Unable to use drawContents inside a QTextEdit

anphetamina

I have a class that include a reference to a QTextEdit and a QPainter object initialized as following:

class MyClass : QObject {

QWidget &parent;
Ui::MainWindow &ui;
QPaint painter;
...
}

MyClass::MyClass() : painter(ui.textEdit) {

connect(ui.textEdit, &QTextEdit::cursorPositionChanged, this, &MyClass::cursorPositionChanged);
painter.setPen(Qt::yellow);

}

And this is the slot connected to the signal:

void MyClass::cursorPositionChanged() {
    QRect cursorRect = ui.textEdit->cursorRect();
    painter.drawRect(cursorRect);
    ui.textEdit->document()->drawContents(&painter);
}

Once I move the cursor inside the QTextEdit document the output is:

QPainter::drawRects: Painter not active
QPainter::save: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::pen: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QPainter::setPen: Painter not active
QPainter::restore: Unbalanced save/restore

and it doesn't paint anything in the document. What I'm missing?

SGaist

Hi,

You can't paint on a widget in an arbitrary manner like you do. And you can't paint on a widget from an arbitrary source either.

What exactly do you want to achieve ?

anphetamina

I need to paint the current cursor in the document

Bonnie

[EDITED]
A QPainter must be begin()ed / constructed with a QPaintDevice to use.
And if the device is a widget, then it need to be begin()ed / constructed and used only in its paintEvent.
So if drawContents is not called in a widget's paintEvent, it is usually used to draw the document to another QPaintDevice, like an image or a pdf.
Here I even don't know what do you want to paint on since you never set any QPaintDevice to the painter.

SGaist

@anphetamina said in Unable to use drawContents inside a QTextEdit:

I need to paint the current cursor in the document

QTextEdit already draws the cursor where it is so that's a bit strange. Can you give more details ?

anphetamina

@SGaist I need to paint a line on the document cursor using a specified color

anphetamina

@SGaist overriding paintEvent from QTextEdit I successfully painted a vertical line in the cursor position but I need to draw more lines on demand, is that possible?

SGaist

What do you mean by on demands ?
What kind of line ?

Christian Ehrlicher

@anphetamina said in Unable to use drawContents inside a QTextEdit:

but I need to draw more lines on demand, is that possible?

Then draw more lines in paintEvent() ...