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效果圖如下：

專案結構：

程式主要功能：

1、新建文字檔案。

2、多文件編輯文字檔案。

3、開啟已有檔案。

4、檔案另存為。

解析：

1、 Editor 類繼承自 QTextEdit，主要用於文字編輯和處理功能。

2、MainWindow繼承自QMainWindow，主要用於建立主介面，介面佈局等功能。

原始碼：

//main.cpp

#include <QApplication>
#include "mainwindow.h"

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

    MainWindow mainWin; //建立一個程式例項
    mainWin.show();

    return app.exec();
}
 

//Editor.h

#ifndef EDITOR_H
#define EDITOR_H

#include <QTextEdit>

class Editor : public QTextEdit
{
    Q_OBJECT

public:
    Editor(QWidget *parent = 0);

    void newFile(); //新建檔案
    bool save();  //檔案儲存
    bool saveAs(); //檔案另存為
    QSize sizeHint() const;  //獲取視窗的推薦大小
    QAction *windowMenuAction() const { return action; }

    static Editor *open(QWidget *parent = 0); //開啟視窗
    static Editor *openFile(const QString &fileName, QWidget *parent = 0);  //開啟檔案

protected:
    void closeEvent(QCloseEvent *event);  //關閉事件，在程式關閉之前執行此函式

private slots:
    void documentWasModified(); //設定視窗顯示狀態，修改和未修改兩種

private:
    bool okToContinue();
    bool saveFile(const QString &fileName); //儲存檔案
    void setCurrentFile(const QString &fileName);  //設定當前檔案
    bool readFile(const QString &fileName); //讀檔案
    bool writeFile(const QString &fileName); //寫檔案
    QString strippedName(const QString &fullFileName);  //從檔案路徑中剝取檔名

    QString curFile;
    bool isUntitled;
    QAction *action;
};

#endif
 

#include <QApplication>
#include <QtGui>
#include <QAction>
#include <QMessageBox>
#include <QFileDialog>
#include "editor.h"

Editor::Editor(QWidget *parent)
    : QTextEdit(parent)
{
    action = new QAction(this);
    action->setCheckable(true);
    connect(action, SIGNAL(triggered()), this, SLOT(show()));
    connect(action, SIGNAL(triggered()), this, SLOT(setFocus()));

    isUntitled = true;  //記錄檔案是否已經存在

    connect(document(), SIGNAL(contentsChanged()), this, SLOT(documentWasModified())); //文件內容發生改變時，觸發槽

    setWindowIcon(QPixmap(":/images/document.png"));  //設定子視窗圖示
    setWindowTitle("[*]");
    setAttribute(Qt::WA_DeleteOnClose); //視窗關閉的時候刪除
}

void Editor::newFile()
{
    static int documentNumber = 1; //記錄開啟子視窗的個數

    curFile = tr("document%1.txt").arg(documentNumber);
    setWindowTitle(curFile + "[*]");
    action->setText(curFile);
    isUntitled = true;
    ++documentNumber;
}

bool Editor::save()
{
    if (isUntitled)
        return saveAs();
    else
        return saveFile(curFile);
}

bool Editor::saveAs()
{
    QString fileName =  QFileDialog::getSaveFileName(this, tr("Save As"), curFile);
    if (fileName.isEmpty())
        return false;

    return saveFile(fileName);
}

QSize Editor::sizeHint() const
{
    return QSize(72 * fontMetrics().width('x'), 25 * fontMetrics().lineSpacing());
}

Editor *Editor::open(QWidget *parent) //彈出“開啟”開啟視窗，獲取路徑和檔名
{
    QString fileName = QFileDialog::getOpenFileName(parent, tr("Open"), ".");
    if (fileName.isEmpty())
        return 0;

    return openFile(fileName, parent);
}

Editor *Editor::openFile(const QString &fileName, QWidget *parent)
{
    Editor *editor = new Editor(parent);
    if (editor->readFile(fileName))
    {
        editor->setCurrentFile(fileName);
        return editor;
    }
    else
    {
        delete editor;
        return 0;
    }
}

void Editor::closeEvent(QCloseEvent *event)  //關閉事件發生時
{
    if (okToContinue())
        event->accept(); //接受關閉事件
    else
        event->ignore(); //忽視關閉事件
}

void Editor::documentWasModified() //設定視窗為被修改狀態
{
    setWindowModified(true);
}

bool Editor::okToContinue() //是否繼續
{
    if (document()->isModified()) //判斷檔案是否被修改
    {
        int r = QMessageBox::warning(this, tr("MDI Editor"),
                                     tr("File %1 has been modified.\n" "Do you want to save your changes?")
                                     .arg(strippedName(curFile)),
                                     QMessageBox::Yes | QMessageBox::No | QMessageBox::Cancel);
        if (r == QMessageBox::Yes)
        {
            return save();
        }
        else if (r == QMessageBox::Cancel)
        {
            return false;
        }
    }
    return true;
}

bool Editor::saveFile(const QString &fileName) //儲存檔案
{
    if (writeFile(fileName))
    {
        setCurrentFile(fileName);
        return true;
    }
    else
    {
        return false;
    }
}

void Editor::setCurrentFile(const QString &fileName)  //設定當前檔案
{
    curFile = fileName;
    isUntitled = false;
    action->setText(strippedName(curFile));
    document()->setModified(false);
    setWindowTitle(strippedName(curFile) + "[*]");
    setWindowModified(false);
}

bool Editor::readFile(const QString &fileName) //讀檔案
{
    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
    {
        QMessageBox::warning(this, tr("MDI Editor"),
                             tr("Cannot read file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }

    QTextStream in(&file);
    QApplication::setOverrideCursor(Qt::WaitCursor);
    setPlainText(in.readAll());
    QApplication::restoreOverrideCursor();
    return true;
}

bool Editor::writeFile(const QString &fileName) //寫檔案
{
    QFile file(fileName);
    if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
    {
        QMessageBox::warning(this, tr("MDI Editor"),
                             tr("Cannot write file %1:\n%2.")
                             .arg(file.fileName())
                             .arg(file.errorString()));
        return false;
    }

    QTextStream out(&file);
    QApplication::setOverrideCursor(Qt::WaitCursor);
    out << toPlainText();
    QApplication::restoreOverrideCursor();
    return true;
}

QString Editor::strippedName(const QString &fullFileName) //從路徑中剝離檔名
{
    return QFileInfo(fullFileName).fileName();
}
 

//mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class QAction;
class QActionGroup;
class QLabel;
class QMdiArea;
class QMenu;
class QToolBar;
class Editor;

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();

public slots:
    void newFile();
    void openFile(const QString &fileName);

protected:
    void closeEvent(QCloseEvent *event);

private slots:
    void open();
    void save();
    void saveAs();
    void cut();
    void copy();
    void paste();
    void about();
    void updateActions();
    void loadFiles();

private:
    void createActions();
    void createMenus();
    void createToolBars();
    void createStatusBar();
    void addEditor(Editor *editor);
    Editor *activeEditor();

    QMdiArea *mdiArea;
    QLabel *readyLabel;
    QWidgetList windows;

    QMenu *fileMenu;
    QMenu *editMenu;
    QMenu *windowMenu;
    QMenu *helpMenu;
    QToolBar *fileToolBar;
    QToolBar *editToolBar;
    QActionGroup *windowActionGroup;
    QAction *newAction;
    QAction *openAction;
    QAction *saveAction;
    QAction *saveAsAction;
    QAction *exitAction;
    QAction *cutAction;
    QAction *copyAction;
    QAction *pasteAction;
    QAction *closeAction;
    QAction *closeAllAction;
    QAction *tileAction;
    QAction *cascadeAction;
    QAction *nextAction;
    QAction *previousAction;
    QAction *separatorAction;
    QAction *aboutAction;
    QAction *aboutQtAction;
};

#endif

//mainwindow.cpp

#include <QToolBar>
#include <QLabel>
#include <QtGui>
#include <QMdiArea>
#include <QApplication>
#include <QMessageBox>
#include <QAction>
#include <QMenuBar>
#include <QStatusBar>
#include <QMdiSubWindow>
#include "editor.h"
#include "mainwindow.h"

MainWindow::MainWindow()
{
    mdiArea = new QMdiArea;
    setCentralWidget(mdiArea);
    connect(mdiArea, SIGNAL(subWindowActivated(QMdiSubWindow*)),this, SLOT(updateActions()));

    createActions();
    createMenus();
    createToolBars();
    createStatusBar();

    setWindowIcon(QPixmap(":/images/icon.png"));
    setWindowTitle(tr("MDI Editor"));
    QTimer::singleShot(0, this, SLOT(loadFiles()));
}

void MainWindow::loadFiles()
{
    QStringList args = QApplication::arguments();
    args.removeFirst();
    if (!args.isEmpty())
    {
        foreach (QString arg, args)
            openFile(arg);
        mdiArea->cascadeSubWindows();
    }
    else
    {
        newFile();
    }
    mdiArea->activateNextSubWindow();
}

void MainWindow::newFile()
{
    Editor *editor = new Editor;
    editor->newFile();
    addEditor(editor);
}

void MainWindow::openFile(const QString &fileName)
{
    Editor *editor = Editor::openFile(fileName, this);
    if (editor)
        addEditor(editor);
}

void MainWindow::closeEvent(QCloseEvent *event)
{
    mdiArea->closeAllSubWindows();
    if (!mdiArea->subWindowList().isEmpty())
    {
        event->ignore();
    }
    else
    {
        event->accept();
    }
}

void MainWindow::open()
{
    Editor *editor = Editor::open(this);
    if (editor)
        addEditor(editor);
}

void MainWindow::save()
{
    if (activeEditor())
        activeEditor()->save();
}

void MainWindow::saveAs()
{
    if (activeEditor())
        activeEditor()->saveAs();
}

void MainWindow::cut()
{
    if (activeEditor())
        activeEditor()->cut();
}

void MainWindow::copy()
{
    if (activeEditor())
        activeEditor()->copy();
}

void MainWindow::paste()
{
    if (activeEditor())
        activeEditor()->paste();
}

void MainWindow::about()
{
    QMessageBox::about(this, tr("About MDI Editor"),
            tr("<h2>Editor 1.1</h2>"
               "<p>Copyright &copy; 2007 Software Inc."
               "<p>MDI Editor is a small application that demonstrates "
               "QMdiArea."));
}

void MainWindow::updateActions()
{
    bool hasEditor = (activeEditor() != 0);
    bool hasSelection = activeEditor() && activeEditor()->textCursor().hasSelection();

    saveAction->setEnabled(hasEditor);
    saveAsAction->setEnabled(hasEditor);
    cutAction->setEnabled(hasSelection);
    copyAction->setEnabled(hasSelection);
    pasteAction->setEnabled(hasEditor);
    closeAction->setEnabled(hasEditor);
    closeAllAction->setEnabled(hasEditor);
    tileAction->setEnabled(hasEditor);
    cascadeAction->setEnabled(hasEditor);
    nextAction->setEnabled(hasEditor);
    previousAction->setEnabled(hasEditor);
    separatorAction->setVisible(hasEditor);

    if (activeEditor())
        activeEditor()->windowMenuAction()->setChecked(true);
}

void MainWindow::createActions()
{
    newAction = new QAction(tr("&New"), this);
    newAction->setIcon(QIcon(":/images/new.png"));
    newAction->setShortcut(QKeySequence::New);
    newAction->setStatusTip(tr("Create a new file"));
    connect(newAction, SIGNAL(triggered()), this, SLOT(newFile()));

    openAction = new QAction(tr("&Open..."), this);
    openAction->setIcon(QIcon(":/images/open.png"));
    openAction->setShortcut(QKeySequence::Open);
    openAction->setStatusTip(tr("Open an existing file"));
    connect(openAction, SIGNAL(triggered()), this, SLOT(open()));

    saveAction = new QAction(tr("&Save"), this);
    saveAction->setIcon(QIcon(":/images/save.png"));
    saveAction->setShortcut(QKeySequence::Save);
    saveAction->setStatusTip(tr("Save the file to disk"));
    connect(saveAction, SIGNAL(triggered()), this, SLOT(save()));

    saveAsAction = new QAction(tr("Save &As..."), this);
    saveAsAction->setStatusTip(tr("Save the file under a new name"));
    connect(saveAsAction, SIGNAL(triggered()), this, SLOT(saveAs()));

    exitAction = new QAction(tr("E&xit"), this);
    exitAction->setShortcut(tr("Ctrl+Q"));
    exitAction->setStatusTip(tr("Exit the application"));
    connect(exitAction, SIGNAL(triggered()), this, SLOT(close()));

    cutAction = new QAction(tr("Cu&t"), this);
    cutAction->setIcon(QIcon(":/images/cut.png"));
    cutAction->setShortcut(QKeySequence::Cut);
    cutAction->setStatusTip(tr("Cut the current selection to the "
                               "clipboard"));
    connect(cutAction, SIGNAL(triggered()), this, SLOT(cut()));

    copyAction = new QAction(tr("&Copy"), this);
    copyAction->setIcon(QIcon(":/images/copy.png"));
    copyAction->setShortcut(QKeySequence::Copy);
    copyAction->setStatusTip(tr("Copy the current selection to the "
                                "clipboard"));
    connect(copyAction, SIGNAL(triggered()), this, SLOT(copy()));

    pasteAction = new QAction(tr("&Paste"), this);
    pasteAction->setIcon(QIcon(":/images/paste.png"));
    pasteAction->setShortcut(QKeySequence::Paste);
    pasteAction->setStatusTip(tr("Paste the clipboard's contents at "
                                 "the cursor position"));
    connect(pasteAction, SIGNAL(triggered()), this, SLOT(paste()));

    closeAction = new QAction(tr("Cl&ose"), this);
    closeAction->setShortcut(QKeySequence::Close);
    closeAction->setStatusTip(tr("Close the active window"));
    connect(closeAction, SIGNAL(triggered()), mdiArea, SLOT(closeActiveSubWindow()));

    closeAllAction = new QAction(tr("Close &All"), this);
    closeAllAction->setStatusTip(tr("Close all the windows"));
    connect(closeAllAction, SIGNAL(triggered()), this, SLOT(close()));

    tileAction = new QAction(tr("&Tile"), this);
    tileAction->setStatusTip(tr("Tile the windows"));
    connect(tileAction, SIGNAL(triggered()), mdiArea, SLOT(tileSubWindows()));

    cascadeAction = new QAction(tr("&Cascade"), this);
    cascadeAction->setStatusTip(tr("Cascade the windows"));
    connect(cascadeAction, SIGNAL(triggered()), mdiArea, SLOT(cascadeSubWindows()));

    nextAction = new QAction(tr("Ne&xt"), this);
    nextAction->setShortcut(QKeySequence::NextChild);
    nextAction->setStatusTip(tr("Move the focus to the next window"));
    connect(nextAction, SIGNAL(triggered()), mdiArea, SLOT(activateNextSubWindow()));

    previousAction = new QAction(tr("Pre&vious"), this);
    previousAction->setShortcut(QKeySequence::PreviousChild);
    previousAction->setStatusTip(tr("Move the focus to the previous " "window"));
    connect(previousAction, SIGNAL(triggered()),mdiArea, SLOT(activatePreviousSubWindow()));

    separatorAction = new QAction(this);
    separatorAction->setSeparator(true);

    aboutAction = new QAction(tr("&About"), this);
    aboutAction->setStatusTip(tr("Show the application's About box"));
    connect(aboutAction, SIGNAL(triggered()), this, SLOT(about()));

    aboutQtAction = new QAction(tr("About &Qt"), this);
    aboutQtAction->setStatusTip(tr("Show the Qt library's About box"));
    connect(aboutQtAction, SIGNAL(triggered()), qApp, SLOT(aboutQt()));

    windowActionGroup = new QActionGroup(this);
}

void MainWindow::createMenus()
{
    fileMenu = menuBar()->addMenu(tr("&File"));
    fileMenu->addAction(newAction);
    fileMenu->addAction(openAction);
    fileMenu->addAction(saveAction);
    fileMenu->addAction(saveAsAction);
    fileMenu->addSeparator();
    fileMenu->addAction(exitAction);

    editMenu = menuBar()->addMenu(tr("&Edit"));
    editMenu->addAction(cutAction);
    editMenu->addAction(copyAction);
    editMenu->addAction(pasteAction);

    windowMenu = menuBar()->addMenu(tr("&Window"));
    windowMenu->addAction(closeAction);
    windowMenu->addAction(closeAllAction);
    windowMenu->addSeparator();
    windowMenu->addAction(tileAction);
    windowMenu->addAction(cascadeAction);
    windowMenu->addSeparator();
    windowMenu->addAction(nextAction);
    windowMenu->addAction(previousAction);
    windowMenu->addAction(separatorAction);

    menuBar()->addSeparator();

    helpMenu = menuBar()->addMenu(tr("&Help"));
    helpMenu->addAction(aboutAction);
    helpMenu->addAction(aboutQtAction);
}

void MainWindow::createToolBars()
{
    fileToolBar = addToolBar(tr("File"));
    fileToolBar->addAction(newAction);
    fileToolBar->addAction(openAction);
    fileToolBar->addAction(saveAction);

    editToolBar = addToolBar(tr("Edit"));
    editToolBar->addAction(cutAction);
    editToolBar->addAction(copyAction);
    editToolBar->addAction(pasteAction);
}

void MainWindow::createStatusBar()
{
    readyLabel = new QLabel(tr(" Ready"));
    statusBar()->addWidget(readyLabel, 1);
}

void MainWindow::addEditor(Editor *editor)
{
    connect(editor, SIGNAL(copyAvailable(bool)),
            cutAction, SLOT(setEnabled(bool)));
    connect(editor, SIGNAL(copyAvailable(bool)),
            copyAction, SLOT(setEnabled(bool)));

    QMdiSubWindow *subWindow = mdiArea->addSubWindow(editor);
    windowMenu->addAction(editor->windowMenuAction());
    windowActionGroup->addAction(editor->windowMenuAction());
    subWindow->show();
}

Editor *MainWindow::activeEditor()
{
    QMdiSubWindow *subWindow = mdiArea->activeSubWindow();
    if (subWindow)
        return qobject_cast<Editor *>(subWindow->widget());
    return 0;
}

原始碼下載地址：