Slot Example Qt
- PyQt Tutorial
Widget.signal.connect(slotfunction) Suppose if a function is to be called when a button is clicked. Here, the clicked signal is to be connected to a callable function. It can be achieved in any of the following two techniques − QtCore.QObject.connect(button, QtCore.SIGNAL(“clicked”), slotfunction). The first example uses three separate handler functions, or slots, for each check box. The second example uses a single slot for all three check boxes. Follow the tutorial steps below to build the two QCheckBox example programs. Create a New Qt Widgets Application. Open Qt Creator and start a new Qt Widgets Application called checkbox. The good thing about this is that the subscriber (the slot side) doesn't need to care about details of the signal. It just needs to connect. Thus, here we have a great deal of loose coupling. You can change the buttons implementation, but the interface for the slots would still be the same. Look at Qt Signals/Slots or Boost Signals for more.
Looking through the Qt source it seems that when a slot is called from QMetaObject::invokeMethod the return type can be specified and the return value obtained. (Have a look at invokeMethod in the Qt help) I could not find many examples of this actually being used in the Qt source. One I found was. Bool QAbstractItemDelegate::helpEvent.
- PyQt Useful Resources
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Unlike a console mode application, which is executed in a sequential manner, a GUI based application is event driven. Functions or methods are executed in response to user’s actions like clicking on a button, selecting an item from a collection or a mouse click etc., called events.
Qt Virtual Slot
Widgets used to build the GUI interface act as the source of such events. Each PyQt widget, which is derived from QObject class, is designed to emit ‘signal’ in response to one or more events. The signal on its own does not perform any action. Instead, it is ‘connected’ to a ‘slot’. The slot can be any callable Python function.
In PyQt, connection between a signal and a slot can be achieved in different ways. Following are most commonly used techniques −
A more convenient way to call a slot_function, when a signal is emitted by a widget is as follows −
Suppose if a function is to be called when a button is clicked. Here, the clicked signal is to be connected to a callable function. It can be achieved in any of the following two techniques −
or
Example
In the following example, two QPushButton objects (b1 and b2) are added in QDialog window. We want to call functions b1_clicked() and b2_clicked() on clicking b1 and b2 respectively.
When b1 is clicked, the clicked() signal is connected to b1_clicked() function
When b2 is clicked, the clicked() signal is connected to b2_clicked() function
Example
The above code produces the following output −