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V1110. Constructor of a class inherited from 'QObject' does not use a pointer to a parent object.
The analyzer has detected a class inherited from the 'QObject' type. It has a constructor that accepts a pointer to 'QObject' as a parameter, but it does not use it to organize a parent-child relationship.
The 'QObject'-derived objects are organized into trees with the parent-child relationships. When another object is created, the pointer to the parent object is passed. In the parent object, the created object is added to the children list. This guarantees that when the parent object is deleted, all of its child objects will also be deleted.
Consider the example:
class BadExample : public QObject
{
public:
BadExample(QObject *parent) : ui(new UI::BadExample)
{
ui->setupUi(this);
};
};The pointer to the parent object is passed to the constructor of the 'BadExample' class. However, the pointer is not passed to the base class constructor and is not used in the constructor body.
Here's the fixed example:
class GoodExample1 : public QObject
{
public:
GoodExample1(QObject *parent)
: QObject (parent), ui(new UI::GoodExample)
{
/*....*/
};
};The analyzer does not issue the warning in the following cases.
Case N1. The parameter is unnamed. This indicates that the programmer has chosen not to pass control of the object to the Qt:
class GoodExample2 : public QObject
{
public:
GoodExample2(QObject *) { /* .... */ };
};Case N2. The parameter is deliberately not used to organize the parent-child relationship. The null pointer is explicitly passed to the constructor of the parent class:
class GoodExample3 : public QObject
{
public:
GoodExample3(QObject *parent) : QObject { nullptr } { /* .... */ };
};Case N3. The parameter is passed to the QObject::setParent function:
class GoodExample4 : public QObject
{
public:
GoodExample4(QObject *parent)
{
setParent(parent);
};
};This diagnostic is classified as:
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