- PyQt Tutorial
- PyQt Useful Resources
Qt Signals And Slots Between Classes Near Me
- Selected Reading
One key and distinctive feature of Qt framework is the use of signals and slots to connect widgets and related actions. But as powerful the feature is, it may look compelling to a lot of developers not used to such a model, and it may take some time at the beginning to get used to understand how to use signals and slots properly. I have a class X with a slot, and a class Y with a signal. I'm setting up the connection from class X, and created a public method in class Y to emit the signal from class X (I'm not sure this step was necessary). Then, if I call that method from class X, signal is emitted, and slot is executed. A QObject only holds data and logic you can use in QML as properties, signals and slots. When registering a QObject class as a type for QML, keep this restriction in mind. To create a QML Item with C which should support a visual representation with all default properties, derive from QQuickItem instead.
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.
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 −