create a Class inherits from two QObject subclasses

[sabeesh]

Hi,

How can I create a Class inherits from two QObject subclasses in Qt 4.3 ?

Eg:

class MyClass:: public Class1 , protected QThread 
{
   .......
}

class MyClass:: public Class1 , protected QThread 
{
   .......
}

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Please help me.

[marcel]

It is not possible to inherit from 2 QObject classes. Instead inherit only the first one and make your class to be a wrapper around QThread - it doesn't have that many methods anyway. Create a QThread member and expose its API through your class.

EDIT: look at this... eclipse even tells you you can't inherit from two QObject's:

[sabeesh]

Hi,
I am not very clear with your answer. Can you please give an sample code for it ?

[sabeesh]

Hi,
How can I solve this problem?
Please help me

[marcel]

class MyClass : public Class1
{
Q_OBJECT
 
protected:
 MyThread *mThread;
 
public:
 MyClass(QObject* = NULL);
 ~MyClass();
 
  //expose QThread API
  void start() {
   mThread->start();
  } 
  .. you can add other QThread methods and slots here
}

class MyClass : public Class1
{
Q_OBJECT

protected:
 MyThread *mThread;

public:
 MyClass(QObject* = NULL);
 ~MyClass();

  //expose QThread API
  void start() {
   mThread->start();
  } 
  .. you can add other QThread methods and slots here
}

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Here MyThread is a QThread subclass.

[sabeesh]

Hi,
When I try this, at the time of running the program, Qt display an error like this

First-chance exception at 0x67015e8a (QtCored4.dll) in Test.exe: 0xC0000005: Access violation reading location 0xcdcdcdd1.
Unhandled exception at 0x67015e8a (QtCored4.dll) in Test.exe: 0xC0000005: Access violation reading location 0xcdcdcdd1.

Please help me to solve this problem.

[jpn]

You're dereferencing an uninitialized pointer. Do you have something like

mThread = new MyThread(this);

mThread = new MyThread(this);

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anywhere in your code?

[sabeesh]

Hi
My code is like this

{
protected:
	QThread *mThread;
       ........
 
public:
    void start() {
		mThread->start();
	} 
	virtual void run();
 
}

{
protected:
	QThread *mThread;
       ........

public:
    void start() {
		mThread->start();
	} 
	virtual void run();

}

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and in my .cpp file the code is like this

void CTest::StartCapture (int DeviceNum ){
 
	capture = cvCaptureFromCAM( DeviceNum );
 
	if( !capture ) {
		 fprintf( stderr, "ERROR: capture is NULL \n" );
		 getchar();
	}
	mThread->start();
 
}
 
 
void CWebCamViewer::run() {
 
	while( true ) {
		// Get one frame
		qApp->processEvents();
				ImgFrame = cvQueryFrame( capture );
				if( !ImgFrame ) {
					fprintf( stderr, "ERROR: frame is null...\n" );
					getchar();
					break;
				}
				ReturnImg = IplImageToQImage(ImgFrame);
				hflip =  ReturnImg->transformed(QMatrix().scale(1,-1));
				hflip = hflip.scaled(320,240, Qt::IgnoreAspectRatio, Qt::FastTransformation);
				Picture->setPixmap(QPixmap::fromImage(hflip));
		}
}

void CTest::StartCapture (int DeviceNum ){

	capture = cvCaptureFromCAM( DeviceNum );

	if( !capture ) {
		 fprintf( stderr, "ERROR: capture is NULL \n" );
		 getchar();
	}
	mThread->start();

}


void CWebCamViewer::run() {

	while( true ) {
		// Get one frame
		qApp->processEvents();
				ImgFrame = cvQueryFrame( capture );
				if( !ImgFrame ) {
					fprintf( stderr, "ERROR: frame is null...\n" );
					getchar();
					break;
				}
				ReturnImg = IplImageToQImage(ImgFrame);
				hflip =  ReturnImg->transformed(QMatrix().scale(1,-1));
				hflip = hflip.scaled(320,240, Qt::IgnoreAspectRatio, Qt::FastTransformation);
				Picture->setPixmap(QPixmap::fromImage(hflip));
		}
}

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Please help me to solve that problum.

[jpn]

Could you answer my question?

[sabeesh]

Hi,
No, I didn't give a line like this

mThread = new MyThread(this);

mThread = new MyThread(this);

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in my program

[jpn]

So most likely mThread is an uninitialized pointer which points to 0xcdcdcdd1. Don't you think you should have

mThread = new QThread(this);

mThread = new QThread(this);

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somewhere?

[sabeesh]

Hi
When I give the command in my constructor

mThread = new QThread(this);

mThread = new QThread(this);

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then Qt return an error like this

.\Test.cpp(70) : error C2259: 'QThread' : cannot instantiate abstract class
due to following members:
'void QThread::run(void)' : is abstract
c:\qt\4.3.0\include\qtcore\qthread.h(87) : see declaration of 'QThread::run'

[jpn]

Ahh, indeed. QThread will be non-abstract in Qt 4.4 but until that you will have to implement QThread::run().

[sabeesh]

Hi,
In my code I had implement the run(). Please see the code , which one i previous declare.

in .h file

virtual void run();

virtual void run();

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and in .cpp file

void CTest::run() {
  .....
  .....
 }

void CTest::run() {
  .....
  .....
 }

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is it correct?

[jpn]

A friendly advise would be to learn C++ before trying to use a comprehensive toolkit written in C++. Using Qt sure requires some knowledge of C++.

What you have shown above declares a method "virtual void run()" in a class which has QThread pointer as a member. That's not at all same than implementing QThread::run().

Notice the difference between:

class Foo : public QObject
{
protected:
  virtual void run() { ... }
 
  QThread* mThread;
};

class Foo : public QObject
{
protected:
  virtual void run() { ... }
  
  QThread* mThread;
};

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and

class MyThread : public QThread
{
protected:
  virtual void run() { ... }
};
 
class Bar : public QObject
{
protected:
  MyThread* mThread;
};

class MyThread : public QThread
{
protected:
  virtual void run() { ... }
};

class Bar : public QObject
{
protected:
  MyThread* mThread;
};

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[sabeesh]

Hi,
Its my mistake. Sorry.

I create a class like this

class MyThread : public QThread
{
 
  protected:
	  virtual void run(){
		  while(true){
		  qDebug()<<"Run";
                   } 
	  }
 
};

class MyThread : public QThread
{

  protected:
	  virtual void run(){
		  while(true){
		  qDebug()<<"Run";
                   } 
	  }

};

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and in .h file

QThread *mThread;

QThread *mThread;

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and give the command in my constructor like this

mThread = new QThread(this);

mThread = new QThread(this);

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but the error is like this

.\Test.cpp(70) : error C2259: 'QThread' : cannot instantiate abstract class
        due to following members:
        'void QThread::run(void)' : is abstract
        c:\qt\4.3.0\include\qtcore\qthread.h(87) : see declaration of 'QThread::run'

.\Test.cpp(70) : error C2259: 'QThread' : cannot instantiate abstract class
        due to following members:
        'void QThread::run(void)' : is abstract
        c:\qt\4.3.0\include\qtcore\qthread.h(87) : see declaration of 'QThread::run'

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Please help me

[marcel]

QThread is abstract. You must instantiate your QThread subclass:

mThread = new MyThread(this);

mThread = new MyThread(this);

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[sabeesh]

Hi,
Ohhhh, It's my mistake. Sorry.
Thankyou for your help