Error on build..QThread class

[freekill]

I'm working on my multi-threaded project and got this error on build. I did not require any initialization with my threads and I just made an instance of the thread in the private section of my QMainWindow.
error: field 'capturingThread' has incomplete type
error: field 'computingThread' has incomplete type
The following code is my main window and the error points to the private section here.

#ifndef GENIUS_H
#define GENIUS_H
 
#include <QMainWindow>
#include "ui_genius.h"
 
class CapturingThread;
class ComputingThread;
 
class GeniusMain : public QMainWindow, private Ui::genius
{
    Q_OBJECT
 
    public:
       GeniusMain(QMainWindow *parent);
 
    protected:
       void closeEvent (QCloseEvent *event);
 
    private slots:
       void standbyThreads();
       void startTransmission();
       void haltThreads();
       void printFPS();
       void printDistance();
       void printTeam();
       void printOpp();
 
    private:
       CapturingThread capturingThread;
       ComputingThread computingThread;
};
 
#endif

#ifndef GENIUS_H
#define GENIUS_H

#include <QMainWindow>
#include "ui_genius.h"

class CapturingThread;
class ComputingThread;

class GeniusMain : public QMainWindow, private Ui::genius
{
    Q_OBJECT

    public:
       GeniusMain(QMainWindow *parent);

    protected:
       void closeEvent (QCloseEvent *event);

    private slots:
       void standbyThreads();
       void startTransmission();
       void haltThreads();
       void printFPS();
       void printDistance();
       void printTeam();
       void printOpp();

    private:
       CapturingThread capturingThread;
       ComputingThread computingThread;
};

#endif

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Here are the header files for my threads capturingThread and computingThread.

#ifndef CAPTURINGTHREAD_H
#define CAPTURINGTHREAD_H
 
#include <QThread>
 
class ImageBuffer;
 
class CapturingThread : public QThread 
{
    public:
       CapturingThread();
       ~CapturingThread();
 
       void haltCapture();
 
    protected:
       void run();
 
    private:
       volatile bool halt;
       ImageBuffer* imageBuffer;
};
 
#endif

#ifndef CAPTURINGTHREAD_H
#define CAPTURINGTHREAD_H

#include <QThread>

class ImageBuffer;

class CapturingThread : public QThread 
{
    public:
       CapturingThread();
       ~CapturingThread();

       void haltCapture();

    protected:
       void run();

    private:
       volatile bool halt;
       ImageBuffer* imageBuffer;
};

#endif

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#ifndef COMPUTINGTHREAD_H
#define COMPUTINGTHREAD_H
 
#include <QThread>
 
class ImageBuffer;
 
class ComputingThread : public QThread
{
    public:
       ComputingThread();
       ~ComputingThread();
 
       void haltComputing();
       void startTransmitting();
       void stopTransmitting();
 
    protected:
       void run();
 
    private:
       volatile bool halt;
       volatile bool transmit;
       ImageBuffer* imageBuffer;
};
 
#endif

#ifndef COMPUTINGTHREAD_H
#define COMPUTINGTHREAD_H

#include <QThread>

class ImageBuffer;

class ComputingThread : public QThread
{
    public:
       ComputingThread();
       ~ComputingThread();

       void haltComputing();
       void startTransmitting();
       void stopTransmitting();

    protected:
       void run();

    private:
       volatile bool halt;
       volatile bool transmit;
       ImageBuffer* imageBuffer;
};

#endif

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What could be the source of the build error?

[tsp]

My guess would be that forward declaration i.e. code below:

class CapturingThread;
class ComputingThread;

class CapturingThread;
class ComputingThread;

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Works for pointers but not for objects (see code below).

private:
       CapturingThread capturingThread;
       ComputingThread computingThread;

private:
       CapturingThread capturingThread;
       ComputingThread computingThread;

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So either include both header files (computingthread.h / capturingthread.h) in genius.h file or use next piece of code:

private:
       CapturingThread *capturingThread;
       ComputingThread *computingThread;

private:
       CapturingThread *capturingThread;
       ComputingThread *computingThread;

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And then allocate the memory for those objects when you need them.