QT4.8 - Implement highlight to QLineEdit - c++

Question

I am looking for a way to implement a highlighter for the QLineEdit widget.
I am using a QLineEdit to store a a path variable in my application, and I would to highlight environment variables.
Something like this:
${MY_ENVVAR}/foo/bar/myfile
Practically I would to have something like the QHightligher class.

Answer 1

Subclass QSyntaxHighliger
Write your own highlightBlock() method
Detect in your string this specific text which must be colored (you can do this for example by regular expression QRegExp) and use setFormat() method to paint string from x to x+n with some color
Helpful link: http://qt-project.org/doc/qt-4.8/qsyntaxhighlighter.html#highlightBlock
I never used highliter with QLineEdit before, so it can be impossible. But we can simply attach highliter to the QTextEdit. So we should create lineEdit from textEdit, there are many examples in web how to do that.
For example (I use code given by hyde with small additions.)
TextEdit.h
#ifndef TEXTEDIT_H
#define TEXTEDIT_H
#include <QTextEdit>
#include <QCompleter>
#include <QTextEdit>
#include <QKeyEvent>
#include <QStyleOption>
#include <QApplication>
class TextEdit : public QTextEdit
{
Q_OBJECT
public:
explicit TextEdit(QWidget *parent = 0)
{
setTabChangesFocus(true);
setWordWrapMode(QTextOption::NoWrap);
setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
setFixedHeight(sizeHint().height());
}
void keyPressEvent(QKeyEvent *event)
{
if (event->key() == Qt::Key_Return || event->key() == Qt::Key_Enter)
event->ignore();
else
QTextEdit::keyPressEvent(event);
}
QSize sizeHint() const
{
QFontMetrics fm(font());
int h = qMax(fm.height(), 14) + 4;
int w = fm.width(QLatin1Char('x')) * 17 + 4;
QStyleOptionFrameV2 opt;
opt.initFrom(this);
return (style()->sizeFromContents(QStyle::CT_LineEdit, &opt, QSize(w, h).
expandedTo(QApplication::globalStrut()), this));
}
};
#endif // TEXTEDIT_H
Usage (in the main.cpp)
#include "textedit.h"
//...
TextEdit *t = new TextEdit;
t->show();
new Highlighter(t->document());
Highlighter constructor as example
Highlighter::Highlighter(QTextDocument *parent)
: QSyntaxHighlighter(parent)
{
}