Thursday, June 13, 2013

Adding a custom slot in Qt Designer and Visual Studio 2012

I was going through the "Getting started" section for Qt using VS2012 as my IDE, and I got stuck when I had to add a slot to a button.  Apparently there is a bug when using the Visual Studio add-in, that the submenu Go to slot doesn't show up in a context menu in Qt Designer (see bug).  Needless to say, I spent more than two hours trying to figure out how to get around this problem.  The following is what I found:

Let's say you have a class called Notepad that has a quit button and you want to handle when the button is clicked.  First create a private slot in the class definition in the header file - Notepad.h in this example.

class Notepad : public QMainWindow
{
...

private slots:
    public void on_quitButton_clicked();

...
}

On the Notepad.cpp add the following:

void Notepad::on_quitButton_clicked();
{
}

Note: from what I read it's good idea to follow the convention on_name_signal() for all your custom slots.

Now open your *.ui file with Qt Designer.  At this point I tried using the Signal/Slot editor to add the slot to the button on the GUI.  The "custom" slot we wrote above however doesn't show up when you click the slot dropdown.


After scouring stackoverflow and the Qt forums I found a couple of ways to get the custom slot to show in the dropdown.

  1. Go to Signal/Slots mode by pressing F4 on your keyboard.
  2. Click on the button so that it changes color.
  3. Left-click and drag it to the top of the main window.

    4.  This brings up the Configure Connection window
    5.  On the left pane select the Signal clicked()
    6.  On the right pane select Edit
    7.  This brings yet another window, select the + button.
    8.  Enter the name of the custom slot, on_quitButton_clicked() in this case.
    9.  Click Ok and now you should be able to see the slot in the dropdown in Signal/Slot editor.



Pretty tedious, but if you want to use Visual Studio as the IDE, this is what you will have to go through until someone fixes the bug, or you decide to use Qt Creator.  If I keep finding issues like this by using Visual Studio I think I'll have to do to the latter.

5 comments:

Anonymous said...

Thanks, I had exactly the same problem and your solution works perfectly for me. I don't understand why one has to use a workaround for such basic things in GUI programming.

Anonymous said...

Thanks. I'm new to Qt and attempting to use it in a Visual Studio project. I have yet to find much of anything written about using Qt this way and what is there seems old or incorrect. So far my opinion of Qt isn't very high. Things just don't seem to work.

Unknown said...
This comment has been removed by the author.
Anonymous said...

thank you so much !! friend from China-Ajiang.

Jose said...

I don't know if anyone is using Qt this way, but now that I have years of experience to work with Qt, I would say don't use Visual Studio. Stick with Qt Creator if you want to build applications with Qt.