From Gossip@caterpillar

Qt3 Gossip: Qt 線上範例 - application

接下來要介紹的這個程式是Qt的線上範例application，這個範例雖然程式碼很長，但大部份的元件我們都已經介紹過了，只要逐步拆解程式碼，相信也可以瞭解它的內容。

要觀看Qt的線上範例，最重要的就是瞭解它的定義檔的內容，即application.h：
  • application.h
#ifndef APPLICATION_H
#define APPLICATION_H

#include <qmainwindow.h>

class QTextEdit;

class ApplicationWindow: public QMainWindow
{
    Q_OBJECT

public:
    ApplicationWindow();
    ~ApplicationWindow();

protected:
    void closeEvent( QCloseEvent* );

private slots:
    void newDoc();
    void choose();
    void load( const QString &fileName );
    void save();
    void saveAs();
    void print();

    void about();
    void aboutQt();

private:
    QPrinter *printer;
    QTextEdit *e;
    QString filename;
};

#endif 

這個程式繼承QMainWindow類別，這是文字編輯器的標準外觀元件；接下來我們一段一段來看application.cpp中的程式碼：
#include "application.h"

#include <qimage.h>
#include <qpixmap.h>
#include <qtoolbar.h>
#include <qtoolbutton.h>
#include <qpopupmenu.h>
#include <qmenubar.h>
#include <qtextedit.h>
#include <qfile.h>
#include <qfiledialog.h>
#include <qstatusbar.h>
#include <qmessagebox.h>
#include <qprinter.h>
#include <qapplication.h>
#include <qaccel.h>
#include <qtextstream.h>
#include <qpainter.h>
#include <qpaintdevicemetrics.h>
#include <qwhatsthis.h>

#include "filesave.xpm"
#include "fileopen.xpm"
#include "fileprint.xpm"

這些不用解釋了，就是include定義檔而已，接下來這些大部份都是在作版面配置，以及Signals - Slots之間的連接：
ApplicationWindow::ApplicationWindow()
    : QMainWindow( 0, "example application main window", WDestructiveClose )
{
    printer = new QPrinter;
    QPixmap openIcon, saveIcon, printIcon;

    QToolBar * fileTools = new QToolBar( this, "file operations" );
    fileTools->setLabel( "File Operations" );

    openIcon = QPixmap( fileopen );
    QToolButton * fileOpen
   = new QToolButton( openIcon, "Open File", QString::null,
            this, SLOT(choose()), fileTools, "open file" );

    saveIcon = QPixmap( filesave );
    QToolButton * fileSave
   = new QToolButton( saveIcon, "Save File", QString::null,
            this, SLOT(save()), fileTools, "save file" );

    printIcon = QPixmap( fileprint );
    QToolButton * filePrint
   = new QToolButton( printIcon, "Print File", QString::null,
            this, SLOT(print()), fileTools, "print file" );

    (void)QWhatsThis::whatsThisButton( fileTools );

    const char * fileOpenText = "<p><img source=\"fileopen\"> "
            "Click this button to open a <em>new file</em>.<br>"
                 "You can also select the <b>Open</b> command "
                 "from the <b>File</b> menu.</p>";

    QWhatsThis::add( fileOpen, fileOpenText );

    QMimeSourceFactory::defaultFactory()->setPixmap( "fileopen", openIcon );

    const char * fileSaveText = "<p>Click this button to save the file you "
                 "are editing. You will be prompted for a file name.\n"
                 "You can also select the <b>Save</b> command "
                 "from the <b>File</b> menu.</p>";

    QWhatsThis::add( fileSave, fileSaveText );

    const char * filePrintText = "Click this button to print the file you "
                 "are editing.\n"
       "You can also select the Print command "
       "from the File menu.";

    QWhatsThis::add( filePrint, filePrintText );


    QPopupMenu * file = new QPopupMenu( this );
    menuBar()->insertItem( "&File", file );


    file->insertItem( "&New", this, SLOT(newDoc()), CTRL+Key_N );

    int id;
    id = file->insertItem( openIcon, "&Open...",
            this, SLOT(choose()), CTRL+Key_O );
    file->setWhatsThis( id, fileOpenText );

    id = file->insertItem( saveIcon, "&Save",
            this, SLOT(save()), CTRL+Key_S );
    file->setWhatsThis( id, fileSaveText );

    id = file->insertItem( "Save &As...", this, SLOT(saveAs()) );
    file->setWhatsThis( id, fileSaveText );

    file->insertSeparator();

    id = file->insertItem( printIcon, "&Print...",
            this, SLOT(print()), CTRL+Key_P );
    file->setWhatsThis( id, filePrintText );

    file->insertSeparator();

    file->insertItem( "&Close", this, SLOT(close()), CTRL+Key_W );

    file->insertItem( "&Quit", qApp, SLOT( closeAllWindows() ), CTRL+Key_Q );

    menuBar()->insertSeparator();

    QPopupMenu * help = new QPopupMenu( this );
    menuBar()->insertItem( "&Help", help );

    help->insertItem( "&About", this, SLOT(about()), Key_F1 );
    help->insertItem( "About &Qt", this, SLOT(aboutQt()) );
    help->insertSeparator();
    help->insertItem( "What's &This", this, SLOT(whatsThis()), SHIFT+Key_F1 );

    e = new QTextEdit( this, "editor" );
    e->setFocus();
    setCentralWidget( e );
    statusBar()->message( "Ready", 2000 );

    resize( 450, 600 );
}

ApplicationWindow::~ApplicationWindow()
{
    delete printer;
}

其中重要的部份有：
// 在QToolBar中置入WhatsThis按鈕
(void)QWhatsThis::whatsThisButton( fileTools );
// 為fileSave按鈕置入WhatsThis說明
QWhatsThis::add( fileSave, fileSaveText );

接下來就都是Slots的實作了：
void ApplicationWindow::newDoc()
{
    ApplicationWindow *ed = new ApplicationWindow;
    ed->setCaption("Qt Example - Application");
    ed->show();
}

按下選單中的New選項會開啟一個新的視窗，這是SDI（Single Document Interface）應用程式的標準作法。

接下來實作，按下選單中的Open或工具列上的開啟圖示，就會顯示開啟檔案的對話方塊，選擇檔案後若開啟成功，就將檔案載入：
void ApplicationWindow::choose()
{
    QString fn = QFileDialog::getOpenFileName( QString::null, QString::null,
                      this);
    if ( !fn.isEmpty() )
   load( fn );
    else
   statusBar()->message( "Loading aborted", 2000 );
}

void ApplicationWindow::load( const QString &fileName )
{
    QFile f( fileName );
    if ( !f.open( IO_ReadOnly ) )
   return;

    QTextStream ts( &f );
    e->setText( ts.read() );
    e->setModified( FALSE );
    setCaption( fileName );
    statusBar()->message( "Loaded document " + fileName, 2000 );
}


按下Save或是工具列上的儲存按鈕時，檢查是否需另存新檔，例如無檔名（新開啟）、唯讀等等情況，否則就直接儲存檔案；按下Save as或檢查必須另存新檔案，就會執行saveAs()這個Slot方法：
void ApplicationWindow::save()
{
    if ( filename.isEmpty() ) {
   saveAs();
   return;
    }

    QString text = e->text();
    QFile f( filename );
    if ( !f.open( IO_WriteOnly ) ) {
   statusBar()->message( QString("Could not write to %1").arg(filename),
               2000 );
   return;
    }

    QTextStream t( &f );
    t << text;
    f.close();

    e->setModified( FALSE );

    setCaption( filename );

    statusBar()->message( QString( "File %1 saved" ).arg( filename ), 2000 );
}

void ApplicationWindow::saveAs()
{
    QString fn = QFileDialog::getSaveFileName( QString::null, QString::null,
                      this );
    if ( !fn.isEmpty() ) {
   filename = fn;
   save();
    } else {
   statusBar()->message( "Saving aborted", 2000 );
    }
}

printer->setup(this) 顯示列印對話方塊的設定畫面，印表機的列印準備是在印表機物件上進行繪圖，p.begin(printer)對印表機物件初始列印工作，接下來我們對繪圖 物件作一些字型與頁面大小的設定，由於我們是準備印表機列印，所以我們需要印表機的頁面大小資訊，這是QPaintDeviceMetrics metrics( printer )這行的作用，然後我們將編輯區域的文字一行一行畫到繪圖物件上，結束後告訴印表機，這是p.end()這行的作用，此時繪圖物件上的資訊會送至印表機開 始列印。

printer->newPage()是在檢查列印位置超出紙張時，另起一個新頁面來繼續列印：
void ApplicationWindow::print()
{
    // ###### Rewrite to use QSimpleRichText to print here as well
    const int Margin = 10;
    int pageNo = 1;

    if ( printer->setup(this) ) {      // printer dialog
   statusBar()->message( "Printing..." );
   QPainter p;
   if( !p.begin( printer ) )               // paint on printer
       return;

   p.setFont( e->font() );
   int yPos   = 0;         // y-position for each line
   QFontMetrics fm = p.fontMetrics();
   QPaintDeviceMetrics metrics( printer ); // need width/height
                  // of printer surface
   for( int i = 0 ; i < e->lines() ; i++ ) {
       if ( Margin + yPos > metrics.height() - Margin ) {
      QString msg( "Printing (page " );
      msg += QString::number( ++pageNo );
      msg += ")...";
      statusBar()->message( msg );
      printer->newPage();      // no more room on this page
      yPos = 0;         // back to top of page
       }
       p.drawText( Margin, Margin + yPos,
         metrics.width(), fm.lineSpacing(),
         ExpandTabs | DontClip,
         e->text( i ) );
       yPos = yPos + fm.lineSpacing();
   }
   p.end();            // send job to printer
   statusBar()->message( "Printing completed", 2000 );
    } else {
   statusBar()->message( "Printing aborted", 2000 );
    }
}

當按下關閉鈕時，檢查看看編輯區域是否有修改過，如果有的話，詢問使用者是否儲存或另儲新檔：
void ApplicationWindow::closeEvent( QCloseEvent* ce )
{
    if ( !e->isModified() ) {
   ce->accept();
   return;
    }

    switch( QMessageBox::information( this, "Qt Application Example",
                  "Do you want to save the changes"
                  " to the document?",
                  "Yes", "No", "Cancel",
                  0, 1 ) ) {
    case 0:
   save();
   ce->accept();
   break;
    case 1:
   ce->accept();
   break;
    case 2:
    default: // just for sanity
   ce->ignore();
   break;
    }
}

接下來這兩個Slots沒什麼，就是顯示「關於」的訊息方塊而已：
void ApplicationWindow::about()
{
    QMessageBox::about( this, "Qt Application Example",
         "This example demonstrates simple use of "
         "QMainWindow,\nQMenuBar and QToolBar.");
}


void ApplicationWindow::aboutQt()
{
    QMessageBox::aboutQt( this, "Qt Application Example" );
}

最後別忘了主函式main.cpp：
  • main.cpp
#include <qapplication.h>
#include "application.h"

int main( int argc, char ** argv ) {
    QApplication a( argc, argv );
    ApplicationWindow * mw = new ApplicationWindow();
    mw->setCaption( "Qt Example - Application" );
    mw->show();
    a.connect( &a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()) );
    return a.exec();
}

程式終於看完了，下圖是這個程式的執行結果畫面：