How does Qt control the control of MainWindow in other cpp files

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Method 1
Add a public pointer type static member variable of this class to the MainWindow class, and other files use this pointer to manipulate the controls in MainWindow.

Explanation:
The following shows how to create a listForm interface by pressing a button from mainWindow, and then control the edit box of the mainWindow window through an Insert and a Delete button on the listForm interface.

The mainWindow.h file is as follows:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <listform.h>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

public:
    static MainWindow *mutualUi;//!!!!!!!!!指针类型静态成员变量
    void setLinetext(QString s);
private slots:
    void on_pushButton_clicked();
};

#endif // MAINWINDOW_H

static MainWindow *mutualUi;//!!! Static member variables of pointer type
Why do you need to refer to this statically, detailed explanation of static in c++

The mainWindow.cpp file is as follows:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "qdebug.h"

MainWindow *MainWindow::mutualUi = nullptr;//！！！！初始化，非常重要

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    mutualUi = this;//！！！赋值，非常重要
}

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

void MainWindow::setLinetext(QString s)
{
    ui->lineEdit->setText(s);
}

void MainWindow::on_pushButton_clicked()
{
    listForm *l;
    l = new listForm();
    l->show();

}

MainWindow *MainWindow::mutualUi = nullptr;//! ! ! ! Initialization is very important
mutualUi = this;//! ! ! assignment, very important

listForm.cpp file

#include "listform.h"
#include "ui_listform.h"
#include "mainwindow.h"

listForm::listForm(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::listForm)
{
    ui->setupUi(this);
}

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

void listForm::on_pushButton_clicked()
{
    MainWindow::mutualUi->setLinetext("1111");//通过mainwindow的指针设置文本
}

void listForm::on_pushButton_2_clicked()
{
    MainWindow::mutualUi->setLinetext("");//通过mainwindow的指针设置文本
}

MainWindow::mutualUi->setLinetext("1111");//Set the text
listForm.h file through the pointer of mainwindow:

#ifndef LISTFORM_H
#define LISTFORM_H

#include <QWidget>

namespace Ui {
class listForm;
}

class listForm : public QWidget
{
    Q_OBJECT

public:
    explicit listForm(QWidget *parent = 0);
    ~listForm();

private slots:
    void on_pushButton_clicked();

    void on_pushButton_2_clicked();

private:
    Ui::listForm *ui;
};

#endif // LISTFORM_H

Effect display:
run:

Create a listForm window:

Click Insert:

Click to delete:

How does Qt control the control of MainWindow in other cpp files

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