Golang with Qt issue with painting in paintEvent

Question

I'm using this Golang Qt binding here to create a simple code editor. I'm connecting a paintEvent callback handler to the actual editor, in which I'm trying to do the painting. As I've found in various forums this is the only point when the painting should be done. However, when calling painter := gui.NewQPainter2(ce.editor) I receive some warning outputs

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1

and when calling the setPen function I get the message

QPainter::setPen: Painter not active

Here is a working example of the issue

package main


import (
    "os"

    "github.com/therecipe/qt/widgets"
    "github.com/therecipe/qt/gui"
    "github.com/therecipe/qt/core"
)

type CodeEditor struct {
    editor *widgets.QPlainTextEdit
}

func NewCodeEditor(parent *widgets.QWidget) *CodeEditor {
    codeEditor := &CodeEditor{editor: widgets.NewQPlainTextEdit(parent)}
    codeEditor.setupSignals()
    return codeEditor
}

func (ce *CodeEditor) setupSignals() {
    ce.editor.ConnectPaintEvent(ce.paintEvent)
}

func (ce *CodeEditor) paintEvent(event *gui.QPaintEvent) {
    painter := gui.NewQPainter2(ce.editor)
    color := gui.NewQColor6("red")
    painter.SetPen2(color)
    painter.DestroyQPainter()
}

func main() {
    core.QCoreApplication_SetAttribute(core.Qt__AA_ShareOpenGLContexts, true)
    widgets.NewQApplication(len(os.Args), os.Args)

    mainWindow := widgets.NewQMainWindow(nil, 0)
    codeEditor := NewCodeEditor(nil)

    mainWindow.SetCentralWidget(codeEditor.editor)
    mainWindow.ShowMaximized()

    widgets.QApplication_Exec()
}

Answer 1

You have not activated the QPainter instance. Check https://doc.qt.io/qt-5/qpainter.html#begin