingA(
                    INVALID_HANDLE_VALUE,    // use paging file
                    NULL,                    // default security
                    PAGE_READWRITE,          // read/write access
                    0,                       // max. object size
                    BUF_SIZE,                // buffer size
                    MAP_FILE_ADD_NEW_GROUP);                 // name of mapping object
    if (hMapFile == NULL)
    {
            return ;
    }
}

void ThreadWaitForAddGroupEvent::ProcessDataFromMapFile()
{
    HANDLE hMapFile = OpenFileMappingA(
                    FILE_MAP_ALL_ACCESS,   // read/write access
                    FALSE,                 // do not inherit the name
                    MAP_FILE_ADD_NEW_GROUP);               // name of mapping object
    if (hMapFile == NULL)
    {
            return ;
    }
    char *pBuf = (char*) MapViewOfFile(
            hMapFile,              // handle to map object
            FILE_MAP_ALL_ACCESS,   // read/write permission
            0,
            0,
            BUF_SIZE);

    if (pBuf == NULL)
    {
            return ;
    }
    QString dataFromMapFile(pBuf);
    QList<QString> lUserNewGroup = dataFromMapFile.split('|');
    emit AddNewGroup(lUserNewGroup);

}

void ThreadWaitForAddGroupEvent::run(){
    while(1){
        WaitForSingleObject(hEvent, INFINITE);
        ProcessDataFromMapFile();
    }
}

ThreadWaitForAddGroupEvent::~ThreadWaitForAddGroupEvent(){
    UnmapViewOfFile(pBuf);
    CloseHandle(hMapFile);
}

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SendEvent:

Qt Code:

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#include <QtCore/QCoreApplication>
#include <QtGui/QMessageBox>
#include <QString>
#include <windows.h>
 
#define BUF_SIZE  1024
#define MAP_FILE_ADD_NEW_GROUP  "Local\\MyFileMappingAddNewGroup"
#define EVENT_ADD_NEW_GROUP     "Local\\eventaddnewgroup"
 
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    HANDLE hMapFile;
    char* pBuf;
 
    QString qstrDataSend = "ADDKJHGFDSDFGHJ";
    hMapFile = OpenFileMappingA(
                            FILE_MAP_ALL_ACCESS,   // read/write access
                            FALSE,                 // do not inherit the name
                            MAP_FILE_ADD_NEW_GROUP);               // name of mapping object
    if (hMapFile == NULL)
    {
        QMessageBox::information( NULL, "L?i ph?n m?m","L?i OpenFileMapping, B?n hÃ£y kh?i d?ng l?i ph?n m?m" );
        return 1;
    }
    pBuf = (char*) MapViewOfFile(hMapFile,   // handle to map object
                                            FILE_MAP_ALL_ACCESS,             // read/write permission
                                            0,
                                            0,
                                            BUF_SIZE);
            if (pBuf == NULL)
            {
                    QMessageBox::information( NULL, "loi","khong the map view file" );
                    return 2;
            }
            CopyMemory((PVOID) pBuf, qstrDataSend.toStdString().data(), qstrDataSend.length());
            HANDLE hEvent = OpenEventA(EVENT_ALL_ACCESS, FALSE, EVENT_ADD_NEW_GROUP);
                SetEvent(hEvent);
    return a.exec();
}

#include <QtCore/QCoreApplication>
#include <QtGui/QMessageBox>
#include <QString>
#include <windows.h>

#define BUF_SIZE  1024
#define MAP_FILE_ADD_NEW_GROUP  "Local\\MyFileMappingAddNewGroup"
#define EVENT_ADD_NEW_GROUP     "Local\\eventaddnewgroup"


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    HANDLE hMapFile;
    char* pBuf;

    QString qstrDataSend = "ADDKJHGFDSDFGHJ";
    hMapFile = OpenFileMappingA(
                            FILE_MAP_ALL_ACCESS,   // read/write access
                            FALSE,                 // do not inherit the name
                            MAP_FILE_ADD_NEW_GROUP);               // name of mapping object
    if (hMapFile == NULL)
    {
        QMessageBox::information( NULL, "L?i ph?n m?m","L?i OpenFileMapping, B?n hÃ£y kh?i d?ng l?i ph?n m?m" );
        return 1;
    }
    pBuf = (char*) MapViewOfFile(hMapFile,   // handle to map object
                                            FILE_MAP_ALL_ACCESS,             // read/write permission
                                            0,
                                            0,
                                            BUF_SIZE);
            if (pBuf == NULL)
            {
                    QMessageBox::information( NULL, "loi","khong the map view file" );
                    return 2;
            }
            CopyMemory((PVOID) pBuf, qstrDataSend.toStdString().data(), qstrDataSend.length());
            HANDLE hEvent = OpenEventA(EVENT_ALL_ACCESS, FALSE, EVENT_ADD_NEW_GROUP);
                SetEvent(hEvent);
    return a.exec();
}

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**stampede** · 4th July 2011, 15:42

If you want to use QtGui, then you have to instantiate QApplication object, QCoreApplication is not enough to use message windows, change this

Qt Code:

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#include <QtCore/QCoreApplication>
...
QCoreApplication a(argc, argv);

#include <QtCore/QCoreApplication>
...
QCoreApplication a(argc, argv);

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to

Qt Code:

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#include <QApplication>
...
QApplication a(argc, argv);

#include <QApplication>
...
QApplication a(argc, argv);

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**ThÃ nh ViÃªn Má»›i** · 8th July 2011, 17:42

thanks you, i was fix Widgets must be created in the GUI thread on SendEvent, but when i run test-gui-event-error project and after run sendevent project then it still error on test-gui-event-error

this is error debug on QtCreator

in c:\ndk_buildrepos\qt-desktop\src\corelib\global\qglobal.cpp
0x6a10e211 <+000>: push %ebp
0x6a10e212 <+001>: mov %esp,%ebp
0x6a10e214 <+003>: sub $0x18,%esp
2027 in c:\ndk_buildrepos\qt-desktop\src\corelib\global\qglobal.cpp
0x6a10e217 <+006>: mov 0x10(%ebp),%eax
0x6a10e21a <+009>: mov %eax,0xc(%esp)
0x6a10e21e <+013>: mov 0xc(%ebp),%eax
0x6a10e221 <+016>: mov %eax,0x8(%esp)
0x6a10e225 <+020>: mov 0x8(%ebp),%eax
0x6a10e228 <+023>: mov %eax,0x4(%esp)
0x6a10e22c <+027>: movl $0x6a2e3e50,(%esp)
0x6a10e233 <+034>: call 0x6a10ebf0 <qFatal(const char *, ...)>
2028 in c:\ndk_buildrepos\qt-desktop\src\corelib\global\qglobal.cpp
0x6a10e238 <+039>: leave
0x6a10e239 <+040>: ret

QtCenter-VietNam.zip

**ThÃ nh ViÃªn Má»›i** · 10th July 2011, 15:54

can you help me ?

**ThÃ nh ViÃªn Má»›i** · 8th November 2011, 10:13

can you help me ???

(

**nightghost** · 8th November 2011, 12:03

try to change

Qt Code:

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connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)),Qt::DirectConnection );

connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)),Qt::DirectConnection );

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to

Qt Code:

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connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)));

connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)));

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or

Qt Code:

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connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)), Qt::QueuedConnection);

connect(tWAGE,SIGNAL(AddNewGroup(QList<QString>)),this,SLOT(prepareAddGroup(QList<QString>)), Qt::QueuedConnection);

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see http://doc.trolltech.com/4.5/threads...across-threads

**ThÃ nh ViÃªn Má»›i** · 8th November 2011, 16:48

it still error

when i play QmessageBOx in Qthread then it still also error

help me resolve

**nightghost** · 8th November 2011, 16:53

Yes of course. Please read http://doc.qt.nokia.com/4.7-snapshot/thread-basics.html

As mentioned, each program has one thread when it is started. This thread is called the "main thread" (also known as the "GUI thread" in Qt applications). The Qt GUI must run in this thread. All widgets and several related classes, for example QPixmap, work in secondary threads.

To be clear: Its (by the design of Qt) not possible to work with widgets in threads. The work only in the main thread! Inform the main thread from your worker thread to show the message box.

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