Archived:Creating a custom custom line editor from QLineEdit

Article Metadata

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Tested with

Devices(s): Emulator

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Compatibility

Platform(s): S60 5th Edition

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Article

Keywords: QLineEdit

Created: (21 Nov 2010)

Last edited: somnathbanik (08 Jun 2011)

This example shows how to derive our own Line Widget from QLineEdit. The QLineEdit widget 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.

Prerequisites

• Qt 4.6.2 or above (tested ok with 4.7 too) Nokia Qt SDK with latest Update will do just fine
• A Qt & Data enabled device [Optional] we will use Qt Nokia SDK's Simulator.

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 {{Icode|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 for example

    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

• More on QLineEdit
• SDK

--skumar_rao 09:27, 21 November 2010 (UTC)