1、QAction 的信号

• QAction 被点击之后会产生一个 triggered 信号
  — 通过信号与槽的机制能够捕捉对 QAction 对象的操作
  — 项目中可以将多个信号映射到同一个槽函数

connect(action, SIGNAL(triggered()), this, SLOT(slot_function()));

程序：
MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include 
#include 
#include 
#include class MainWindow : public QMainWindow
{Q_OBJECT
private:QPlainTextEdit plainEdit;QLabel statusLbl;QString m_filePath;MainWindow();MainWindow(const MainWindow& obj);bool construct();bool initMenuBar();bool initToolBar();bool initStatusBar();bool initMainEditor();bool initFileMenu(QMenuBar* mb);bool initEditMenu(QMenuBar* mb);bool initFormatMenu(QMenuBar* mb);bool initViewMenu(QMenuBar* mb);bool initHelpMenu(QMenuBar* mb);bool initFileToolItem(QToolBar* tb);bool initEditToolItem(QToolBar* tb);bool initFormatToolItem(QToolBar* tb);bool initViewToolItem(QToolBar* tb);bool makeAction(QAction*& action, QWidget* parent, QString text, int key);bool makeAction(QAction*& action, QWidget* parent, QString text, QString path);QString showFileDialog(QFileDialog::AcceptMode mode, QString title);void showErrorMessage(QString message);private slots:void onFileOpen();void onFileSave();void onFileSaveAs();
public:static MainWindow* NewInstance();~MainWindow();
};
#endif // MAINWINDOW_H

MainWindowUI.cpp

#include "MainWindow.h"
#include 
#include 
#include 
#include 
#include 
#include MainWindow::MainWindow(): QMainWindow()
{m_filePath = "";resize(1000, 800);setWindowTitle("NotePad");
}bool MainWindow::construct()
{bool ret = true;ret = ret && initMenuBar();ret = ret && initToolBar();ret = ret && initStatusBar();ret = ret && initMainEditor();return ret;
}MainWindow* MainWindow::NewInstance()
{MainWindow* ret = new MainWindow();if(!(ret && ret->construct())){delete ret;ret = nullptr;}return ret;
}bool MainWindow::initMenuBar()
{bool ret = true;QMenuBar* mb = menuBar();ret = ret && initFileMenu(mb);ret = ret && initEditMenu(mb);ret = ret && initFormatMenu(mb);ret = ret && initViewMenu(mb);ret = ret && initHelpMenu(mb);return ret;
}bool MainWindow::initToolBar()
{bool ret = true;QToolBar* tb = addToolBar("ToolBar");tb->setFloatable(false);tb->setMovable(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()
{bool ret = true;QStatusBar* sb = statusBar();QLabel* label = new QLabel("D.T.Software");if(label != nullptr){statusLbl.setMinimumWidth(200);statusLbl.setAlignment(Qt::AlignCenter);statusLbl.setText("Ln: 1   Col: 1");label->setMinimumWidth(200);label->setAlignment(Qt::AlignCenter);sb->addPermanentWidget(new QLabel());sb->addPermanentWidget(&statusLbl);sb->addPermanentWidget(label);}else{ret = false;}return ret;
}bool MainWindow::initMainEditor()
{bool ret = true;plainEdit.setParent(this);setCentralWidget(&plainEdit);return ret;
}bool MainWindow::initFileMenu(QMenuBar* mb)
{QMenu* menu = new QMenu("File(&F)", nullptr);bool ret = (menu != nullptr);if(ret){QAction* action = nullptr;ret = ret && makeAction(action, menu, "New(&N)", Qt::CTRL + Qt::Key_N);if(ret){menu->addAction(action);}menu->addSeparator();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();ret = ret && makeAction(action, menu, "Save(&N)", Qt::CTRL + Qt::Key_S);if(ret){connect(action, SIGNAL(triggered()), this, SLOT(onFileSave()));menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Save As(&A)", Qt::CTRL + Qt::SHIFT + Qt::Key_S);if(ret){connect(action, SIGNAL(triggered()), this, SLOT(onFileSaveAs()));menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Print(&P)", Qt::CTRL + Qt::Key_P);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Exit(&X)", 0);if(ret){menu->addAction(action);}menu->addSeparator();}if(ret){mb->addMenu(menu);}else{ret = false;delete menu;}return ret;
}
bool MainWindow::initEditMenu(QMenuBar* mb)
{QMenu* menu = new QMenu("Edit(&E)", nullptr);bool ret = (menu != nullptr);if(ret){QAction* action = nullptr;ret = ret && makeAction(action, menu, "Undo(&U)", Qt::CTRL + Qt::Key_Z);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Redo(&R)", Qt::CTRL + Qt::Key_Y);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Cut(&T)", Qt::CTRL + Qt::Key_X);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Copy(&C)", Qt::CTRL + Qt::Key_C);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Paste(&P)", Qt::CTRL + Qt::Key_V);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Delete(&L)", Qt::Key_Delete);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Find(&F)", Qt::CTRL + Qt::Key_F);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Replace(&R)", Qt::CTRL + Qt::Key_H);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Goto(&G)", Qt::CTRL + Qt::Key_G);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Select All(&A)", Qt::CTRL + Qt::Key_A);if(ret){menu->addAction(action);}menu->addSeparator();}if(ret){mb->addMenu(menu);}else{ret = false;delete menu;}return ret;
}
bool MainWindow::initFormatMenu(QMenuBar* mb)
{QMenu* menu = new QMenu("Format(&O)", nullptr);bool ret = (menu != nullptr);if(ret){QAction* action = nullptr;ret = ret && makeAction(action, menu, "AutoWrap(&W)", 0);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "Font(&F)", 0);if(ret){menu->addAction(action);}menu->addSeparator();}if(ret){mb->addMenu(menu);}else{ret = false;delete menu;}return ret;
}
bool MainWindow::initViewMenu(QMenuBar* mb)
{QMenu* menu = new QMenu("View(&V)", nullptr);bool ret = (menu != nullptr);if(ret){QAction* action = nullptr;ret = ret && makeAction(action, menu, "ToolBar(&T)", 0);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "StatusBar(&S)", 0);if(ret){menu->addAction(action);}menu->addSeparator();}if(ret){mb->addMenu(menu);}else{ret = false;delete menu;}return ret;
}
bool MainWindow::initHelpMenu(QMenuBar* mb)
{QMenu* menu = new QMenu("Help(&H)", nullptr);bool ret = (menu != nullptr);if(ret){QAction* action = nullptr;ret = ret && makeAction(action, menu, "User Manual", 0);if(ret){menu->addAction(action);}menu->addSeparator();ret = ret && makeAction(action, menu, "About NotePad...", 0);if(ret){menu->addAction(action);}menu->addSeparator();}if(ret){mb->addMenu(menu);}else{ret = false;delete menu;}return ret;
}bool MainWindow::initFileToolItem(QToolBar* tb)
{bool ret = true;QAction* action = nullptr;ret = ret && makeAction(action, tb, "New", ":/res/pic/new.png");if(ret){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(onFileSave()));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 = nullptr;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 = nullptr;ret = ret && makeAction(action, tb, "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 = nullptr;ret = ret && makeAction(action, tb, "Tool", ":/res/pic/tool.png");if(ret){tb->addAction(action);}ret = ret && makeAction(action, tb, "Status", ":/res/pic/status.png");if(ret){tb->addAction(action);}return ret;
}bool MainWindow::makeAction(QAction*& action, QWidget* parent, QString text, int key)
{bool ret = true;action = new QAction(text, parent);if(action != nullptr){action->setShortcut(QKeySequence(key));}else{ret = false;}return ret;
}bool MainWindow::makeAction(QAction*& action,  QWidget* parent, QString text, QString path)
{bool ret = true;action = new QAction("", parent);if(action != nullptr){action->setToolTip(text);action->setIcon(QIcon(path));}else{ret = false;}return ret;
}MainWindow::~MainWindow()
{}

MainWindowSlots.cpp

#include "MainWindow.h"
#include 
#include 
#include 
#include 
#include QString MainWindow::showFileDialog(QFileDialog::AcceptMode mode, QString title)
{QString ret = "";QFileDialog flg(this);flg.setAcceptMode(mode);flg.setWindowTitle(title);if(mode == QFileDialog::AcceptOpen){flg.setFileMode(QFileDialog::ExistingFile);}QStringList filters;filters << "Text files (*.txt)"<< "Any files (*)";flg.setNameFilters(filters);if(flg.exec() == QFileDialog::Accepted){ret = flg.selectedFiles()[0];}return ret;
}void MainWindow::showErrorMessage(QString message)
{QMessageBox msg(this);msg.setWindowTitle("Error");msg.setIcon(QMessageBox::Critical);msg.setText(message);msg.setStandardButtons(QMessageBox::Ok);msg.exec();
}void MainWindow::onFileOpen()
{QString path = showFileDialog(QFileDialog::AcceptOpen, "Open");if(path != ""){QFile file(path);if(file.open(QIODevice::ReadOnly | QIODevice::Text)){plainEdit.setPlainText(QString(file.readAll()));file.close();m_filePath = path;setWindowTitle("NotePad - [ " + m_filePath + " ]");}else{showErrorMessage(QString("open file error") + "\"" + path + "\"");}}}void MainWindow::onFileSave()
{if(m_filePath == ""){m_filePath = showFileDialog(QFileDialog::AcceptSave, "Save");}if(m_filePath != ""){QFile file(m_filePath);if(file.open(QIODevice::WriteOnly | QIODevice::Text)){QTextStream out(&file);out << plainEdit.toPlainText();file.close();setWindowTitle("NotePad - [ " + m_filePath + " ]");}else{showErrorMessage(QString("Save file error \n\n") + "\"" + m_filePath + "\"");m_filePath = "";}}
}void MainWindow::onFileSaveAs()
{QString path = showFileDialog(QFileDialog::AcceptSave, "Save as");if(path != ""){QFile file(path);if(file.open(QIODevice::WriteOnly | QIODevice::Text)){QTextStream out(&file);out << plainEdit.toPlainText();file.close();m_filePath = path;setWindowTitle("NotePad - [ " + m_filePath + " ]");}else{showErrorMessage(QString("Save as file error \n\n") + "\"" + m_filePath + "\"");}}
}

main.cpp

#include "MainWindow.h"#include int main(int argc, char *argv[])
{QApplication a(argc, argv);int ret = -1;MainWindow* w = MainWindow::NewInstance();if(w != nullptr){w->show();ret = a.exec();delete w;}return ret;
}

思考：如何判断是否存在为保存的数据？
在文件打开的步骤那里，我们只实现了内部不存在保存的数据，所以我们的程序只有直接打开文件的功能。但是实际上如果内部存在数据，我们要先保存数据，然后再去打开文本。

小结

• Qt 项目中尽量将界面代码和功能代码分离开
• Qt 项目开发时尽量复用平台提供的相关组件
• Qt 项目中的多数情况都是编写相应的槽函数
  — 槽函数用于相应用户操作
  — 槽函数是具体功能的触发点