Communication between QThread and Yes/No QMessageBox?

[pmaktieh.sirhc]

Nothing, it's not implemented yet! It's a consideration so far!

[spurious_interrupt]

I have an application that uses tape drives. The thread needs to ask if there are any more tapes for the job, SCSI errors, file dialogs...

This method uses QT3, I have not ported this application to QT4 yet.

in your application
 
void  TapeMan::customEvent( QCustomEvent *event )
{
 if( event->type() == QEvent::User + 3 ) // display message box
    {
    MessageBoxEvent  *me = ( MessageBoxEvent* )event;
    ThreadMessageBox  *tm = me->tm;
 
    if( me->kind == TMSG_WARN )
        tm->messageResult = QMessageBox::warning( this, me->caption, me->message, 
                me->button0, me->button1, me->button2 );
    if( me->kind == TMSG_INFO )
        tm->messageResult = QMessageBox::information( this, me->caption, 
                me->message, me->button0, me->button1, me->button2 );
    if( me->kind == TMSG_STOP )
        tm->messageResult = QMessageBox::critical( this, me->caption, me->message, 
                me->button0, me->button1, me->button2 );
    }
}
 
and then 2 classes
 
#ifndef THREADMESSAGEBOX_H
#define THREADMESSAGEBOX_H
 
#include  <qstring.h>
#include  <qmessagebox.h>
 
class ThreadMessageBox
{
public: 
	ThreadMessageBox( THREAD_MESSAGE kind, const QString &caption, const 
                QString& message, int button0, int button1=QMessageBox::NoButton, 
                int button2=QMessageBox::NoButton );
 
	~ThreadMessageBox();
 
	int  messageResult;
};
 
#endif
 
#include  "threadmessagebox.h"
#include  "messageboxevent.h"
 
#include  <qapplication.h>
 
extern TapeMan  *gApp;
 
ThreadMessageBox::ThreadMessageBox( THREAD_MESSAGE kind, const QString &caption,
                const QString& message, int button0, int button1, int button2 )
{
    MessageBoxEvent  *mess = new  MessageBoxEvent( this, kind, caption, message, 
                button0, button1, button2 );
 
    messageResult = -99999;
 
    QApplication::postEvent( gApp, mess );	// post event
 
    while( messageResult == -99999 )         // wait
        {
        sleep( 1 );
        }
}
 
ThreadMessageBox::~ThreadMessageBox()
{
}
 
#ifndef MESSAGE_BOX_EVENT_H
#define MESSAGE_BOX_EVENT_H
 
#include  <qevent.h>
#include  <qmessagebox.h>
#include  <qdeepcopy.h>
 
class  ThreadMessageBox;
 
class MessageBoxEvent : public QCustomEvent
{
public: 
    MessageBoxEvent( ThreadMessageBox *tm, THREAD_MESSAGE kind, const QString &caption,
                const QString& message, int button0, int button1=QMessageBox::NoButton, 
                int button2=QMessageBox::NoButton );
    ~MessageBoxEvent();
 
   THREAD_MESSAGE  kind;	// kind of message box
 
    QDeepCopy<QString>  caption;	// caption for message box
    QDeepCopy<QString>  message;	// text for message
 
    int  button0;			// buttons to display
    int  button1;
    int  button2;
 
    ThreadMessageBox  *tm;		// pointer to thread message box
};
#endif
 
#include "messageboxevent.h"
 
MessageBoxEvent::MessageBoxEvent( ThreadMessageBox *tm, THREAD_MESSAGE kind, 
                const QString &caption, const QString& message,
                int button0, int button1, int button2 ) : QCustomEvent( QEvent::User+3 )
{
    this->kind    = kind;
    this->caption = caption;
    this->message = message;
    this->button0 = button0;
    this->button1 = button1;
    this->button2 = button2;
    this->tm = tm;
}
 
MessageBoxEvent::~MessageBoxEvent()
{
}
 
to get a message box from your thread
 
    ThreadMessageBox  mess = ThreadMessageBox( TMSG_INFO, "Tape Done", "Are there any more tapes",
                QMessageBox::Yes, QMessageBox::No );  // will block until message box is closed
 
    if( mess.messageResult == QMessageBox::Yes )
        // do action here!

in your application

void  TapeMan::customEvent( QCustomEvent *event )
{
 if( event->type() == QEvent::User + 3 ) // display message box
    {
    MessageBoxEvent  *me = ( MessageBoxEvent* )event;
    ThreadMessageBox  *tm = me->tm;

    if( me->kind == TMSG_WARN )
        tm->messageResult = QMessageBox::warning( this, me->caption, me->message, 
                me->button0, me->button1, me->button2 );
    if( me->kind == TMSG_INFO )
        tm->messageResult = QMessageBox::information( this, me->caption, 
                me->message, me->button0, me->button1, me->button2 );
    if( me->kind == TMSG_STOP )
        tm->messageResult = QMessageBox::critical( this, me->caption, me->message, 
                me->button0, me->button1, me->button2 );
    }
}

and then 2 classes

#ifndef THREADMESSAGEBOX_H
#define THREADMESSAGEBOX_H

#include  <qstring.h>
#include  <qmessagebox.h>

class ThreadMessageBox
{
public: 
	ThreadMessageBox( THREAD_MESSAGE kind, const QString &caption, const 
                QString& message, int button0, int button1=QMessageBox::NoButton, 
                int button2=QMessageBox::NoButton );

	~ThreadMessageBox();

	int  messageResult;
};

#endif

#include  "threadmessagebox.h"
#include  "messageboxevent.h"

#include  <qapplication.h>

extern TapeMan  *gApp;

ThreadMessageBox::ThreadMessageBox( THREAD_MESSAGE kind, const QString &caption,
                const QString& message, int button0, int button1, int button2 )
{
    MessageBoxEvent  *mess = new  MessageBoxEvent( this, kind, caption, message, 
                button0, button1, button2 );

    messageResult = -99999;

    QApplication::postEvent( gApp, mess );	// post event

    while( messageResult == -99999 )         // wait
        {
        sleep( 1 );
        }
}

ThreadMessageBox::~ThreadMessageBox()
{
}

#ifndef MESSAGE_BOX_EVENT_H
#define MESSAGE_BOX_EVENT_H

#include  <qevent.h>
#include  <qmessagebox.h>
#include  <qdeepcopy.h>

class  ThreadMessageBox;

class MessageBoxEvent : public QCustomEvent
{
public: 
    MessageBoxEvent( ThreadMessageBox *tm, THREAD_MESSAGE kind, const QString &caption,
                const QString& message, int button0, int button1=QMessageBox::NoButton, 
                int button2=QMessageBox::NoButton );
    ~MessageBoxEvent();

   THREAD_MESSAGE  kind;	// kind of message box

    QDeepCopy<QString>  caption;	// caption for message box
    QDeepCopy<QString>  message;	// text for message

    int  button0;			// buttons to display
    int  button1;
    int  button2;

    ThreadMessageBox  *tm;		// pointer to thread message box
};
#endif

#include "messageboxevent.h"

MessageBoxEvent::MessageBoxEvent( ThreadMessageBox *tm, THREAD_MESSAGE kind, 
                const QString &caption, const QString& message,
                int button0, int button1, int button2 ) : QCustomEvent( QEvent::User+3 )
{
    this->kind    = kind;
    this->caption = caption;
    this->message = message;
    this->button0 = button0;
    this->button1 = button1;
    this->button2 = button2;
    this->tm = tm;
}

MessageBoxEvent::~MessageBoxEvent()
{
}

to get a message box from your thread

    ThreadMessageBox  mess = ThreadMessageBox( TMSG_INFO, "Tape Done", "Are there any more tapes",
                QMessageBox::Yes, QMessageBox::No );  // will block until message box is closed

    if( mess.messageResult == QMessageBox::Yes )
        // do action here!

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You need to use QDeepCopy's to insure each thread has a unique copy of the strings. This is not needed in QT4. The wait loop is a simple sleep. That is all that was needed for this application.

[spud]

As long as the tQThread object was created in the Gui thread, you can set up a connection between a private signal and a private slot. For the synchronization you need a QWaitCondition and a QMutex.
e.g.:

class WorkingThread : public QThread
{
	Q_OBJECT
public:
	WorkingThread(QObject*parent=0);
protected:
	virtual void run();
signals:
	void askAQuestion( const QString& question, QMessageBox::StandardButton* answer);
private slots:
	void questionAsked(const QString& question, QMessageBox::StandardButton* answer);
private:
	QWaitCondition waitCondition;
	QMutex mutex;
};
 
WorkingThread::WorkingThread(QObject*parent) 
	: QThread(parent=0)
{
	connect(this, SIGNAL(askAQuestion( const QString&, QMessageBox::StandardButton*)), 
		this, SLOT(questionAsked( const QString&, QMessageBox::StandardButton*)));
}
 
void WorkingThread::run()
{
	QMessageBox::StandardButton answer = QMessageBox::Yes;
	do
	{
		QMutexLocker locker(&mutex);
		emit askAQuestion( "do you want to continue?", &answer);
		waitCondition.wait(&mutex);
	}
	while(answer == QMessageBox::Yes);
}
 
void WorkingThread::questionAsked(const QString& question, QMessageBox::StandardButton* answer)
{
	QMutexLocker locker(&mutex);
	*answer = QMessageBox::question(0, "Question:", question, QMessageBox::Yes|QMessageBox::No);
	waitCondition.wakeOne();
}

class WorkingThread : public QThread
{
	Q_OBJECT
public:
	WorkingThread(QObject*parent=0);
protected:
	virtual void run();
signals:
	void askAQuestion( const QString& question, QMessageBox::StandardButton* answer);
private slots:
	void questionAsked(const QString& question, QMessageBox::StandardButton* answer);
private:
	QWaitCondition waitCondition;
	QMutex mutex;
};

WorkingThread::WorkingThread(QObject*parent) 
	: QThread(parent=0)
{
	connect(this, SIGNAL(askAQuestion( const QString&, QMessageBox::StandardButton*)), 
		this, SLOT(questionAsked( const QString&, QMessageBox::StandardButton*)));
}

void WorkingThread::run()
{
	QMessageBox::StandardButton answer = QMessageBox::Yes;
	do
	{
		QMutexLocker locker(&mutex);
		emit askAQuestion( "do you want to continue?", &answer);
		waitCondition.wait(&mutex);
	}
	while(answer == QMessageBox::Yes);
}

void WorkingThread::questionAsked(const QString& question, QMessageBox::StandardButton* answer)
{
	QMutexLocker locker(&mutex);
	*answer = QMessageBox::question(0, "Question:", question, QMessageBox::Yes|QMessageBox::No);
	waitCondition.wakeOne();
}

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The connection will automatically be queued since the run() function doesn't reside in the same thread as the QThread object, thus it's safe to use a messagebox.

Good luck!