Archived:Creating a custom custom line editor from QLineEdit

This example shows how to derive our own Line Widget from QLineEdit. QLineEdit is a one-line text editor. A line edit allows the user to enter and edit a single line of plain text with a useful collection of editing functions, including undo and redo, cut and paste, and drag and drop.

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Qt Quick should be used for all UI development on mobile devices. The approach described in this article (based on C++ for the Qt UI) deprecated.

Article Metadata

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Tested with

SDK: Qt 4.6.2, Qt 4.7

Devices(s): Emulator

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Compatibility

Platform(s): S60 5th Edition

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Article

Keywords: QLineEdit

Created: skumar_rao (21 Nov 2010)

Last edited: hamishwillee (02 Mar 2012)

Implementation

We will derive a class named QCustomEditLine

class QCustomEditLine : public QLineEdit
 
QCustomEditLine::QCustomEditLine(QWidget *parent) : QLineEdit(parent)

Add a function to take the default text once we get it we will refresh the control to re-draw.

emptyMessage = msg;
drawEmptyMsg = text().isEmpty();
update();

Derive paintEvent( QPaintEvent *ev ) to draw the text that we want to show when there is no text is entered.

QPainter p(this);
QFont f = font();
f.setItalic(true);
p.setFont(f);
 
QColor color(palette().color(foregroundRole()));
color.setAlphaF(0.5);
p.setPen(color);
 
QStyleOptionFrame opt;
initStyleOption(&opt);
QRect cr = style()->subElementRect(QStyle::SE_LineEditContents, &opt, this);
cr.setLeft(cr.left() + 2);
cr.setRight(cr.right() - 2);
 
p.drawText(cr, Qt::AlignLeft|Qt::AlignVCenter, emptyMessage);

control the drawing to show the default text when control is focused out and blank it when cointrol focused in.

Now we are ready to add to our widget. To use do the following:

m_lineout = new QCustomEditLine(this);
m_lineout->setEmptyMessage("Enter you Email Address");

qcustomeditline.h

#ifndef QCUSTOMEDITLINE_H
#define QCUSTOMEDITLINE_H
 
#include <QtGui>
 
class QCustomEditLine : public QLineEdit
{
    Q_OBJECT
public:
    QCustomEditLine(QWidget *parent = 0);
    virtual ~QCustomEditLine();
 
public:
    void setEmptyMessage( const QString &msg );
 
protected:
    void paintEvent( QPaintEvent *ev );
    void focusInEvent( QFocusEvent *ev );
    void focusOutEvent( QFocusEvent *ev );
 
private:
    QString emptyMessage;
    bool drawEmptyMsg;
};
 
#endif // QCUSTOMEDITLINE_H

qcustomeditline.cpp

#include "qcustomeditline.h"
 
QCustomEditLine::QCustomEditLine(QWidget *parent)
                : QLineEdit( parent ){
 
 
}
 
QCustomEditLine::~QCustomEditLine() {
 
}
 
void QCustomEditLine::setEmptyMessage( const QString &msg ) {
    emptyMessage = msg;
    drawEmptyMsg = text().isEmpty();
    update();
}
 
void QCustomEditLine::paintEvent( QPaintEvent *ev ) {
    QLineEdit::paintEvent( ev );
 
    if ( text().isEmpty() ) {
        QPainter p(this);
        QFont f = font();
        f.setItalic(true);
        p.setFont(f);
 
        QColor color(palette().color(foregroundRole()));
        color.setAlphaF(0.5);
        p.setPen(color);
 
        QStyleOptionFrame opt;
        initStyleOption(&opt);
        QRect cr = style()->subElementRect(QStyle::SE_LineEditContents, &opt, this);
        cr.setLeft(cr.left() + 2);
        cr.setRight(cr.right() - 2);
 
        p.drawText(cr, Qt::AlignLeft|Qt::AlignVCenter, emptyMessage);
    }
}
 
void QCustomEditLine::focusInEvent( QFocusEvent *ev ) {
    if ( drawEmptyMsg ) {
        drawEmptyMsg = false;
        update();
    }
    QLineEdit::focusInEvent( ev );
}
 
void QCustomEditLine::focusOutEvent( QFocusEvent *ev ) {
    if ( text().isEmpty() ) {
        drawEmptyMsg = true;
        update();
    }
    QLineEdit::focusOutEvent( ev );
}

Reference

• QLineEdit