How to create a "node" using QObject

[d_stranz]

Could you explain what you meant by the "Add connection child" comment?

It means "write the code here that you need to insert the child node into whatever data structure you are using to hold the information in the tree you are building".

If your CFCAbstract hierarchy is all QObject-based (i.e. CFCAbstract inherits from QObject) then this could be as simple as:

bool CFCInterface::addChild( CFCAbstract * pChild )
{
    CFCConnection * pConn = qobject_cast< CFCConnection * >( pChild );
    if ( pConn != nullptr )
    {
        pConn->setParent( this );
        return true;
    }
    return false;
}

bool CFCInterface::addChild( CFCAbstract * pChild )
{
    CFCConnection * pConn = qobject_cast< CFCConnection * >( pChild );
    if ( pConn != nullptr )
    {
        pConn->setParent( this );
        return true;
    }
    return false;
}

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But if I were doing this, I would implement a customized tree model that stored this structure independently of the view, then wrap it into a QAbstractItemModel for display in a QTreeView. See the Qt Simple Tree Model example.

To translate that example to yours, "TreeItem" is replaced everywhere by "CFCAbstract", and all of the specific types derive from the CFCAbstract base class (which itself no longer derives from QObject; it's just an ordinary C++ class). The appendChild() method is what I called "addChild()" above, and would have to be made a virtual method and reimplemented in each class derived from CFCAbstract in order to implement your rules for what can be added where.

[cryomicl]

@d_stranz
Thank you so very much!! As you can see, my knowledge in Qt is fairly limited. But with the help of supportive experts like you, people like me will surely learn!

[cryomicl]

@d_stranz
I tried implementing the code, but there was no change in the GUI. By using breakpoints I found that the qobjectcast was returning a null pointer (pConn ==nullptr). Could you take a stab at why this could possibly be happening?

[d_stranz]

Is the CFCConnection class derived from QObject somewhere in its inheritance hierarchy? Is the Q_OBJECT macro present in the class definition in the header file? Is MOC being run on the header file?

[cryomicl]

Is the CFCConnection class derived from QObject somewhere in its inheritance hierarchy? Is the Q_OBJECT macro present in the class definition in the header file? Is MOC being run on the header file?

Yes, yes and yes.

The code to demonstrate the first two points:

#include <QObject>  //Included QObject
#include "ResourceItem.h"
#include "MonWindow.h"
#include "FCTab.h"
#include "ResourceItem.h"
#include "FCAbstract.h"
#include "FCInterface.h"
 
class CFCConnections: public CResourceItem
{
 
    Q_OBJECT  //QObject MACRO
 
public:
	CFCConnections(QObject*);
	~CFCConnections();
 
private:
	CFCInterface*					pParent;
 
 
};
 
 
#endif

#include <QObject>  //Included QObject
#include "ResourceItem.h"
#include "MonWindow.h"
#include "FCTab.h"
#include "ResourceItem.h"
#include "FCAbstract.h"
#include "FCInterface.h"

class CFCConnections: public CResourceItem
{

    Q_OBJECT  //QObject MACRO
    
public:
	CFCConnections(QObject*);
	~CFCConnections();

private:
	CFCInterface*					pParent;

	
};


#endif

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That was the FCConnections.h code. And I know that MOC has run on the header file because I had to manually change its build step to include MOC. This image below shows the inheritance hierarchy. CFCConnections is derived from CResourceItem which has QObject as its base class.
1.jpg

POSSIBLE SOLUTION

I just had to change the line

CFCConnections* f_pConn=0;

CFCConnections* f_pConn=0;

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to

CFCConnections* f_pConn;
f_pConn = new CFCConnections(this);

CFCConnections* f_pConn;
f_pConn = new CFCConnections(this);

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[d_stranz]

I just had to change the line

So you mean to say you were trying to add a NULL pointer to an instance of CFCConnection to your hierarchy? Of course that won't work. qobject_cast<> won't magically turn a NULL or uninitialized pointer into a real one, it turns a real pointer to some QObject-based class into a pointer to another QObject-based class if the conversion is valid (that is, the type you are trying to cast to inherits from the type that is passed in).

[cryomicl]

Of course that won't work. qobject_cast<> won't magically turn a NULL or uninitialized pointer into a real one.

Now I know this from experience, the best way to never forget a lesson.
Thank you for all your help