Linking a QWidget to another QWidget new created - c++

Question

I am try to, by pressing a button in the main QWidget, to create a new QWidget. In that new created QWidget I want to have a button connected to a slot of the main QWidget.
class UI : public QWidget
{
public:
UI(){connection();};
private:
QPushButton* all = new QPushButton{ "ALL" };
void connection(){
QObject::connect(all,QPushButton::clicked,[](){
SmallGUI* s=new SmallGUI{};
s->show();
});
}
void something(){
//something
}
and the second class
class SmallGUI1 :
public QWidget
{
public:
SmallGUI(){connection();};
private:
QPushButton* N =new QPushButton;
void connection(){
//to connect N to something()
}
I want to connect N to something() .

Answer 1

Before we start, there are some other problems with you code.
Note that in your second class, the constructor is not named the same as the class, which will cause some... Problems.
You also forgot to put a parent for your buttons (which may thus cause some unexpected results) AND for your Widgets (which is again not a good idea).
So, that being said, let us get to the main topic.
I tend to only put prototypes and declare the attributes in the .h file to make the code clearer, but you may of course adapt it to your needs or to your own programming convention.
There are several ways to do something like this, but the simplest one should look like this :
SmallGUI1.h :
#include "UI.h" //The file in which the class UI is declared
//OR :
//class UI; //If you need to include this file in UI.h
class SmallGUI1 : public QWidget{
Q_OBJECT //Q_OBJECT macro, check the doc for more explainations about it
public:
explicit SmallGUI1(UI *parent = nullptr); //Explicit means that this constructor cannot be used for implicit casts
~SmallGUI1();//Destructor needed because I only put the constructor above
private:
QPushButton* N; //Not very good looking to initialize attributes in the .h in my opinion, but works fine.
}
SmallGUI1.cpp :
SmallGUI1::SmallGUI1(UI *parent) : QWidget(parent){
N = new QPushButton(tr("Some text on the button") , this); //tr to enable translation on this string
//************* If I understood your question correctly, this is what you are looking for *************
connect(N , &QPushButton::clicked , parent , &UI::doSomething); //Select the signal you want
/*
Some code here
*/
show();
}
SmallGUI1::~SmallGUI1(){qDeleteAll(children());}
UI.h :
class UI : public QWidget{
Q_OBJECT
public:
explicit UI(QWidget *parent = nullptr);
~UI();
private:
QPushButton* all;
private slots :
void createSmallGUI1();
void doSomething();
}
UI.cpp :
#include "SmallGUI1.h"
UI::UI(QWidget *parent) : QWidget(parent){
all = new QPushButton(tr("ALL") , this);
connect(all , &QPushButton::clicked , this , &UI::createSmallGUI1);
/*
Some code here
*/
}
UI::~UI(){qDeleteAll(children());}
void UI::createSmallGUI1(){SmallGUI1 *gui = new SmallGUI1(this);}
void UI::doSomething(){
/*
Clever code here
*/
}

Answer 2

You can define the second widget as a child of the main widget to make things easier:
class UI : public QWidget {
...
private:
SmallGUI* s;
...
and then initialize it in the UI constructor, along with your all button. You can initially hide the child widget or disable it:
UI() {
all = new QPushButton{"ALL", this};
setWindowTitle("UI"); // just for clarification
s = new SmallGUI(this);
s->hide();
connection();
};
and 'show' it with button clicked signal
connect(all, &QPushButton::clicked, s, &SmallGUI::show);
Doing so gives you the option to connect the clicked signal of your N button to the something function in the parent class
connect(s->N, &QPushButton::clicked, this, &UI::something);
The complete program would be as follows,
#include <QApplication>
#include <QMessageBox>
#include <QPushButton>
#include <QWidget>
class SmallGUI : public QWidget {
public:
SmallGUI(QWidget* parent) : QWidget(parent) {
N = new QPushButton{"btn2", this};
connection();
};
QPushButton* N;
private:
void connection(){};
};
class UI : public QWidget {
public:
UI() {
all = new QPushButton{"ALL", this};
setWindowTitle("UI"); // just for clarification
s = new SmallGUI(this);
s->hide();
connection();
};
private:
SmallGUI* s;
QPushButton* all;
void connection() {
connect(all, &QPushButton::clicked, s, &SmallGUI::show);
connect(s->N, &QPushButton::clicked, this, &UI::something);
}
void something() { QMessageBox::information(this, "Hello", "Hello"); }
};
int main(int argc, char* argv[]) {
QApplication a(argc, argv);
UI w;
w.show();
return a.exec();
}

Answer 3

It is not good idea to connect to parent's slots from "nested" class, since SmallGUI1 will be tied to class UI.
Here is better solution, I think:
class UI : public QWidget
{
public:
UI(){connection();};
private:
QPushButton* all = new QPushButton{ "ALL" };
void connection(){
QObject::connect(all,QPushButton::clicked,[](){
SmallGUI1* s=new SmallGUI1;
connect(s,&USmallGUI1::button_clicked,this,&UI::something);
s->show();
});
}
void something(){
//something
}
And SmallGUI1 class:
class SmallGUI1 :
public QWidget
{
public:
SmallGUI1(){connection();};
signals:
void button_clicked();
private:
QPushButton* N;
void connection(){
//to connect N to something()
N = new QPushButton;
connect(N,&QPushButton::clicked,this,&SmallGUI1::button_clicked)
}
This way, you are connecting QPusButton::clicked signal from SmallGUI1 to the signal SmallGUI1::button_clicked(). Dont need to implement additional slot, just connect signal to signal.
And in UI you are connecting button_clicked() signal to the slot dosomething()
DONT FORGET THE CONSTRUCTOR OF SmallGUI1! In your code, SmallGUI() will be just a method, which will not be called when SmallGUI1 is instantiated, and you have to call it by yourself.