QT tutorial: creating the first QT program

One 、 Leading knowledge
1、 The base class represents the parent class 、 Derived classes represent subclasses
2、 Base class QWidget yes QDialog and QMainWindow Parent class of
3、 If you create one, you need to have a menu bar 、 The toolbar 、 Status bar, etc. , You can choose QMainWindow As the base class
4、QDialog As a base class , It's just a simple dialog , There is only one close button in the upper right corner x

Two 、 After the project is successfully created, the code is as follows
1、main.cpp in
#include “mywidget . h” // The class name is the same as the header file name
#include
// Application entry
int main(int argc , char * argv [ ])
{
QApplication a (argv , argv);//QApplication Represents the application class , In every one of them qt There is and only one in the program
MyWidget w;//MyWidget Represents a window class （ After the window class is created, it is not displayed by default , So we'll show it later ）,w Represents the object that created a window class
w . show（）;// Show window ,w It refers to the whole window , When we do other operations on this window , It is equivalent to operating it
return a . exec（）; // Cycle through the window , When a trigger signal or event is received , It will jump out , For example, when closing a window , It will jump out of this cycle
}
2、mywidget.h in
#ifndef MYWIDGET_H
#define MYWIDGET_H
#include

class MyWidget（ Subclass ） : public QWidget （ Parent class ）
{
Q_OBJECT // If signal and slot mechanisms are used , You must add this macro
public :
MyWidget (QWidget *parent = 0) ;// Constructors
~MyWidget（）; // Destructor
};
#endif
3、mywidget.cpp in
#include “mywidget.h”
MyWidget：：MyWidget（QWidget *parent）
: QWidget（parent）
{
}

MyWidget：：~MyWidget（）
{

}
4、xxxxx.pro In Engineering
QT += core gui //qt Modules used in the program
greaterThan（QT_MAJOR_VERSON,4）： QT += widgets // For compatibility with previous versions

TARGET = xxxxx // Generated application name
TEMPLATE = app // Specify the generated makefile The type of lib

SOURCE +=main.cpp
mywidget.cpp // Source file

HEADERS +=mywidget.h // The header file

5、 If a new window needs to be attached to another window , You need to specify a parent class for this window （ It means that the new window is not independent , Instead, it is built in the parent window ）

6、QT After creating pointer in , The condition that memory can be recycled automatically
1） from QObject Derived classes ：1. direct 2. indirect
2） Specify the parent class , When father deconstructs , First analyze its child paper