Check has created with new

[wirasto]

How to check object has created with new ? I tried like this, but not work

Tahede *_tahede;
//_tahede=new Tahede(this);
if (_tahede)
{
	qDebug() << "Created before";
 
	_tahede->exec();
}
else
{
	qDebug() << "Create now";
 
	_tahede=new Tahede(this);
	_tahede->exec();
}

Tahede *_tahede;
//_tahede=new Tahede(this);
if (_tahede)
{
	qDebug() << "Created before";

	_tahede->exec();
}
else
{
	qDebug() << "Create now";

	_tahede=new Tahede(this);
	_tahede->exec();
}

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Application output window only give me message...

Created before
QDialog::exec: Recursive call detected

[toreo]

If you intend there to be only one Tahede instance in your program, please look at the singleton pattern. If you want to have a delayed construction of a member variable, you need to initialize it to 0 first. Perhaps the following would work (might not compile verbatim, inline code for a brief example):

class MyObject : public QObject
{
public:
    MyObject() : _tahede(0) {}
 
    void doExec() {
        tahede()->exec();
    }
 
protected:
    Tahede* tahede() {
        if(!_tahede)
            _tahede = new Tahede(this);
        return _tahede;
    }
 
private:
    Tadede* _tahede;
};

class MyObject : public QObject
{
public:
    MyObject() : _tahede(0) {}

    void doExec() {
        tahede()->exec();
    }

protected:
    Tahede* tahede() {
        if(!_tahede)
            _tahede = new Tahede(this);
        return _tahede;
    }

private:
    Tadede* _tahede;
};

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[wirasto]

Thanks for your replay. But, how delete that object. I modified your code sample...

void doExec() {
        tahede()->exec();
    }
 
    void doDelete() {
        delete _tahede;
    }
 
protected:
    void changeEvent(QEvent *e);
 
    Tahede* tahede() {
        if(!_tahede)
        {
            _tahede = new Tahede(this);
 
            qDebug() << "Create now";
        }
        else
        {
            qDebug() << "Created before";
        }
        return _tahede;
    }
 
private:
    Tahede* _tahede;

void doExec() {
        tahede()->exec();
    }

    void doDelete() {
        delete _tahede;
    }

protected:
    void changeEvent(QEvent *e);

    Tahede* tahede() {
        if(!_tahede)
        {
            _tahede = new Tahede(this);

            qDebug() << "Create now";
        }
        else
        {
            qDebug() << "Created before";
        }
        return _tahede;
    }

private:
    Tahede* _tahede;

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void Dialog::on_pushButton_clicked()
{
    doExec();
}
 
void Dialog::on_pushButton_2_clicked()
{
    doDelete();
}

void Dialog::on_pushButton_clicked()
{
    doExec();
}

void Dialog::on_pushButton_2_clicked()
{
    doDelete();
}

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After I deleted with doDelete() function, and doExec() again, Application output still give me message "Created before" and my application crash What's wrong ?

[dbzhang800]

when you delete your object, your had better:

delete _tahede;
_tahede = 0;

[faldzip]

or use a QPointer whis sets automagicaly itself to 0 when the object is deleted:

private:
    QPointer<Tadede> _tahede;
};

private:
    QPointer<Tadede> _tahede;
};

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[cafu]

Hi There,

i have a small problem while casting from QPointer<T> to QPointer<ChildT>

I tried this.

QPointer<T> tObject=new T();
//QPointer<ChildT> childtObject=(QPointer<T>)tObjec;// this does not work;
QPointer<ChildT> childtObject=(ChildT*)(T*)tObjec;// this work;