无法添加插槽并将其连接到按钮

Question

I gathered a code of an application called calendar from the base of examples of the Qt Framework. I am trying to learn from it and add there some functionality. The problem right now that I've got is that I want to implement two function to the two button that I created ( one for increase counting of the days and the second for decrease ).

The code that I added to the function for increasing the days is:

void MainWindow::forward(int *click_forward)
{
    click_forward++;
}

and the code added to the function for decreasing the days:

void MainWindow::backwards(int *click_backwards)
{
    click_backwards--; 
}

In the constructor I defined a variable named click which of the int
type, and I sent this variable to the both function by reference:

   forward(&click);
   backward(&click);   

In the header file, in the public slosts area these both functions are
defined as:

   void forward(int *click_forward);

   void backwards(int *click_backwards);

I also implemented two SIGNAL-SLOT connections:

   QObject::connect(nextbtn, SIGNAL(clicked()), this, SLOT(forward(int  
   &click)));

   QObject::connect(beforebtn, SIGNAL(clicked()), this, 
   SLOT(backwards(int &clickt))); 

But for some reasons when I compile the project I receive an information that:

   QObject::connect: No such slot MainWindow::forward(int &click) 

   QObject::connect: No such slot MainWindow::backwards(int &clickt)

I wanted to use pointers in these two functions, just to work on the original variable itself not on the copy. Could I please ask you to point me out what I am doing wrong.

Thank you,

Answer 1

The problem is that your signal and slot(s) have different signatures: signal has no arguments, but slot has an argument of pointer type. Besides, even if your signals connections would work, the execution of such code wouldn't do anything useful (at least) as you modify the temporary defined variables click_backwards etc.

I would solve this in the following way:

Define the class member variables and slots:

class MainWindow
{
    [..]
private slots:
    void forward();
    void backwards();

private:
    int click_forward;
    int click_backwards;
}

Define slots:

void MainWindow::forward()
{
    click_forward++;
}

void MainWindow::backwards()
{
    click_backwards--; 
}

And finally establish connections:

QObject::connect(nextbtn, SIGNAL(clicked()), this, SLOT(forward()));
QObject::connect(beforebtn, SIGNAL(clicked()), this, SLOT(backwards())); 

Answer 2

如果您这样处理信号和插槽，则会收到编译器错误而不是运行时错误，我个人认为这非常有帮助，因为它只会告诉您由于信号/插槽不兼容而导致它们无法连接

QObject::connect(nextbtn, &QPushButton::clicked, this, &MainWindow::forward);

Answer 3

By the way, you're not increasing the value of the integer, you're increasing the pointer.

That's a bug waiting to happen.