Development/Tutorials/Saving and loading (ko)

Development/Tutorials/Saving_and_loading

파일 로드하고 저장하기

Tutorial Series	Beginner Tutorial
Previous	Tutorial 3 - KActions
What's Next	Tutorial 5 - KCmdLineArgs 사용하기
Further Reading	KIO::NetAccess QFile

개요

이제 기본적인 텍스트 에디터 인터페이스를 가지게 되었다. 이제는 이것을 좀 더 유용하게 만들 시간이다. 가장 기본적으로 텍스트 에디터는 디스트에서 파일을 로드하고, 당식이 생성했거나 수정한 파일에 저장하거나 파일을 새롭게 생성하도록 할 필요가 있다.

Now that we have a basic text editor interface, it's time to make it do something useful. At the most basic, a text editor needs to be able to load files from disc, save files that you've created/edited and create new files.

KDE는 개발자가 좀 더 나은 삶을 위하여 파일을 다루기 위한 많은 클래스를 제공한다. KIO 라이브러리는 표준 다이얼로그와 같은 투명한 네트워크를 통해 파일을 쉽게 접근할 수 있도록 해준다.

KDE provides a number of classes for working with files which make life a lot easier for developers. The KIO library allows you to easily access files through network-transparent protocols as well as providing standard file dialogs.

코드

main.cpp

include <KApplication>
include <KAboutData>
include <KCmdLineArgs>

include "mainwindow.h"

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

 KAboutData aboutData( "tutorial4", "tutorial4",
     ki18n("Tutorial 4"), "1.0",
     ki18n("A simple text area which can load and save."),
     KAboutData::License_GPL,
     ki18n("Copyright (c) 2007 Developer") );
 KCmdLineArgs::init( argc, argv, &aboutData );
 KApplication app;

 MainWindow* window = new MainWindow();
 window->show();
 return app.exec();

} main.cpp는 tutrial 3를 tutrial4로 변경한 것을 제외하고는 튜트리얼3에서 변경된 점이 없다.

main.cpp hasn't changed from tutorial 3 except to change any reference to tutorial 3 to tutorial 4.

mainwindow.h

ifndef MAINWINDOW_H
define MAINWINDOW_H

include <KXmlGuiWindow>
include <KTextEdit>

class MainWindow : public KXmlGuiWindow
{

 Q_OBJECT //new from tutorial3
 
 public:
   MainWindow(QWidget *parent=0);
 
 private:
   KTextEdit* textArea;
   void setupActions();
   QString fileName; //new

 private slots: //new
   void newFile(); //new
   void openFile(); //new
   void saveFile(); //new
   void saveFileAs(); //new
   void saveFileAs(const QString &outputFileName); //new

};

endif

파일을 로드하고, 저장하는 기능을 추가하려면, 그러한 일을 하는 함수를 만들어야 한다. Qt의 시그널/슬롯 메커니즘을 통해 함수가 호출되기 위해, 19번째 줄에서 수행할 슬롯으로 이러한 함수들을 정의해야 한다. 이 헤더 파일에 있는 슬롯을 사용하는 중이라면, Q_OBJECT 매크로를 추가해야 한다.

Since we want to add the ability to load and save files, we must add the functions which will do the work. Since the functions will be called through Qt's signal/slot mechanism we must specify that these functions are slots as we do on line 19. Since we are using slots in this header file, we must also add the Q_OBJECT macro.

또한 우리는 현재 열린 파일의 파일 이름의 흔적을 유지하기를 원하므로, QString fileName을 선언하였다.

We also want to keep track of the filename of the currently opened file so we declare a QString fileName.

mainwindow.cpp

include "mainwindow.h"

include <KApplication>
include <KAction>
include <KLocale>
include <KActionCollection>
include <KStandardAction>
include <KFileDialog> //new
include <KMessageBox> //new
include <KIO/NetAccess> //new
include <KSaveFile> //new
include <QTextStream> //new

MainWindow::MainWindow(QWidget *parent)

   : KXmlGuiWindow(parent),
     fileName(QString()) //new

 textArea = new KTextEdit;
 setCentralWidget(textArea);

 setupActions();

}
void MainWindow::setupActions()
{

 KAction* clearAction = new KAction(this);
 clearAction->setText(i18n("Clear"));
 clearAction->setIcon(KIcon("document-new"));
 clearAction->setShortcut(Qt::CTRL + Qt::Key_W);
 actionCollection()->addAction("clear", clearAction);
 connect(clearAction, SIGNAL(triggered(bool)),
         textArea, SLOT(clear()));

 KStandardAction::quit(kapp, SLOT(quit()),
                       actionCollection());

 KStandardAction::open(this, SLOT(openFile()),
                       actionCollection()); //new

 KStandardAction::save(this, SLOT(saveFile()),
                       actionCollection()); //new

 KStandardAction::saveAs(this, SLOT(saveFileAs()),
                       actionCollection()); //new

 KStandardAction::openNew(this, SLOT(newFile()),
                       actionCollection()); //new

 setupGUI();

}
//New from here on
void MainWindow::newFile()
{

 fileName.clear();
 textArea->clear();

}
void MainWindow::saveFileAs(const QString &outputFileName)
{

 KSaveFile file(outputFileName);
 file.open();
 
 QByteArray outputByteArray;
 outputByteArray.append(textArea->toPlainText());
 file.write(outputByteArray);
 file.finalize();
 file.close();
 
 fileName = outputFileName;

}
void MainWindow::saveFileAs()
{

 saveFileAs(KFileDialog::getSaveFileName());

}
void MainWindow::saveFile()
{

 if(!fileName.isEmpty())
 {
   saveFileAs(fileName);
 }
 else
 {
   saveFileAs();
 }

}
void MainWindow::openFile()
{

 QString fileNameFromDialog = KFileDialog::getOpenFileName();

 QString tmpFile;
 if(KIO::NetAccess::download(fileNameFromDialog, tmpFile, 
        this))
 {
   QFile file(tmpFile);
   file.open(QIODevice::ReadOnly);
   textArea->setPlainText(QTextStream(&file).readAll());
   fileName = fileNameFromDialog;

   KIO::NetAccess::removeTempFile(tmpFile);
 }
 else
 {
   KMessageBox::error(this, 
       KIO::NetAccess::lastErrorString());
 }

}

tutorial4ui.rc

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE kpartgui SYSTEM "kpartgui.dtd"> <gui name="tutorial4" version="1">

 <ToolBar name="mainToolBar" >
   <text>Main Toolbar</text>
   <Action name="clear" />
 </ToolBar>
 <MenuBar>
   <Menu name="file" >
     <Action name="clear" />
   </Menu>
 </MenuBar>

</gui>

name이 'tutorial4'로 바뀐 것을 제외하고 tutrial 3의 tutorial3ui.rc과 동일하다. 우리는 KStandardAction에 대한 어떤 정보도 넣을 필요가 없다. 이 액션의 배치들은 KDE에 의해서 자동적으로 다루어지기 때문이다.

This is identical to tutorial3ui.rc from tutorial 3 except the name has changed to 'tutorial4'. We do not need to add any information about any of the KStandardActions since the placement of those actions is handled automatically by KDE.

설명

자, 이제 로드하거나 저장하기를 수행할 코드를 구현한다. 이것은 mainwindow.cpp에서 모든 것이 일어날 것이다.

Okay, now to implement the code that will do the loading and saving. This will all be happening in mainwindow.cpp

우리가 할 첫번째 일은

The first thing we do is add

fileName(QString()) 위의 코드를 16번째 줄인 MainWindow 생성자 리스트에 추가하는 것이다. 이것은 시작할 때 fileName이 비어 있도록 해준다.

to the MainWindow constructor list on line 16. This makes sure that fileName is empty right from the beginning.

액션 추가하기

The first thing we are going to do is provide the outward interface for the user so they can tell the application to load and save. Like with the quit action in tutorial 3, we will use KStandardActions. On lines 37 to 47 we add the actions in the same way as for the quit action. For each one, we connect it to the appropriate slot that we declared in the header file.

Creating a new document

The first function we create is the newFile() function. void MainWindow::newFile() {

 fileName.clear();
 textArea->clear();

} fileName.clear() sets the fileName QString to be empty to reflect the fact that this document does not yet have a presence on disc. textArea->clear() then clears the central text area using the same function that we connected the clear KAction to in tutorial 3.

Saving a file

saveFileAs(QString)

Now we get onto our first file handling code. We're going to implement a function which will save the contents of the text area to the file name given as a parameter. KDE provides a class for safely saving a file called KSaveFile which is derived from Qt's QFile.

The function's prototype is void MainWindow::saveFileAs(const QString &outputFileName)

We then create our KSaveFile object and open it with KSaveFile file(outputFileName); file.open();

Now that we have our file to write to, we need to format the text in the text area to a format which can be written to file. For this, we create a QByteArray and fill it with the plain text version of whatever is in the text area: QByteArray outputByteArray; outputByteArray.append(textArea->toPlainText()); Now that we have our QByteArray, we use it to write to the file with KSaveFile::write(). If we were using a normal QFile, this would make the changes immediately. However, if a problem occurred partway through writing, the file would become corrupted. For this reason, KSaveFile works by first writing to a temporary file and then, when you call KSaveFile::finalize() the changes are made to the actual file. file.write(outputByteArray); file.finalize(); file.close(); Finally, we set MainWindows's fileName member to point to the file name we just saved to. fileName = outputFileName;

saveFileAs()

This is the function that the saveAs slot is connected to. It simply calls the generic saveFileAs(QString) function and passes the file name returned by KFileDialog::getSaveFileName().

void MainWindow::saveFileAs() {

 saveFileAs(KFileDialog::getSaveFileName());

}

This our first actual use of the KIO library. KFileDialog provides a number of static functions for displaying the common file dialog that is used by all KDE applications. Calling KFileDialog::getSaveFileName() will display a dialog where the user can select the name of the file to save to or choose a new name. The function returns the full file name, which we then pass to saveFileAs(QString).

saveFile()

void MainWindow::saveFile() {

 if(!fileName.isEmpty())
 {
   saveFileAs(fileName);
 }
 else
 {
   saveFileAs();
 }

}

There's nothing exciting or new in this function, just the logic to decide whether or not to show the save dialog. If fileName is not empty, then the file is saved to fileName. But if it is, then the dialog is shown to allow the user to select a file name.

Loading a file

Finally, we get round to being able to load a file from disc. The code for this is all contained in MainWindow::openFile().

First we must ask the user for the name of the file they wish to open. We do this using another one of the KFileDialog functions, this time getOpenFileName(): QString fileNameFromDialog = KFileDialog::getOpenFileName();

Then we use the KIO library to retrieve our file. This allows us to open the file with QFile even if it's stored in a remote location like an FTP site. We make the following call to NetAccess's download() function KIO::NetAccess::download(fileNameFromDialog, tmpFile, this) The first argument is the name of the file you wish to download. The second is a QString which, after the download is complete, will contain the location of the temporary copy of the file. It is this tmpFile we will work with from now on.

The function returns true or false depending on whether the transfer was successful. If it failed, we display a message box giving the error: KMessageBox::error(this, KIO::NetAccess::lastErrorString());

Otherwise, we continue with opening the file.

We create a QFile by passing the temporary file created by NetAccess::download() to its constructor and then open it in read-only mode QFile file(tmpFile); file.open(QIODevice::ReadOnly);

In order to display the contents of the file, we must use a QTextStream. We create one by passing the contents of our file to its constructor and then call QFile's readAll() function to get the text from the file. This is then passed to the setPlainText() function of our text area.

textArea->setPlainText(QTextStream(&file).readAll());

We then store the path of the file we just opened: fileName = fileNameFromDialog; and finally, we remove the temporary file that was created by NetAccess::download(): KIO::NetAccess::removeTempFile(tmpFile);

Make, Install And Run

CMakeLists.txt

project(tutorial4)

find_package(KDE4 REQUIRED) include_directories(${KDE4_INCLUDES})

set(tutorial4_SRCS

 main.cpp
 mainwindow.cpp

)
kde4_add_executable(tutorial4 ${tutorial4_SRCS})
target_link_libraries(tutorial4 ${KDE4_KDEUI_LIBS}

                               ${KDE4_KIO_LIBS})

install(TARGETS tutorial4 DESTINATION ${BIN_INSTALL_DIR})
install(FILES tutorial4ui.rc

       DESTINATION ${DATA_INSTALL_DIR}/tutorial4)

Since we are now using the KIO library, we must tell CMake to link against it. We do this by passing ${KDE4_KIO_LIBS} to the target_link_libraries() function.

With this file, the tutorial can built and run in the same way as tutorial 3. For more information, see tutorial 3.

mkdir build && cd build
cmake .. -DCMAKE_INSTALL_PREFIX=$HOME
make install
$HOME/bin/tutorial4

Moving On

Now you can move on to the KCmdLineArgs tutorial.