(C++) QUndoCommand example 1

QUndoCommand example 1 is a QUndoCommand example.

Technical facts

Application type(s)

Desktop application

Operating system(s) or programming environment(s)

Lubuntu 12.10 (quantal)

IDE(s):

Qt Creator 2.5.2

Project type:

GUI application

C++ standard:

C++98

Compiler(s):

G++ 4.7.2

Libraries used:

Qt: version 4.8.3 (32 bit)
STL: GNU ISO C++ Library, version 4.7.2

Qt project file: CppQUndoCommandExample1.pro


#-------------------------------------------------

#

# Project created by QtCreator 2013-04-21T19:59:08

#

#-------------------------------------------------



QT       += core gui



greaterThan(QT_MAJOR_VERSION, 4): QT += widgets



TARGET = CppQUndoCommandExample1

TEMPLATE = app





SOURCES += main.cpp\

        qtdialog.cpp \

    qtbuttonincrementcommand.cpp



HEADERS  += qtdialog.h \

    qtbuttonincrementcommand.h



FORMS    += qtdialog.ui

main.cpp


#include <QApplication>

#include "qtdialog.h"



int main(int argc, char *argv[])

{

  QApplication a(argc, argv);

  QtDialog w;

  w.show();

  

  return a.exec();

}

qtbuttonincrementcommand.h


#ifndef QTBUTTONINCREMENTCOMMAND_H

#define QTBUTTONINCREMENTCOMMAND_H



#include <QUndoCommand>



struct QPushButton;



struct QtButtonIncrementCommand : public QUndoCommand

{

  explicit QtButtonIncrementCommand(QPushButton * const button);



  ///Virtual function supplied by QUndoCommand

  void redo();



  ///Virtual function supplied by QUndoCommand

  void undo();



  private:

  QPushButton * const m_button;



};



#endif // QTBUTTONINCREMENTCOMMAND_H

qtbuttonincrementcommand.cpp


#include "qtbuttonincrementcommand.h"



#include <cassert>

#include <QPushButton>



QtButtonIncrementCommand::QtButtonIncrementCommand(

  QPushButton * const button)

  : m_button(button)

{

  assert(m_button);

}



void QtButtonIncrementCommand::redo()

{

  const int current_number = m_button->text().toInt();

  const int new_number = current_number + 1;

  m_button->setText(QString::number(new_number) );

}



void QtButtonIncrementCommand::undo()

{

  const int current_number = m_button->text().toInt();

  const int new_number = current_number - 1;

  m_button->setText(QString::number(new_number) );

}

qtdialog.h


#ifndef QTDIALOG_H

#define QTDIALOG_H



#include <QDialog>



namespace Ui {

  class QtDialog;

}



struct QUndoStack;



class QtDialog : public QDialog

{

  Q_OBJECT

  

public:

  explicit QtDialog(QWidget *parent = 0);

  ~QtDialog();





  

private slots:

  void keyPressEvent(QKeyEvent *);

  void on_button_clicked();



private:

  Ui::QtDialog *ui;



  QUndoStack * const m_stack;

};



#endif // QTDIALOG_H

qtdialog.cpp


#include "qtdialog.h"



#include <QKeyEvent>

#include <QUndoStack>

#include "qtbuttonincrementcommand.h"



#include "ui_qtdialog.h"



QtDialog::QtDialog(QWidget *parent) :

  QDialog(parent),

  ui(new Ui::QtDialog),

  m_stack(new QUndoStack(this))

{

  ui->setupUi(this);

}



QtDialog::~QtDialog()

{

  delete ui;

}



void QtDialog::keyPressEvent(QKeyEvent * e)

{

  if ( (e->modifiers() & Qt::ControlModifier)

    && !(e->modifiers() & Qt::ShiftModifier)

    && e->key() == Qt::Key_Z)

  {

    m_stack->undo();

  }

  if ( (e->modifiers() & Qt::ControlModifier)

    && (e->modifiers() & Qt::ShiftModifier)

    && e->key() == Qt::Key_Z)

  {

    m_stack->redo();

  }

}



void QtDialog::on_button_clicked()

{

  QtButtonIncrementCommand * const cmd

    = new QtButtonIncrementCommand(ui->button);



  //By pushing the command, redo is called

  m_stack->push(cmd);

}

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