Day20qt multiple forms switching idea 2021-10-31

Qt Realize the switching of multiple forms

demand ：

The three forms switch back and forth

Be careful ：

1. It should be clear when to allocate memory space for objects , And specify whether to allocate space in the heap or stack area , Avoid flashing the window 、 Constantly create forms, etc , See also Allocate storage space for objects
2. If 1 No. form switches to 2 No. form , Attention should be paid to ,2 The instantiation of Form No. is in 1 In form No , Because in 1 Internal work 2 Display operation of , Be sure to instantiate the object first .
3. If 2 No. form switches back to 1 No. form , Attention should be paid to , because 2 No. form object in 1 Instantiation in , therefore , Should be determined by the 2 Sending signal , stay 1 Receive signals and process （ hide 2 Show 1）.
4. If in 1 Instantiation in 2, That must be in 1 Add 2 The header file .

scene ：

No matter how many forms are switched, the idea is the same , From front to back , Instantiate the following form object , And display ; From back to front , Sending signal , Handled by the previous form .

Code ：

Created three Qt The interface class represents three forms respectively , Post the code as follows ：
oneForm.h Code

#ifndef ONEFORM_H
#define ONEFORM_H
#include <QWidget>
#include <twoform.h>
QT_BEGIN_NAMESPACE
namespace Ui {
     class oneForm; }
QT_END_NAMESPACE
class oneForm : public QWidget
{
    
    Q_OBJECT
public:
    oneForm(QWidget *parent = nullptr);
    ~oneForm();
    twoForm t1;// Global instantiation 2 No. form 
    void doProcessGoToTwoForm();// Show 2, hide 1
    void doProcessTwoFormRequst();// receive 2 The signal , Show 1
private:
    Ui::oneForm *ui;
};
#endif // ONEFORM_H

oneForm.cpp Code

#include "oneform.h"
#include "ui_oneform.h"
oneForm::oneForm(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::oneForm)
{
    
    ui->setupUi(this);
    connect(ui->btn1,&QPushButton::clicked,this,&oneForm::doProcessGoToTwoForm);// Switch to the second interface 
    connect(&t1,&twoForm::backToOne,this,&oneForm::doProcessTwoFormRequst);// The received signal displays the first interface 
}
oneForm::~oneForm()
{
    
    delete ui;
}
void oneForm::doProcessGoToTwoForm()
{
    
// The first way   effect ： The window flashed by , Create local variables , End of slot function execution , The system reclaims memory space 
// twoForm t2;
// t2.show();
// The second way   Pointer to the variable   effect ： Specifies that the parent object is the current object , The window will be attached to the current window 
// twoForm *t3 = new twoForm(this);
// t3->show();
// The third way , Pointer to the variable   effect ： One button per click , A new pointer variable will be created , Multiple forms will appear 
// twoForm * t4 = new twoForm();
// t4->show();
// The fourth way , Create global pointer variables or class objects 
        t1.show();
        this->hide();
}

void oneForm::doProcessTwoFormRequst()
{
    
    this->show();
}

twoForm.h Code

#ifndef TWOFORM_H
#define TWOFORM_H
#include <QWidget>
#include <threeform.h>
namespace Ui {
    
class twoForm;
}
class twoForm : public QWidget
{
    
    Q_OBJECT
public:
    explicit twoForm(QWidget *parent = nullptr);
    ~twoForm();
    void doProcessBackToOneForm();// Send a signal to 1  hide 2
    void doProcessGoToThreeForm();// hide 2  Show 3
    void doProcessThreeFormRequst();// receive 3 The signal , Show 2
    threeForm *t2;// Create a global 3 Form pointer variable No 
signals:
    void backToOne();
private:
    Ui::twoForm *ui;
};
#endif // TWOFORM_H

twoForm.cpp Code

#include "twoform.h"
#include "ui_twoform.h"
twoForm::twoForm(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::twoForm)
{
    
    ui->setupUi(this);
    t2 = new threeForm();
    connect(ui->btn2,&QPushButton::clicked,this,&twoForm::doProcessBackToOneForm);// Return to the first interface by sending a signal 
    connect(ui->btn3,&QPushButton::clicked,this,&twoForm::doProcessGoToThreeForm);// Switch to the third interface 
    connect(t2,&threeForm::backToTwo,this,&twoForm::doProcessThreeFormRequst);// Display the second interface by processing the signal 
}

twoForm::~twoForm()
{
    
    delete ui;
}
void twoForm::doProcessBackToOneForm()
{
    
    emit backToOne();
    this->hide();
}
void twoForm::doProcessGoToThreeForm()
{
    
    this->hide();
    t2->show();
}
void twoForm::doProcessThreeFormRequst()
{
    
    this->show();
}

threeForm.h Code

#ifndef THREEFORM_H
#define THREEFORM_H
#include <QWidget>
namespace Ui {
    
class threeForm;
}
class threeForm : public QWidget
{
    
    Q_OBJECT
public:
    explicit threeForm(QWidget *parent = nullptr);
    ~threeForm();
    void doProcessBackToTwoForm();// Send a signal to 2
signals:
    void backToTwo();
private:
    Ui::threeForm *ui;
};
#endif // THREEFORM_H

threeForm.cpp Code

#include "threeform.h"
#include "ui_threeform.h"
threeForm::threeForm(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::threeForm)
{
    
    ui->setupUi(this);
    connect(ui->btn4,&QPushButton::clicked,this,&threeForm::doProcessBackToTwoForm);// towards 2 Sending signal 
}
threeForm::~threeForm()
{
    
    delete ui;
}
void threeForm::doProcessBackToTwoForm()
{
    
    this->hide();
    emit backToTwo();
}

effect