How to place an icon onto a QLineEdit?

Question

There is a Search field with the magnification-lens and a greyed out \"search\" keyword at the top right corner of stackoverflow.com web site:

Answer 1

To have a result like this:

You can subclass the QLineEdit.
So your header should look something like this:

#ifndef LINEEDITICON_H
#define LINEEDITICON_H

#include <QLineEdit>
#include <QIcon>

class LineEditIcon : public QLineEdit
{
    Q_OBJECT

public:
    LineEditIcon(const QIcon icon, QWidget *parent = Q_NULLPTR);
    ~LineEditIcon();
    void setIcon(QIcon icon);    
protected:
    virtual void paintEvent(QPaintEvent *event);    
private:
    QIcon m_icon;       
};

#endif // LINEEDITICON_H

And your source file look like:

#include "lineediticon.h"
#include <QPainter>

LineEditIcon::LineEditIcon(const QIcon icon, QWidget *parent)
    : QLineEdit(parent)
{
    setIcon(icon);
}

LineEditIcon::~LineEditIcon()
{    
}

void LineEditIcon::setIcon(QIcon icon)
{
    m_icon = icon;
    if (m_icon.isNull())
        setTextMargins(1, 1, 1, 1);
    else
        setTextMargins(20, 1, 1, 1);
}

void LineEditIcon::paintEvent(QPaintEvent * event)
{
    QLineEdit::paintEvent(event);
    if (!m_icon.isNull()) {
        QPainter painter(this);
        QPixmap pxm = m_icon.pixmap(height() - 6, height() - 6);
        int x = 2, cx = pxm.width();

        painter.drawPixmap(x, 3, pxm);
        painter.setPen(QColor("lightgrey"));
        painter.drawLine(cx + 2, 3, cx + 2, height() - 4);
    }
}

Edit: A possible solution is to use a custom plugin to use it directly in QtDesigner.