2. QT-window component (QWidget), QT coordinate system, preliminary exploration of message processing (signal and slot)

The main contents of this chapter are as follows:

1) Window component (QWidget)
2) QT coordinate system
3) Initial exploration of message processing (signals and slots)

Window component (QWidget)

introduce

Qt builds graphical user interfaces as component objects
A top-level component without a parent component in Qt is called a window
The types of components are divided into:
Container class (parent component) : interface component used to contain functionality
Functional class (subcomponent) : used to implement specific interactive functions

As shown below:

For example, the above QgroupBox is a functional class (sub-component) that belongs to the top-level component , and is also the parent component (container) of three functional class components.

component inheritance

All window components in Qt inherit from the QWidget class , which in turn inherits from the QObject class and the QPaintDevice class.

As shown in the following figure (only 3 window component classes are exemplified):

Introduction to QWidget components

QWidget can draw itself (because it inherits the QPaintDevice class) , and can also handle user input, such as clicking a button
QWidget is the parent class of the Qt window component class
Every widget in Qt can be used as a QWidget (because subclasses can initialize the parent class)
QWidget class objects are often used as parent components or top-level components

A Preliminary Study of QWidget

1) Create a new project, select the Qt Gui application, and set the class information:

2) Generate QWidget template

Run the template:

You can see that a window is generated, and then let's take a look at how the template code is generated.

3) The template code looks like this

#include <QtGui/QApplication>

#include "widget.h"

int main(int argc, char *argv[])

{

    QApplication a(argc, argv);

    QWidget w;                  // Create QWidget class object 

    w.show();                   // Display QWidget class object

   

    return a.exec();

}

According to the content mentioned before, it can be found that since the above QWidget w object has no parent component, QWidget w becomes a top-level component without a parent component, thus generating a window .

Qt coordinate system

introduce

Qt uses a unified coordinate system to position and size widgets
The QWidget class provides component classes with the coordinate system member functions required by widgets

In Qt, coordinate types are divided into

Positioning of top-level widgets
Positioning of widgets within a window
Widget size settings

Coordinate location diagram, as shown below

Common coordinate system member functions provided by the QWidget class are:

resize() : Set the width and height inside the window (width() and height() values)
move() : set the x,y coordinates of the entire window (x() and y() values)
setGeometry() : Set the x, y, w, h inside the window (excluding the title and window border)
size() : Get the size of the widget
pos() : Get the position of the widget
x() : Get the x coordinate of the entire window
y() : Get the y coordinate of the entire window
width() : Get the width inside the window (excluding the width of the outer border)
height() : 获取窗口内部的高度(不包括窗口标题栏的高度)
const QRect& geometry () : 获取窗口内部的x,y,w,h(不包括标题和窗口边框)
const QRect& framgeometry () : 获取整个窗口的x,y,w,h

可以参考下图所示

注意: 在代码里,执行show()后, 再获取 x,y,w,h坐标才有效

接下来我们通过3组不同的获取坐标函数,来打印(x,y,w,h)坐标信息

代码如下所示:

#include <QtGui>
#include "widget.h"
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    QPushButton b("button",&w);   //生成 QPushButton对象， 其父组件为 QWidget

    /*设置窗口大小位置*/
    w.resize(200,300);
    w.move(300,300);

    /*设置按钮大小位置*/
    b.resize(100,50);
    b.move(50,100);
    w.show();

    qDebug()<<"QWidget:";
    qDebug()<<"x()="<<w.x();
    qDebug()<<"y()="<<w.y();
    qDebug()<<"width()="<<w.width();
    qDebug()<<"height()="<<w.height();
    qDebug()<<"QWidget::geometry()";
    qDebug()<<"x="<<w.geometry().x();
    qDebug()<<"y="<<w.geometry().y();
    qDebug()<<"w="<<w.geometry().width();
    qDebug()<<"h="<<w.geometry().height();
    qDebug()<<"QWidget::frameGeometry()";
    qDebug()<<"x="<<w.frameGeometry().x();
    qDebug()<<"y="<<w.frameGeometry().y();
    qDebug()<<"w="<<w.frameGeometry().width();
    qDebug()<<"h="<<w.frameGeometry().height();
    return a.exec();
}

运行打印:

QWidget:
x()= 300
y()= 300
width()= 200
height()= 300

QWidget::geometry()
x= 308
y= 330
w= 200
h= 300

QWidget::frameGeometry()
x= 300
y= 300
w= 216
h= 338

可以看到,获取的窗内坐标(x,y)永远比窗外坐标大,窗外大小(w,h)永远比窗内大小大

初探消息处理(信号与槽)

QT封装了具体操作系统的消息机制,如下图所示:

Qt中定义了与系统信息相关的概念

信号(signal)

由操作系统产生的消息,比如按键消息

槽(slot)

程序中的消息处理函数,用来处理信号,比如处理按键点击信号

连接(Connect)

将系统信息绑定到信息处理函数(信号到槽的连接),通过connect()函数实现,且必须发生在两个Qt类对象之间,如下图所示:

connect()函数原型

bool QObject::connect (
　　　　　　　　const QObject * sender,             　　  //发送对象
　　　　　　　　const char * signal,                     //消息名(信息)
　　　　　　　　const QObject * receiver,                //接收对象
　　　　　　　　const char * method,                     //接收对象的成员函数(槽)
　　　　　　　　Qt::ConnectionType type = Qt::AutoConnection ) ;   //正常情况不需要设置

//当出现sender对象的signal信号,则会自动调用receiver对象的method槽

在信号与槽里,Qt引进了几个新的关键字:

SIGNAL :指定消息名(信号),用于connect()函数里
SLOT : 指定消息处理函数名(槽),用于connect()函数里
Q_OBJECT : 指定该类拥有槽(消息处理),在类声明的内部开始处加上Q_OBJECT即可
slots : 用于在类中声明消息处理函数,比如:

private slots:
         void buttonCliked();

初探信号与槽

通过点击按钮,使程序自动退出,代码如下所示:

#include <QtGui>
#include <QApplication>
#include <QPushButton>

int main(int argc,char * argv[])
{
　　QApplication app(argc,argv);
　　QPushButton *quitButton = new QPushButton("Quit");

　　QObject::connect(quitButton, SIGNAL(clicked()), &app, SLOT(quit()));
　　//*quitButton(发送对象), &app(接收对象)
　　//quit()作用是退出程序, QApplication的成员函数
　　//clicked()作用是鼠标点击, 很多常用组件的成员函数

    quitButton->show();
    return app.exec();
}

其中上面的quit() 和clicked()都是系统预定义好的,接下来我们自定义槽

首先需要注意

类中声明槽(处理信号的成员函数)时,需要slots声明
槽和信号的函数参数必须一致,比如clicked()和quit()都是无参数的
SIGNAL和SLOT指定的函数(信号和槽)只能包含参数类型,不能包含参数名

开始试验,通过不同按钮点击,来打印不同的信息

写QButtonDebug.h:

#ifndef QBUTTONDEBUG_H
#define QBUTTONDEBUG_H

#include <QWidget>
#include <QPushButton>

class QButtonDebug : public QWidget
{
    Q_OBJECT       //指定该类拥有slots(槽)

private:
    QPushButton *mbton1;
    QPushButton *mbton2;

private slots:              //通过slots 声明 槽
    void buttonCliked();

public:
    explicit QButtonDebug(QWidget *parent=0,Qt::WindowFlags f=0);
};

#endif

写QButtonDebug.cpp:

#include "QButtonDebug.h"
#include <QDebug>

QButtonDebug:: QButtonDebug(QWidget *parent,Qt::WindowFlags f) :
    QWidget(parent,f)   //显示初始化父类
{
    mbton1 = new QPushButton("button1",this);
    mbton2 = new QPushButton("button2",this);
    /*设置按钮坐标*/
    mbton1->resize(100,50);
    mbton1->move(50,50);
    mbton2->resize(100,50);
    mbton2->move(50,100);
    /*设置连接*/
    QObject::connect(mbton1,SIGNAL(clicked()),this,SLOT(buttonCliked()));
    QObject::connect(mbton2,SIGNAL(clicked()),this,SLOT(buttonCliked()));
    QWidget::show();
}

void QButtonDebug:: buttonCliked()  　　　　　　　　　　//消息处理函数
{
    QPushButton* p_buton =(QPushButton*)sender();    //获取发送信号的对象
    qDebug()<< p_buton->text();                      //更据不同的按钮 打印不同信息
}

写main.cpp

#include <QtGui>
#include <QApplication>
#include "QButtonDebug.h"

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

　　QButtonDebug b(NULL,Qt::WindowCloseButtonHint);      
                     // Qt::WindowCloseButtonHint:去掉标题按钮提示

　　return a.exec();
}

运行测试

如下图所示,可以看到通过点击不同的按钮,便能打印不同的信息出来

2. QT-window component (QWidget), QT coordinate system, preliminary exploration of message processing (signal and slot)

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