Qt中的信号与槽机制
qt中槽和普通的C++成员函数几乎是一样的--可以是虚函数，可以被重载，可以是共有的，保护的或者私有的。
槽可以和信号连接在一起，在这种情况下，每当发射这个信号的信号，就会自动调用这个槽
connect语句：connect(sende, SIGNAL(signal), receiver, SLOT(slot)
这里的sender和receiver是指向QObject的指针，signal和slot是不带参数的函数名，实际上SIGNAL和SLOT宏会把他们的参数转换成相应的字符串
注意：
一个信号可以连接多个槽
connect(slider, SIGNAL(valueChanged(int)), spinBox, SLOT(setValue(int)));
connect(slider, SIGNAL(valueChanged(int)), this, SLOT(updateStatusBarIndicator(int)));
多个信号可以链接同一个槽
connect(lcd, SIGNAL(overflow)), this, SLOT(handleMathError()));
connect(calculator, SIGNAL(divisionByZero)), this, SLOT(handleMathError()));
一个信号可以与另外一个信号相连接
connect(lineEdit, SIGNAL(textChanged(const QString&)), this, SIGNAL(updateRecord(const QString&)));
Qt的元对象系统机制
元对象系统机制工作原理：
1. Q_OBJECT宏声明了在每一个QObject子类必须实现一些内省函数:metaObject(), tr(), qt_metacall(),以及其他一些函数
2. Qt的moc工具生成了用于由Q_OBJECT声明的所有函数和信号的实现
3. 向connect()和disconnect()这样的QObject的成员函数使用这些内省函数来完成他们的工作
用C++代码实现简单对话框
头文件：findDialog.h
#ifndef FINDDIALOG_H #define FINDDIALOG_H
#include <QLabel>
#include <QDialog>
class QCheckBox;
//class QLabel;
class QLineEdit;
class QPushButton;
class FindDialog : public QDialog
{
Q_OBJECT
public:
//construct function
FindDialog(QWidget *parent = 0);
signals:
void findNext(const QString &str, Qt::CaseSensitivity cs);
void findPrevious(const QString &str, Qt::CaseSensitivity cs);
private slots:
void findCliked();
void enabledFindButton(const QString &text);
private:
QLabel *label;
QCheckBox *caseCheckBox;
QCheckBox *backwardCheckBox;
QPushButton *findButton;
QPushButton *closeButton;
QLineEdit *lineEdit;
};
实现文件findDialog.cpp
#include <QtGui>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QCheckBox>
#include <QLineEdit>
#include <QPushButton>
#include <QMessageBox>
#include "finddialog.h"
FindDialog::FindDialog(QWidget *parent)
:QDialog(parent)
{
label = new QLabel(tr("Find &what:"));
lineEdit = new QLineEdit;
label->setBuddy(lineEdit);
caseCheckBox = new QCheckBox(tr("Match &case"));
backwardCheckBox = new QCheckBox(tr("Search &backword"));
findButton = new QPushButton(tr("&Find"));
findButton->setDefault(true);
findButton->setEnabled(false);
closeButton = new QPushButton(tr("&Clase"));
//链接信号与槽
connect(lineEdit, SIGNAL(textChanged(const QString)),
this, SLOT(enabledFindButton(const QString&)));
connect(findButton, SIGNAL(clicked()),
this, SLOT(findCliked()));
connect(closeButton, SIGNAL(clicked()),
this, SLOT(close()));
//set layout，水平布局管理器
QHBoxLayout *topLeftLayout = new QHBoxLayout;
topLeftLayout->addWidget(label);
topLeftLayout->addWidget(lineEdit);
//垂直布局管理器
QVBoxLayout *leftLayout = new QVBoxLayout;
leftLayout->addLayout(topLeftLayout);
leftLayout->addWidget(caseCheckBox);
leftLayout->addWidget(backwardCheckBox);
QVBoxLayout *rightLayout = new QVBoxLayout;
rightLayout->addWidget(findButton);
rightLayout->addWidget(closeButton);
//Adds a stretchable space (a QSpacerItem) with zero minimum size
//and stretch factor stretch to the end of this box layout.
rightLayout->addStretch();
QHBoxLayout *mainLayout = new QHBoxLayout;
mainLayout->addLayout(leftLayout);
mainLayout->addLayout(rightLayout);
//set the dialog's main layout
setLayout(mainLayout); //设置主对话框的布局
setWindowTitle("Find"); //设置对话框的标题
setFixedHeight(sizeHint().height());
}
//实现槽
void FindDialog::findCliked()
{
QMessageBox msgBox;
msgBox.setText(tr("find successfully!"));
msgBox.exec();
QString text = lineEdit->text();
Qt::CaseSensitivity cs =
caseCheckBox->isChecked() ? Qt::CaseSensitive
: Qt::CaseInsensitive;
if(backwardCheckBox->isChecked()) {
emit findPrevious(text, cs);
}else {
emit findNext(text, cs);
}
}
void FindDialog::enabledFindButton(const QString &text)
{
findButton->setEnabled(!text.isEmpty());
}
创建主窗口
主窗口是构建应用程序用户界面的框架，其中包括菜单，工具栏以及应用程序所需的对话框。那么该如何实现这些功能呢?
子类化QMainWindow（继承MainWindow）
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow();
protected:
void closeEvent(QCloseEvent *event);
private slots:
void newFile();
void open();
bool save();
bool saveAs();
void find();
void goToCell();
void sort();
void about();
void openRecentFile();
void updateStatusBar();
void spreadsheetModified();
......
};
实现代码
MainWindow::MainWindow()
{
spreadsheet = new Spreadsheet;
setCentralWidget(spreadsheet);
createActions(); //创建各个动作
createMenus(); //创建菜单
createContextMenu(); //创建内容菜单
createToolBars(); //创建工具栏
createStatusBar(); //创建状态栏
readSettings(); //读取配置
findDialog = 0;
setWindowIcon(QIcon(":/images/icon.png"));
setCurrentFile("");
}
void MainWindow::closeEvent(QCloseEvent *event)
{
if (okToContinue()) {
writeSettings();
event->accept();
} else {
event->ignore();
}
}
......
图形用户界面(GUI)应用程序通常会使用图片，在Qt使用图片的方法
1. 把图片保存到文件中，并且在运行时载入他们
2. 把XPM文件包含在源代码中
3. 使用Qt的资源机制 (RESOURCE = app_name.qrc)
app_name.qrc:
<RCC>
<qresource>
<file>images/icon.png</file>
<file>images/new.png</file>
<file>images/open.png</file>
<file>images/save.png</file>
<file>images/cut.png</file>
<file>images/copy.png</file>
<file>images/paste.png</file>
<file>images/find.png</file>
<file>images/gotocell.png</file>
</qresource>
</RCC>
创建菜单和工具栏
Qt通过"动作"的概念简化了有关菜单和工具栏的编程。一个Action可以添加到任意数量的菜单和工具栏上的像。实现步骤：
1. 创建并且设置动作
2. 创建菜单栏并且把动作添加的菜单上
3. 创建工具栏并且把动作添加到工具栏
void MainWindow::createActions()
{
newAction = new QAction(tr("&New"), this); //实现创建新文件的动作
newAction->setIcon(QIcon(":/images/new.png"));
newAction->setShortcut(QKeySequence::New);
newAction->setStatusTip(tr("Create a new spreadsheet file"));
connect(newAction, SIGNAL(triggered()), this, SLOT(newFile()));
openAction = new QAction(tr("&Open..."), this); //实现打开文件的动作
openAction->setIcon(QIcon(":/images/open.png"));
openAction->setShortcut(QKeySequence::Open);
openAction->setStatusTip(tr("Open an existing spreadsheet file"));
connect(openAction, SIGNAL(triggered()), this, SLOT(open()));
.........
创建菜单
void MainWindow::createMenus()
{
fileMenu = menuBar()->addMenu(tr("&File"));
fileMenu->addAction(newAction);
fileMenu->addAction(openAction);
fileMenu->addAction(saveAction);
fileMenu->addAction(saveAsAction);
separatorAction = fileMenu->addSeparator();
for (int i = 0; i < MaxRecentFiles; ++i)
fileMenu->addAction(recentFileActions[i]);
fileMenu->addSeparator();
fileMenu->addAction(exitAction);
editMenu = menuBar()->addMenu(tr("&Edit"));
editMenu->addAction(cutAction);
editMenu->addAction(copyAction);
editMenu->addAction(pasteAction);
editMenu->addAction(deleteAction);
.............
设置上下文菜单和工具栏
void MainWindow::createContextMenu()
{
spreadsheet->addAction(cutAction);
spreadsheet->addAction(copyAction);
spreadsheet->addAction(pasteAction);
spreadsheet->setContextMenuPolicy(Qt::ActionsContextMenu);
}
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);
editToolBar->addSeparator();
editToolBar->addAction(findAction);
editToolBar->addAction(goToCellAction);
}
设置状态栏
void MainWindow::createStatusBar()
{
locationLabel = new QLabel(" W999 ");
locationLabel->setAlignment(Qt::AlignHCenter);
locationLabel->setMinimumSize(locationLabel->sizeHint());
formulaLabel = new QLabel;
formulaLabel->setIndent(3);
statusBar()->addWidget(locationLabel);
statusBar()->addWidget(formulaLabel, 1);
connect(spreadsheet, SIGNAL(currentCellChanged(int, int, int, int)),
this, SLOT(updateStatusBar()));
connect(spreadsheet, SIGNAL(modified()),
this, SLOT(spreadsheetModified()));
updateStatusBar();
}
附上以上实现的简单图形界面程序(Spreadsheet)
