一、圖形界面應用程序的消息處理模型
二、Qt的事件處理
1、Qt平台將系統產生的消息轉換為Qt事件（每一個系統消息對象Qt平台的一個事件）
（1）、Qt事件是一個QEvent的對象
（2）、Qt事件用於描述程序內部或者外部發生的動作
（3）、任意的QObject對象都具備事件處理的能力
2、GUI應用程序的事件處理方式
（1）、Qt事件產生后立即被分發到QWidget對象
（2）、QWidget中的event（QEvent*）進行事件處理
（3）、event()根據事件類型調用不同的事件處理函數
（4）、在事件處理函數中發送Qt中預定義的信號
（5）、調用信號關聯的槽函數
3、情景分析：按鈕點擊
（1）、接收到鼠標事件（代表一個系統消息）
（2）、調用event(QEvent*)成員函數
（3）、調用MouseReleaseEvent(QMouseEvent*)成員函數
（4）、調用clicked()成員函數
（5）、觸發信號SIGNAL(clicked())
4、事件（QEvent）和信號（SIGNAL）不同
（1）、事件由具體對象進行處理
（2）、信號由具體對象主動產生
（3）、改寫事件處理函數可能導致程序行為發生改變
（4）、信號是否存在對應的槽函數不會改變程序的行為
（5）、一般而言，信號在具體的事件處理函數中產生
三、文本編輯器的關閉操作
void MainWindow::closeEvent(QCloseEvent *e)//沒有對應的信號來處理，只能重寫事件處理函數 { preEditorChanged(); if(!m_isTextChanged) { QMainWindow::closeEvent(e);//調用父類的關閉事件處理函數 } else { e->ignore();//點取消的話就忽略這個對話框 } }
完整代碼：
#ifndef MAINWINDOW_H #define MAINWINDOW_H #include <QMenuBar> #include <QMenu> #include <QAction> #include <QString> #include <QtGui/QMainWindow> #include <QToolBar> #include <QIcon> #include <QSize> #include <QStatusBar> #include <QLabel> #include <QPlainTextEdit> #include <QFileDialog> class MainWindow : public QMainWindow { Q_OBJECT private: QPlainTextEdit mainEdit; QLabel statusLabel; QString m_filePath;//記得在構造函數里初始化 bool m_isTextChanged;//構造函數里初始化為false MainWindow(QWidget *parent = 0); MainWindow(const MainWindow& obj); MainWindow* operator = (const MainWindow& obj); bool construct(); bool initMenuBar();//菜單欄 bool initToolBar();//工具欄 bool initStatusBar();//狀態欄 bool initinitMainEditor();//編輯窗口 bool initFileMenu(QMenuBar* mb);//文件菜單 bool initEditMenu(QMenuBar* mb);//編輯菜單 bool initFormatMenu(QMenuBar* mb);//格式菜單 bool initViewMenu(QMenuBar* mb);//視圖菜單 bool initHelpMenu(QMenuBar* mb);//幫助菜單 bool initFileToolItem(QToolBar* tb);//工具選項 bool initEditToolItem(QToolBar* tb); bool initFormatToolItem(QToolBar* tb); bool initViewToolItem(QToolBar* tb); bool makeAction(QAction*& action,QMenu* menu, QString text, int key);//菜單項 bool makeAction(QAction*& action,QToolBar* tb, QString tip, QString icon); QString showFileDialog(QFileDialog::AcceptMode mode, QString title);//文件對話框 void showErrorMessage(QString message);//錯誤消息對話框 int showQuesstionMessage(QString message);//問題消息對話框 QString saveCurrentData(QString path = ""); void preEditorChanged(); private slots: void onFileNew(); void onFileOpen(); void onFlieSave(); void onFileSaveAs(); void onTextChanged(); protected: void closeEvent(QCloseEvent *e);//重寫關閉窗口的事件處理函數 public: static MainWindow* NewInstance(); ~MainWindow(); }; #endif // MAINWINDOW_H
#include "MainWindow.h" #include <QDebug> MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), statusLabel(this) { m_filePath = ""; m_isTextChanged = false; setWindowTitle("NotePad-[New]"); } bool MainWindow::construct() { bool ret = true; ret = ret && initMenuBar(); ret = ret && initToolBar(); ret = ret && initStatusBar(); ret = ret && initinitMainEditor(); return ret; } MainWindow* MainWindow::NewInstance() { MainWindow* ret = new MainWindow(); if((ret==NULL) || (!ret->construct())) { delete ret; ret = NULL; } return ret; } bool MainWindow::initMenuBar()//菜單欄 { bool ret = true; QMenuBar* mb = menuBar();//一定要注意是menuBar()，這是普通成員函數，不是構造函數 ret = ret && initFileMenu(mb);//傳一個參數是為了在initFileMenu()函數將menu加入菜單欄 ret = ret && initEditMenu(mb); ret = ret && initFormatMenu(mb); ret = ret && initViewMenu(mb); ret = ret && initHelpMenu(mb); return ret; } bool MainWindow::initToolBar()//工具欄 { bool ret = true; QToolBar* tb = addToolBar("Tool Bar"); //tb->setMovable(false); //tb->setFloatable(false); tb->setIconSize(QSize(16,16)); ret = ret && initFileToolItem(tb); tb->addSeparator(); ret = ret && initEditToolItem(tb); tb->addSeparator(); ret = ret && initFormatToolItem(tb); tb->addSeparator(); ret = ret && initViewToolItem(tb); return ret; } bool MainWindow::initStatusBar()//狀態欄 { bool ret = true; QStatusBar* sb = statusBar(); QLabel* label = new QLabel("Made By LGC"); if(label != NULL) { statusLabel.setMinimumWidth(200); statusLabel.setAlignment(Qt::AlignHCenter); statusLabel.setText("Ln:1 Col:1"); label->setMinimumWidth(200); label->setAlignment(Qt::AlignHCenter); sb->addPermanentWidget(new QLabel());//單純加入分隔符 sb->addPermanentWidget(&statusLabel); sb->addPermanentWidget(label); } else { ret = false; } return ret; } bool MainWindow::initinitMainEditor()//編輯窗口 { bool ret = true; mainEdit.setParent(this); setCentralWidget(&mainEdit); connect(&mainEdit, SIGNAL(textChanged()), this, SLOT(onTextChanged())); return ret; } /************************************************文件菜單********************************************************/ bool MainWindow::initFileMenu(QMenuBar* mb) { bool ret = true; QMenu* menu = new QMenu("File(&F)");//創建文件菜單，（&F）是為了可以Alt+F打開 ret = (menu != NULL); if(ret) { QAction* action = NULL; //New ret = ret && makeAction(action, menu, "New(&N)",Qt::CTRL + Qt::Key_N); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileNew())); menu->addAction(action); } menu->addSeparator(); //Open ret = ret && makeAction(action, menu,"Open(&O)...",Qt::CTRL + Qt::Key_O); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileOpen())); menu->addAction(action); } menu->addSeparator(); //Save ret = ret && makeAction(action, menu,"Save(&S)",Qt::CTRL + Qt::Key_S); if(ret) { connect(action, SIGNAL(triggered()), this ,SLOT(onFlieSave())); menu->addAction(action); } menu->addSeparator(); //Save As ret = ret && makeAction(action, menu, "Save As(&A)...",0); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileSaveAs())); menu->addAction(action); } menu->addSeparator(); //print ret = ret && makeAction(action, menu, "Print(&P)...",Qt::CTRL + Qt::Key_P); if(ret) { menu->addAction(action); } menu->addSeparator(); //Exit ret = ret && makeAction(action, menu,"Exit(&X)",0); if(ret) { menu->addAction(action);//將菜單項加入到菜單 } } if(ret) { mb->addMenu(menu);//將菜單加入到菜單欄 } else { delete mb; } return ret; } /************************************************編輯菜單********************************************************/ bool MainWindow::initEditMenu(QMenuBar* mb) { bool ret = true; QMenu* menu = new QMenu("Edit(&E)"); ret = (menu != NULL); if(ret) { QAction* action = NULL; //Undo ret = ret && makeAction(action, menu,"Undo(&U)",Qt::CTRL + Qt::Key_Z); if(ret) { menu->addAction(action); } menu->addSeparator(); //Redo ret = ret && makeAction(action, menu,"Redo(&R)...",Qt::CTRL + Qt::Key_Y); if(ret) { menu->addAction(action); } menu->addSeparator(); //Cut ret = ret && makeAction(action, menu,"Cut(&T)",Qt::CTRL + Qt::Key_X); if(ret) { menu->addAction(action); } menu->addSeparator(); //Copy ret = ret && makeAction(action, menu,"Copy(&C)...",Qt::CTRL + Qt::Key_C); if(ret) { menu->addAction(action); } menu->addSeparator(); //Pase ret = ret && makeAction(action, menu,"Pase(&P)...",Qt::CTRL + Qt::Key_V); if(ret) { menu->addAction(action); } menu->addSeparator(); //Delete ret = ret && makeAction(action, menu, "Delete(&L)",Qt::Key_Delete); if(ret) { menu->addAction(action); } menu->addSeparator(); //Find ret = ret && makeAction(action, menu,"Find(&F)...",Qt::CTRL + Qt::Key_F); if(ret) { menu->addAction(action); } menu->addSeparator(); //Replace ret = ret && makeAction(action, menu,"Replace(&R)...",Qt::CTRL + Qt::Key_H); if(ret) { menu->addAction(action); } menu->addSeparator(); //Goto ret = ret && makeAction(action, menu,"Goto(&G)",Qt::CTRL + Qt::Key_G); if(ret) { menu->addAction(action); } menu->addSeparator(); //Select All ret = ret && makeAction(action, menu, "Select All(&A)",Qt::CTRL + Qt::Key_A); if(ret) { menu->addAction(action); } } if(ret) { mb->addMenu(menu); } else { delete mb; } return ret; } /************************************************格式菜單********************************************************/ bool MainWindow::initFormatMenu(QMenuBar* mb) { bool ret = true; QMenu* menu = new QMenu("Format(&O)"); ret = (menu != NULL); if(ret) { QAction* action = NULL; //Auto Wrap ret = ret && makeAction(action, menu,"Auto Wrap(&W)",0); if(ret) { menu->addAction(action); } menu->addSeparator(); //Font ret = ret && makeAction(action, menu,"Font(&F)...",0); if(ret) { menu->addAction(action); } } if(ret) { mb->addMenu(menu); } else { delete mb; } return ret; } /************************************************視圖菜單********************************************************/ bool MainWindow::initViewMenu(QMenuBar* mb) { bool ret = true; QMenu* menu = new QMenu("View(&V)"); ret = (menu != NULL); if(ret) { QAction* action = NULL; //Tool Bar ret = ret && makeAction(action, menu,"Tool Bar(&T)",0); if(ret) { menu->addAction(action); } menu->addSeparator(); //Status Bar ret = ret && makeAction(action, menu,"Status Bar(&S)",0); if(ret) { menu->addAction(action); } } if(ret) { mb->addMenu(menu); } else { delete mb; } return ret; } /************************************************幫助菜單********************************************************/ bool MainWindow::initHelpMenu(QMenuBar* mb) { bool ret = true; QMenu* menu = new QMenu("Help(&H)"); ret = (menu != NULL); if(ret) { QAction* action = NULL; //User Manual ret = ret && makeAction(action, menu,"User Manual",0); if(ret) { menu->addAction(action); } menu->addSeparator(); //About NotePad ret = ret && makeAction(action, menu,"About NotePad...",0); if(ret) { menu->addAction(action); } } if(ret) { mb->addMenu(menu); } else { delete mb; } return ret; } /*****************************************工具************************************************************/ bool MainWindow::initFileToolItem(QToolBar* tb) { bool ret = true; QAction* action = NULL; ret = ret && makeAction(action, tb, "New", ":/Res/pic/new.png"); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileNew())); tb->addAction(action); } ret = ret && makeAction(action, tb,"Open", ":/Res/pic/open.png"); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileOpen())); tb->addAction(action); } ret = ret && makeAction(action, tb,"Save", ":/Res/pic/save.png"); if(ret) { connect(action, SIGNAL(triggered()), this ,SLOT(onFlieSave())); tb->addAction(action); } ret = ret && makeAction(action, tb,"Save As", ":/Res/pic/saveas.png"); if(ret) { connect(action, SIGNAL(triggered()), this, SLOT(onFileSaveAs())); tb->addAction(action); } ret = ret && makeAction(action, tb,"Print", ":/Res/pic/print.png"); if(ret) { tb->addAction(action); } return ret; } bool MainWindow::initEditToolItem(QToolBar* tb) { bool ret = true; QAction* action = NULL; ret = ret && makeAction(action, tb,"Undo", ":/Res/pic/undo.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Redo", ":/Res/pic/redo.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb, "Cut", ":/Res/pic/cut.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Copy", ":/Res/pic/copy.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Paste", ":/Res/pic/paste.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Find", ":/Res/pic/find.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Replace", ":/Res/pic/replace.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Goto", ":/Res/pic/goto.png"); if(ret) { tb->addAction(action); } return ret; } bool MainWindow::initFormatToolItem(QToolBar* tb) { bool ret = true; QAction* action = NULL; ret = ret && makeAction(action, tb, "Auto Wrap", ":/Res/pic/wrap.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Font", ":/Res/pic/font.png"); if(ret) { tb->addAction(action); } return ret; } bool MainWindow::initViewToolItem(QToolBar* tb) { bool ret = true; QAction* action = NULL; ret = ret && makeAction(action, tb,"Tool Bar", ":/Res/pic/tool.png"); if(ret) { tb->addAction(action); } ret = ret && makeAction(action, tb,"Status Bar", ":/Res/pic/status.png"); if(ret) { tb->addAction(action); } return ret; } bool MainWindow::makeAction(QAction*& action,QMenu* menu, QString text, int key)//菜單項 { bool ret = true; action = new QAction(text, menu); if(action != NULL) { action->setShortcut(QKeySequence(key));//創建快捷鍵 } else { ret = false; } return ret; } bool MainWindow::makeAction(QAction*& action,QToolBar* tb, QString tip, QString icon) { bool ret = true; action = new QAction("", tb); if(action != NULL) { action->setToolTip(tip); action->setIcon(QIcon(icon)); } else { ret = false; } return ret; } MainWindow::~MainWindow() { }
#include <QFileDialog> #include <QStringList> #include <QFile> #include <QDebug> #include <QMessageBox> #include "MainWindow.h" #include <QMap> QString MainWindow::showFileDialog(QFileDialog::AcceptMode mode, QString title) { QString ret = ""; QFileDialog fd; QStringList filters; QMap<QString, QString> map; const char* fileArray[][2]= { {"Text(*.txt)", ".txt"}, {"All Files(*.*)", "*" }, {NULL, NULL} }; for(int i=0; fileArray[i][0] != NULL; i++) { filters.append(fileArray[i][0]); map.insert(fileArray[i][0], fileArray[i][1]); } fd.setWindowTitle(title); fd.setAcceptMode(mode); fd.setNameFilters(filters); if(mode==QFileDialog::AcceptOpen) { fd.setFileMode(QFileDialog::ExistingFile); } if(fd.exec()==QFileDialog::Accepted) { ret = fd.selectedFiles()[0]; QString posix = map[fd.selectedNameFilter()];//把下拉中選中的后綴對應鍵值取出 if(posix != "*" && !ret.endsWith(posix)) { ret += posix; } } return ret; } void MainWindow::showErrorMessage(QString message) { QMessageBox mb(this); mb.setWindowTitle("Quession"); mb.setText(message); mb.setIcon(QMessageBox::Critical); mb.setStandardButtons(QMessageBox::Ok); mb.exec(); } int MainWindow::showQuesstionMessage(QString message) { QMessageBox mb(this); mb.setWindowTitle("Error"); mb.setText(message); mb.setIcon(QMessageBox::Question); mb.setStandardButtons(QMessageBox::Yes | QMessageBox::No | QMessageBox::Cancel); return mb.exec(); } QString MainWindow::saveCurrentData(QString path) { QString ret = path; if(ret == "") { ret = showFileDialog(QFileDialog::AcceptSave, "Save"); } if(ret != "") { QFile file(ret); if(file.open(QIODevice::WriteOnly | QIODevice::Text)) { QTextStream out(&file); out << QString(mainEdit.toPlainText()); file.close(); setWindowTitle("NotePad - [" + ret + "]"); m_isTextChanged = false;//保存后修改狀態值 } else { showErrorMessage(QString("Open file Error!\n\n") + "\"" + m_filePath + "\""); ret = ""; } } return ret; } void MainWindow::preEditorChanged() { if(m_isTextChanged) { int r = showQuesstionMessage("Do you want to Save?"); switch (r) { case QMessageBox::Yes: saveCurrentData(m_filePath); break; case QMessageBox::No: m_isTextChanged = false; break; case QMessageBox::Cancel: break; } } } void MainWindow::onFileNew() { preEditorChanged(); if(!m_isTextChanged) { mainEdit.clear(); m_filePath = ""; m_isTextChanged = false; setWindowTitle("NotePad-[New]"); } } void MainWindow::onFileOpen() { preEditorChanged(); if(!m_isTextChanged) { QString path = showFileDialog(QFileDialog::AcceptOpen, "open"); if(path != "") { QFile file(path); if(file.open(QIODevice::ReadOnly | QIODevice::Text)) { mainEdit.setPlainText(QString(file.readAll())); file.close(); m_filePath = path;//報存當前文件路徑 setWindowTitle("NotePad - [" + m_filePath + "]"); } else { showErrorMessage(QString("Open file Error!\n\n") + "\"" + m_filePath + "\""); } } } } void MainWindow::onFlieSave() { QString path = saveCurrentData(m_filePath); if(path != "") { m_filePath = path; } } void MainWindow::onFileSaveAs() { QString path = saveCurrentData();//使用默認參數 if(path != "") { m_filePath = path; } } void MainWindow::onTextChanged() { if(!m_isTextChanged) { setWindowTitle("*" + windowTitle()); } m_isTextChanged = true; } void MainWindow::closeEvent(QCloseEvent *e)//沒有對應的信號來處理，只能重寫事件處理函數 { preEditorChanged(); if(!m_isTextChanged) { QMainWindow::closeEvent(e);//調用父類的關閉事件處理函數 } else { e->ignore();//點取消的話就忽略這個對話框 } }
#include <QtGui/QApplication> #include "MainWindow.h" #include <QTextCodec> int main(int argc, char *argv[]) { QTextCodec::setCodecForLocale(QTextCodec::codecForName("GBK")); //路徑名支持中文 QTextCodec::setCodecForTr(QTextCodec::codecForName("GBK")); //QString支持中文 QTextCodec::setCodecForCStrings(QTextCodec::codecForName("GBK")); //string支持中文 QApplication a(argc, argv); MainWindow* w = MainWindow::NewInstance(); int ret = -1; if(w != NULL) { w->show(); ret = a.exec(); } delete w; return ret; }
四、小結
（1）、事件（QEvent）和信號（SIGNAL）不同
（2）、事件由QObject對象進行處理
（3）、信號由QObject對象觸發
（4）、重寫事件處理函數可能改變程序行為
（5）、信號的觸發不會對程序行為造成影響
（6）、事件處理是在實際工程開發中的應用非常普遍