Signals and Slots. In Qt, we have an alternative to the callback technique: We use signals and slots. A signal is emitted when a particular event occurs. Qt's widgets have many predefined signals, but we can always subclass widgets to add our own signals to them. A slot is a function that is called in response to a particular signal. Usually, double clicking these presents a menu of objects/signals etc, but on latest QT Creator it's not working. A menu sometimes pops up, but if it does it immediately disappears. In this tutorial we will learn How to use signal and slots in qt. File-New File or Project Applications-Qt Gui Application-Choose We keep the class as MainWindow as given by default.
It would be possible to have the slots to which the resized and moved signals are connected check the new position or size of the circle and respond accordingly, but it's more convenient and requires less knowledge of circles by the slot functions if the signal that is sent can include that information.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
public void on_quitButton_clicked();
On the Notepad.cpp add the following:
Note: from what I read it's good idea to follow the convention on_name
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.
- Go to Signal/Slots mode by pressing F4 on your keyboard.
- Click on the button so that it changes color.
- 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.