How to use qobject_cast with inherited class

[HenkCoder]

Hello everyone, I have created a class called TextEdit, which inherits from QTextEdit.
On my mainwindow I have a tabWidget and everytime I create a new tab a TextEdit should appear.
But that's not the problem.
How can I use qobject_cast to access the widget inside of the tab?
Cause now whenever I try it says:

C:\Qt\6.1.2\mingw81_64\include\QtCore\qobject.h:449: error: static assertion failed: qobject_cast requires the type to have a Q_OBJECT macro

The code to get the textedit is this:

TextEdit* MainWindow::getTabTextEdit()
{
    return qobject_cast<TextEdit*>(ui->tabWidget->widget(ui->tabWidget->currentIndex()));
}

Can you help me please?

[J.Hilk]

@HenkCoder said in How to use qobject_cast with inherited class:

How do I make the thing with Q_OBJECT macro then?

class TextEdit : public QTextEdit
{
    Q_OBJECT
public:

and since we're at it, lets do a proper constructor for a Qt class as well:

public:
   explicit TextEdit(QWidget *parent = nullptr) : QTextEdit(parent) {}

[J.Hilk]

@HenkCoder the error message is really self-explanatory:

qobject_cast requires the type to have a Q_OBJECT macro

you didn't add the Q_OBJECT macro in your header file.

---

but assuming, your TextEdit is derived from QWidget, somewhere and you placed it via the designer, than yes, the cast should work, if you place the macro

[VRonin]

Or you maybe forgot a Q? qobject_cast<QTextEdit*>?

[HenkCoder]

@VRonin No, I inherited QTextEdit class.

[HenkCoder]

@J-Hilk
Hi, actually, no.
I just have a blank tabWidget and in the Mainwindow constructor it creates a tab with the textEdit in it.
Btw TextEdit is derived from QTextEdit.
How do I make the thing with Q_OBJECT macro then?
This is the code in the header:

class TextEdit : public QTextEdit
{
public:
    bool canInsertFromMimeData(const QMimeData* source) const
    {
        return source->hasImage() || source->hasUrls() ||
            QTextEdit::canInsertFromMimeData(source);
    }

    void insertFromMimeData(const QMimeData* source)
    {
        if (source->hasImage())
        {
            static int i = 1;
            QUrl url(QString("dropped_image_%1").arg(i++));
            dropImage(url, qvariant_cast<QImage>(source->imageData()));
        }
        else if (source->hasUrls())
        {
            foreach (QUrl url, source->urls())
            {
                QFileInfo info(url.toLocalFile());
                if (QImageReader::supportedImageFormats().contains(info.suffix().toLower().toLatin1()))
                    dropImage(url, QImage(info.filePath()));
                else
                    dropTextFile(url);
            }
        }
        else
        {
            QTextEdit::insertFromMimeData(source);
        }
    }

private:
    void dropImage(const QUrl& url, const QImage& image)
    {
        if (!image.isNull())
        {
            document()->addResource(QTextDocument::ImageResource, url, image);
            textCursor().insertImage(url.toString());
        }
    }

    void dropTextFile(const QUrl& url)
    {
        QFile file(url.toLocalFile());
        if (file.open(QIODevice::ReadOnly | QIODevice::Text))
            textCursor().insertText(file.readAll());
    }
};

Hope it helps.

[VRonin]

@HenkCoder said in How to use qobject_cast with inherited class:

class TextEdit : public QTextEdit
{
public:

class TextEdit : public QTextEdit
{
Q_OBJECT
public:
using QTextEdit::QTextEdit; // this is unrelated but forwards the constructor of QTextEdit

[J.Hilk]

@HenkCoder said in How to use qobject_cast with inherited class:

How do I make the thing with Q_OBJECT macro then?

class TextEdit : public QTextEdit
{
    Q_OBJECT
public:

and since we're at it, lets do a proper constructor for a Qt class as well:

public:
   explicit TextEdit(QWidget *parent = nullptr) : QTextEdit(parent) {}

[HenkCoder]

Thanks guys! it worked