CODEWITHSUNDEEP
qt
Royi Freifeld
Royi Freifeld

Reputation: 659

The proper way to design a GUI with Qt

I just started working with Qt, and I'm quite lost with the whole signal-slot system.
I understand the general concept, but I can't understand what is the proper way to design my GUI code. Is it supposed to be an hierarchy of classes holding pointers to each other? For example, if I have a main window, let's say W1, with button, B1, that should open another window, W2.
It's quite obvious why W1's class should hold a pointer to B1, but it seems that I need to hold pointer to W2's class, in order to connect B1's clicked() signal to some custom slot of W2, and I don't understand why... Isn't the signal-slot mechanism designed to be generic and not specific-instance-wise? What is the proper way of designing this example's code?

Upvotes: 2

Views: 363

Answers (2)

firescreamer
firescreamer

Reputation: 620

Connections are always created between instances of class. Signals and slots are mechanism to inform one instances of class B that there was a change or event in instances of class A.

Below is design of class W1 that will show window W2 when button B1 will be clicked. I skipped initialization of class W1, also getting button B1 because there are few ways to create UI of your window. I added check if connection was successful, just for safety (my habit).

class W1 :public QWidget
{
public:
A(QWidget *parent = 0):QWidget(parent)
{
   //init
   B1 = getB1();
   if(!connect(B1,SIGNAL(clicked()),this,SLOT(show_W2())))
       qFatal("%s %i connection failed B1->clicked this->show_W2",__FILE__,__LINE__);
}

public slots:
   void show_W2()
   {
      QWidget *W2 = new Window2(this->parent());
      //create window 
   }
protected:
    QPushButton *B1;
}

Here is different approach to your example, where class W1 don't now anything about class W2:

class W1 :public QWidget
{
public:
A(QWidget *parent = 0):QWidget(parent)
{
   //init
   B1 = getB1();
   if(!connect(B1,SIGNAL(clicked()),this,SIGNAL(B1_clicked())))
       qFatal("%s %i connection failed B1->clicked this->B1_clicked",__FILE__,__LINE__);
}

signals:
   B1_clicked()
}

void MainWindow::creatW1()
{
    W1 *_w1 = new W1;
    if(!connect(_w1,SIGNAL(B1_clicked()),this,SLOT(createW2())))
       qFatal("%s %i connection failed _w1->B1_clicked this->show_W2",__FILE__,__LINE__);
}

Upvotes: 1

arrowd
arrowd

Reputation: 34391

What is the proper way of designing this example's code?

Create a simple UI with Qt Designer and look at what it generates. That helped me a lot when i was starting with Qt.

Upvotes: 3

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