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| {{Template:I18n/Language Navigation Bar (zh_CN)|Development/Tutorials/Saving_and_loading}} | | {{Template:I18n/Language Navigation Bar|Development/Tutorials/Saving_and_loading}} |
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| {{TutorialBrowser (zh_CN)| | | {{TutorialBrowser| |
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| series=初学者教程| | | series=初学者教程| |
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| name=保存与载入文件| | | name=教程4 - 保存与装载| |
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| pre=[[Development/Tutorials/Using_KActions (zh_CN)|教程3 - KActions]]| | | pre=[[Development/Tutorials/Using_KActions|教程3 - KActions]]| |
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| next=[[Development/Tutorials/KCmdLineArgs (zh_CN)|教程5 - 使用KCmdLineArgs]]| | | next=[[Development/Tutorials/KCmdLineArgs|教程5 - 使用KCmdLineArgs]]| |
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| reading=KIO::{{class|NetAccess}} {{qt|QFile}} | | reading=KIO::{{class|NetAccess}} {{qt|QFile}} |
| }} | | }} |
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| ==Abstract==
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|
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| 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.
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|
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| 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.
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|
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| [[image:introtokdetutorial4.png|frame|center]]
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|
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| == The Code ==
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|
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| ===main.cpp===
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| <code cppqt n>
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| #include <KApplication>
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| #include <KAboutData>
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| #include <KCmdLineArgs>
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|
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| #include "mainwindow.h"
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|
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| int main (int argc, char *argv[])
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| {
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| KAboutData aboutData( "tutorial4", "tutorial4",
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| ki18n("Tutorial 4"), "1.0",
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| ki18n("A simple text area which can load and save."),
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| KAboutData::License_GPL,
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| ki18n("Copyright (c) 2007 Developer") );
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| KCmdLineArgs::init( argc, argv, &aboutData );
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| KApplication app;
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|
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| MainWindow* window = new MainWindow();
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| window->show();
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| return app.exec();
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| }
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| </code>
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| <tt>main.cpp</tt> hasn't changed from tutorial 3 except to change any reference to tutorial 3 to tutorial 4.
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|
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| ===mainwindow.h===
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| <code cppqt n>
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| #ifndef MAINWINDOW_H
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| #define MAINWINDOW_H
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|
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| #include <KXmlGuiWindow>
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| #include <KTextEdit>
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|
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| class MainWindow : public KXmlGuiWindow
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| {
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| Q_OBJECT //new from tutorial3
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|
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| public:
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| MainWindow(QWidget *parent=0);
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|
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| private:
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| KTextEdit* textArea;
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| void setupActions();
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| QString fileName; //new
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|
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| private slots: //new
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| void newFile(); //new
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| void openFile(); //new
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| void saveFile(); //new
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| void saveFileAs(); //new
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| void saveFileAs(const QString &outputFileName); //new
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| };
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|
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| #endif
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| </code>
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| 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 [http://doc.trolltech.com/latest/signalsandslots.html 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 [http://doc.trolltech.com/latest/qobject.html#Q_OBJECT <tt>Q_OBJECT</tt>] macro.
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|
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| We also want to keep track of the filename of the currently opened file so we declare a <tt>{{qt|QString}} fileName</tt>.
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|
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| ===mainwindow.cpp===
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| <code cppqt n>
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| #include "mainwindow.h"
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|
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| #include <KApplication>
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| #include <KAction>
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| #include <KLocale>
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| #include <KActionCollection>
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| #include <KStandardAction>
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| #include <KFileDialog> //new
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| #include <KMessageBox> //new
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| #include <KIO/NetAccess> //new
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| #include <KSaveFile> //new
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| #include <QTextStream> //new
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|
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| MainWindow::MainWindow(QWidget *parent)
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| : KXmlGuiWindow(parent),
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| fileName(QString()) //new
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| {
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| textArea = new KTextEdit;
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| setCentralWidget(textArea);
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|
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| setupActions();
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| }
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|
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| void MainWindow::setupActions()
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| {
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| KAction* clearAction = new KAction(this);
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| clearAction->setText(i18n("Clear"));
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| clearAction->setIcon(KIcon("document-new"));
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| clearAction->setShortcut(Qt::CTRL + Qt::Key_W);
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| actionCollection()->addAction("clear", clearAction);
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| connect(clearAction, SIGNAL(triggered(bool)),
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| textArea, SLOT(clear()));
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|
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| KStandardAction::quit(kapp, SLOT(quit()),
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| actionCollection());
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|
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| KStandardAction::open(this, SLOT(openFile()),
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| actionCollection()); //new
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|
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| KStandardAction::save(this, SLOT(saveFile()),
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| actionCollection()); //new
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|
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| KStandardAction::saveAs(this, SLOT(saveFileAs()),
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| actionCollection()); //new
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|
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| KStandardAction::openNew(this, SLOT(newFile()),
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| actionCollection()); //new
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|
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| setupGUI();
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| }
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|
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| //New from here on
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|
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| void MainWindow::newFile()
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| {
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| fileName.clear();
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| textArea->clear();
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| }
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|
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| void MainWindow::saveFileAs(const QString &outputFileName)
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| {
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| KSaveFile file(outputFileName);
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| file.open();
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|
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| QByteArray outputByteArray;
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| outputByteArray.append(textArea->toPlainText().toUtf8());
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| file.write(outputByteArray);
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| file.finalize();
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| file.close();
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|
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| fileName = outputFileName;
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| }
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|
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| void MainWindow::saveFileAs()
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| {
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| saveFileAs(KFileDialog::getSaveFileName());
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| }
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|
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| void MainWindow::saveFile()
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| {
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| if(!fileName.isEmpty())
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| {
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| saveFileAs(fileName);
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| }
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| else
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| {
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| saveFileAs();
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| }
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| }
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|
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| void MainWindow::openFile()
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| {
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| QString fileNameFromDialog = KFileDialog::getOpenFileName();
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|
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| QString tmpFile;
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| if(KIO::NetAccess::download(fileNameFromDialog, tmpFile,
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| this))
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| {
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| QFile file(tmpFile);
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| file.open(QIODevice::ReadOnly);
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| textArea->setPlainText(QTextStream(&file).readAll());
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| fileName = fileNameFromDialog;
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|
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| KIO::NetAccess::removeTempFile(tmpFile);
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| }
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| else
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| {
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| KMessageBox::error(this,
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| KIO::NetAccess::lastErrorString());
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| }
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| }
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| </code>
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|
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| ===tutorial4ui.rc===
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| <code xml n>
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| <?xml version="1.0" encoding="UTF-8"?>
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| <!DOCTYPE kpartgui SYSTEM "kpartgui.dtd">
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| <gui name="tutorial4" version="1">
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| <ToolBar name="mainToolBar" >
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| <text>Main Toolbar</text>
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| <Action name="clear" />
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| </ToolBar>
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| <MenuBar>
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| <Menu name="file" >
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| <Action name="clear" />
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| </Menu>
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| </MenuBar>
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| </gui>
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| </code>
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| This is identical to <tt>tutorial3ui.rc</tt> from tutorial 3 except the <tt>name</tt> has changed to 'tutorial4'. We do not need to add any information about any of the <tt>KStandardAction</tt>s since the placement of those actions is handled automatically by KDE.
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|
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| ==Explanation==
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|
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| Okay, now to implement the code that will do the loading and saving. This will all be happening in <tt>mainwindow.cpp</tt>
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|
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| The first thing we do is add
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| <code cppqt>
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| fileName(QString())
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| </code>
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| to the <tt>MainWindow</tt> constructor list on line 16. This makes sure that <tt>fileName</tt> is empty right from the beginning.
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|
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| ===Adding the actions===
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|
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| 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 <tt>quit</tt> action in tutorial 3, we will use <tt>KStandardActions</tt>. On lines 37 to 47 we add the actions in the same way as for the <tt>quit</tt> action. For each one, we connect it to the appropriate slot that we declared in the header file.
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|
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| ===Creating a new document===
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|
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| The first function we create is the <tt>newFile()</tt> function.
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| <code cppqt>
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| void MainWindow::newFile()
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| {
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| fileName.clear();
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| textArea->clear();
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| }
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| </code>
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| <tt>fileName.clear()</tt> sets the <tt>fileName</tt> QString to be empty to reflect the fact that this document does not yet have a presence on disc. <tt>textArea->clear()</tt> then clears the central text area using the same function that we connected the <tt>clear</tt> <tt>KAction</tt> to in tutorial 3.
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|
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| ===Saving a file===
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|
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| ====saveFileAs(QString)====
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|
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| 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 {{class|KSaveFile}} which is derived from Qt's {{qt|QFile}}.
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|
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| The function's prototype is
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| <code cppqt>
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| void MainWindow::saveFileAs(const QString &outputFileName)
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| </code>
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|
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| We then create our <tt>KSaveFile</tt> object and open it with
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| <code cppqt>
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| KSaveFile file(outputFileName);
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| file.open();
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| </code>
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|
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| 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 {{qt|QByteArray}} and fill it with the plain text version of whatever is in the text area:
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| <code cppqt>
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| QByteArray outputByteArray;
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| outputByteArray.append(textArea->toPlainText().toUtf8());
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| </code>
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| Now that we have our <tt>QByteArray</tt>, we use it to write to the file with <tt>KSaveFile::write()</tt>. If we were using a normal <tt>QFile</tt>, this would make the changes immediately. However, if a problem occurred partway through writing, the file would become corrupted. For this reason, <tt>KSaveFile</tt> works by first writing to a temporary file and then, when you call <tt>KSaveFile::finalize()</tt> the changes are made to the actual file.
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| <code cppqt>
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| file.write(outputByteArray);
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| file.finalize();
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| file.close();
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| </code>
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| Finally, we set <tt>MainWindows</tt>'s <tt>fileName</tt> member to point to the file name we just saved to.
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| <code cppqt>
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| fileName = outputFileName;
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| </code>
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|
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| ====saveFileAs()====
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|
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| This is the function that the <tt>saveAs</tt> slot is connected to. It simply calls the generic <tt>saveFileAs(QString)</tt> function and passes the file name returned by <tt>{{class|KFileDialog}}::[http://api.kde.org/4.0-api/kdelibs-apidocs/kio/html/classKFileDialog.html#8891356c249c5911e1ab15cc2739a89b getSaveFileName()]</tt>.
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|
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| <code cppqt>
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| void MainWindow::saveFileAs()
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| {
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| saveFileAs(KFileDialog::getSaveFileName());
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| }
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| </code>
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|
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| This is our first actual use of the KIO library. {{class|KFileDialog}} provides a number of static functions for displaying the common file dialog that is used by all KDE applications. Calling <tt>KFileDialog::getSaveFileName()</tt> 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 <tt>saveFileAs(QString)</tt>.
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|
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| ====saveFile()====
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|
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| <code cppqt>
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| void MainWindow::saveFile()
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| {
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| if(!fileName.isEmpty())
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| {
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| saveFileAs(fileName);
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| }
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| else
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| {
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| saveFileAs();
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| }
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| }
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| </code>
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|
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| There's nothing exciting or new in this function, just the logic to decide whether or not to show the save dialog. If <tt>fileName</tt> is not empty, then the file is saved to <tt>fileName</tt>. But if it is, then the dialog is shown to allow the user to select a file name.
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|
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| ===Loading a file===
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|
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| Finally, we get round to being able to load a file from disc. The code for this is all contained in <tt>MainWindow::openFile()</tt>.
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|
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| First we must ask the user for the name of the file they wish to open. We do this using another one of the <tt>KFileDialog</tt> functions, this time <tt>getOpenFileName()</tt>:
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| <code cppqt>
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| QString fileNameFromDialog = KFileDialog::getOpenFileName();
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| </code>
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|
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| 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 {{class|NetAccess}}'s <tt>download()</tt> function
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| <code cppqt>
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| KIO::NetAccess::download(fileNameFromDialog, tmpFile, this)
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| </code>
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| 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 <tt>tmpFile</tt> we will work with from now on.
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|
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| The function returns <tt>true</tt> or <tt>false</tt> depending on whether the transfer was successful. If it failed, we display a message box giving the error:
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| <code cppqt>
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| KMessageBox::error(this, KIO::NetAccess::lastErrorString());
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| </code>
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|
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| Otherwise, we continue with opening the file.
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|
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| We create a QFile by passing the temporary file created by <tt>NetAccess::download()</tt> to its constructor and then open it in read-only mode
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| <code cppqt>
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| QFile file(tmpFile);
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| file.open(QIODevice::ReadOnly);
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| </code>
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|
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| In order to display the contents of the file, we must use a {{class|QTextStream}}. We create one by passing the contents of our file to its constructor and then call QFile's <tt>readAll()</tt> function to get the text from the file. This is then passed to the <tt>setPlainText()</tt> function of our text area.
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|
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| <code cppqt>
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| textArea->setPlainText(QTextStream(&file).readAll());
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| </code>
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|
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| We then store the path of the file we just opened:
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| <code cppqt>
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| fileName = fileNameFromDialog;
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| </code>
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| and finally, we remove the temporary file that was created by <tt>NetAccess::download()</tt>:
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| <code cppqt>
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| KIO::NetAccess::removeTempFile(tmpFile);
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| </code>
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|
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| ==Make, Install And Run==
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|
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| ===CMakeLists.txt===
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| <code ini n>
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| project(tutorial4)
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|
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| find_package(KDE4 REQUIRED)
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| include_directories(${KDE4_INCLUDES})
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|
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| set(tutorial4_SRCS
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| main.cpp
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| mainwindow.cpp
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| )
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|
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| kde4_add_executable(tutorial4 ${tutorial4_SRCS})
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|
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| target_link_libraries(tutorial4 ${KDE4_KDEUI_LIBS}
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| ${KDE4_KIO_LIBS})
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|
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| install(TARGETS tutorial4 DESTINATION ${BIN_INSTALL_DIR})
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| install(FILES tutorial4ui.rc
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| DESTINATION ${DATA_INSTALL_DIR}/tutorial4)
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| </code>
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| Since we are now using the KIO library, we must tell CMake to link against it. We do this by passing <tt>${KDE4_KIO_LIBS}</tt> to the <tt>target_link_libraries()</tt> function.
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|
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| With this file, the tutorial can be built and run in the same way as tutorial 3. For more information, see tutorial 3.
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|
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| mkdir build && cd build
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| cmake .. -DCMAKE_INSTALL_PREFIX=$HOME
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| make install
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| $HOME/bin/tutorial4
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|
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| ==Moving On==
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| Now you can move on to the [[Development/Tutorials/KCmdLineArgs|KCmdLineArgs]] tutorial.
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|
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| [[Category:C++]]
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