Class definition issue

gabor53

Hi,
I have the following class in mydelegate.h:

#ifndef MYDELEGATE_H
#define MYDELEGATE_H

#include <QObject>
#include <QWidget>
#include <QStyledItemDelegate>
#include <QStyleOptionViewItem>
#include <QLineEdit>
#include <QDebug>

namespace Ui
{
class myDelegate;
}

class myDelegate : public QStyledItemDelegate
{
    Q_OBJECT

public:
    explicit myDelegate(QWidget *parent = nullptr);

The mydelegate.cpp:

#include "mydelegate.h"


myDelegate::myDelegate(QWidget *parent)
{
}

Whenever I run it I get the following warning:
C:\Programming\Projects\Folkfriends_1_0\mydelegate.cpp:4: warning: unused parameter 'parent' [-Wunused-parameter]
myDelegate::myDelegate(QWidget *parent)
^
Everything works.Do I need to worry about this (and other unused parameter) warning?
Thank you.

Chris Kawa

@gabor53 said:

Do I need to worry about this (and other unused parameter) warning?

Yes, because it uncovered a serious bug in your code. In your constructor definition you're not passing the parameter to the base class constructor, so it calls a default base constructor, making your instance not having a parent (and thus creating a memory leak).

When creating QObject derived classes always pass the parent parameter to the base class constructor:

myDelegate::myDelegate(QWidget* parent) : QStyledItemDelegate(parent)
{
}

Btw. It's unusual that an item delegate would need a parent QWidget. QObject should be enough:

//.h
explicit myDelegate(QObject* parent = nullptr);

//.cpp
myDelegate::myDelegate(QObject* parent) : QStyledItemDelegate(parent)

gabor53

@Chris-Kawa
Thank you. It worked.