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c++qt
Donald Duck
Donald Duck

Reputation: 8892

Put arguments in slots in Qt

I've made a class named MyWindow which inherits from QWidget to create a window. Here is the content of mywindow.h:

class MyWindow: public QWidget{
    public:
        MyWindow(QString title,QString icon,int w = 600,int h = 400);
        int getWidth() const;
        int getHeight() const;
    public slots:
        void openDialogBox(QString title,QString message);
    private:
        int m_width;
        int m_height;
};

There is a openDialogBox slot which takes the title and the message of the dialog box as arguments.

I've made a menu bar which basically looks like this:

MyWindow myWindow("Example window",QCoreApplication::applicationDirPath() + "/icon.png");
QMenuBar menuBar(&myWindow);
menuBar.setGeometry(0,0,myWindow.getWidth(),menuBar.geometry().height());
QMenu *fileMenu = new QMenu("&File");
QAction *fileMenu_open = fileMenu->addAction("&Open");
MyWindow::connect(fileMenu_open,&QAction::triggered,&myWindow,&MyWindow::openDialogBox);

In the last line, I would like to send arguments to the slot &MyWindow::openDialogBox. I tried to do:

MyWindow::connect(fileMenu_open,&QAction::triggered,&myWindow,&MyWindow::openDialogBox("Title","Hello, this is a message"));

but it didn't work (I don't need you to explain why it didn't work, I already know why). How to do this properly so that it works?

Upvotes: 0

Views: 63

Answers (2)

Mike
Mike

Reputation: 8355

Since you are using the New Signal Slot Syntax, I would suggest using a c++11 lambda instead of a slot, and call the desired function inside your slot, here is how your connect call would look like:

QObject::connect(fileMenu_open, &QAction::triggered, &myWindow, [&myWindow](){
    myWindow.openDialogBox("Title","Hello, this is a message");
});

Note that openDialogBox is not required to be a slot this way, it can be any normal function.

If your compiler does not support C++11 lambda expression, you might have to declare a slot that does not take any argument, and connect to that slot. And inside that slot call your function with the desired arguments. . .

Upvotes: 2

Random Coder 99
Random Coder 99

Reputation: 386

Use lambdas 

QObject::connect(fileMenu_open, &QAction::triggered, &myWindow, [QWeakPointer<MyWindow> weakWindow = myWindow]()
{
    weakWindow->openDialogBox("Title","Hello, this is a message");
});

QWeakPointer is used in case your class is moved, so the "old" myWindow is a dangling pointer
If your class won't be moved, just capture myWindow.
Note that my code needs C++14 to declare a variable in the lambda capture

Upvotes: 0

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