QT learning notes (2): QT objects, window coordinates, signals and slots

Note: QT version used for learning is Qt5 nine

I QT object

You need to know that qt after creating an object, the programmer does not need to destroy it manually. To facilitate memory management, when the parent object is destructed, all objects in the child object list will be destructed. When the child object is destructed, it will be automatically deleted from the child object list of the parent object. At the same time, we need to create the parent object first, and then create the child object

II Window coordinates of QT

Coordinate system:

Taking the upper left corner as the origin (0.0), X increases to the right and Y increases downward

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III Signals and slots in QT

You can connect through the connect function

connect(Sender of signal, specific signal sent, receiver of signal, signal processing (slot))

The advantage of the signal slot is loose coupling. The transmitting end and receiving end of the signal are not associated. The two ends are coupled together through connect

Next, use the signal and slot mechanism to close the window. Connect btn3 to the window through connect. The signal slot is closed

#include "mywidget.h"
#include "qpushbutton.h" / / the header file is required to create the button
#include "mypushbutton.h"
myWidget::myWidget(QWidget *parent)
    : QWidget(parent)
{

    //Create first button
    QPushButton *btn = new QPushButton;
    //btn->show();   //  The show method displays the window control in the top-level method by default
    //Let the btn object depend on the window we currently create ourselves
    btn->setParent(this);
    //Set what the button displays
    btn->setText("First button");
    //display
    btn->show();
    //Button size
    btn->resize(150,150);

    //Create a second button to create a window according to the size of the control
    QPushButton *btn2 = new QPushButton("Second button",this);
    //Set the position of the button
    btn2->move(300,300);


    //Set the third custom button
    QPushButton *btn3 =new myPushButton();
    //Sets the parent object of the button
    btn3->setParent(this);
    //Set button display
    btn3->setText("Third button");
    //Set button position
    btn3->move(400,400);
    //Set window title
    setWindowTitle("miss you!");
    //Reset window size
    resize(800,600);
    //Set fixed window size
    setFixedSize(800,600);
    //Parameter 1 sender of signal parameter 2 transmitted signal (function address) parameter 3 receiver of signal parameter 4 processed slot function
    connect(btn3,&QPushButton::clicked,this,&QPushButton::close);


}

myWidget::~myWidget()
{
    qDebug("Destroyed a window");
}

IV Custom signals and slots

be careful:

1. Signals can be connected

2. One signal can connect multiple slot functions

3. Multiple signals can be connected to the same slot function

4. The parameters of signal and slot must correspond one by one

5. The number of parameters of the signal can be more than the number of parameters of the slot

6. The signal slot can disconnect the disconnect function

(1) Create a Student class

#ifndef STUDENT_H
#define STUDENT_H

#include <QObject>
#include <QString>
class Student : public QObject
{
    Q_OBJECT
public:
    explicit Student(QObject *parent = nullptr);

signals:

public slots:
    //It can be written to public or global
    //The return value is void, which needs to be declared and implemented
    //You can also have parameters and overload can occur
    void Studentslots();            //No parameters
    void Studentslots(QString Nfood);   //With parameters
};

#endif // STUDENT_H

(2) Create a Teacher class

#ifndef TEACHER_H
#define TEACHER_H

#include <QObject>

class Teacher : public QObject
{
    Q_OBJECT
public:
    explicit Teacher(QObject *parent = nullptr);

signals:
    //Custom signal definition location
    //The return value is void. You only need to declare it, not implement it
    //It can have parameters and can be overloaded
    void Teachersignals();          //No parameters
    void Teachersignals(QString Nfood);     //With parameters

public slots:
};

#endif // TEACHER_H

(3)widget. Content in CPP

#include "widget.h"
#include "ui_widget.h"
#include "QPushButton"

//Teacher class
//Student class student class
//After class, the teacher will send a signal, and the students will respond to this signal
Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);

    //Create a teacher object
    this->A = new Teacher(this);
    //Create a student object
    this->a = new Student(this);
    QPushButton *btn = new QPushButton("class is over",this);

    this->resize(800,600);
    void (Teacher::*T)(QString A) = &Teacher::Teachersignals;
    void (Student::*S)(QString B) = &Student::Studentslots;
    connect(this->A,T,this->a,S);
    connect(btn,&QPushButton::clicked,this,&Widget::classisover);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::classisover()
{
    emit A->Teachersignals("Kung Pao Chicken");
}

(4) After running the program, click the button

V Summary of signals and slots

Vi practice

Use two buttons to open and close the interface, use one button to open and close the interface, and create two new classes to inherit the QWidget parent class

The code is as follows:

#include "widget.h"
#include "ui_widget.h"
#include "QPushButton"

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    //Create three keys
    QPushButton *btn1 = new QPushButton("open",this);
    QPushButton *btn2 = new QPushButton("close",this);
    QPushButton *btn3 = new QPushButton("open",this);
    //Set the position of the three keys
    btn1->move(0,0);
    btn2->move(100,0);
    btn3->move(400,400);
    //Set the size and title of the main window
    this->resize(800,600);
    this->setWindowTitle("QT_demo");
    //Define flag variables
    static bool flag = 0;
    //Connecting signal and signal slot
    connect(btn1,&QPushButton::clicked,this,[=](){
        if(!flag)
        {
            this->blankwindow = new myWidget();
            blankwindow->show();
            flag = 1;
        }
    });
    connect(btn2,&QPushButton::clicked,this,[=](){
        if(flag)
        {
            blankwindow->deleteLater();
            flag = 0;
        }

    });

    connect(btn3,&QPushButton::clicked,this,[=](){
        if(flag)
        {
            blankwindow->deleteLater();
            flag = 0;
            btn3->setText("open");
        }
        else
        {
            this->blankwindow = new myWidget();
            blankwindow->show();
            flag = 1;
            btn3->setText("close");
        }
    });
}

Widget::~Widget()
{
    delete ui;
}

   btn3->setText("open");
        }
        else
        {
            this->blankwindow = new myWidget();
            blankwindow->show();
            flag = 1;
            btn3->setText("close");
        }
    });
}

Widget::~Widget()
{
    delete ui;
}