- PyQt5 Tutorial
- PyQt5 Useful Resources
PyQt5 uses a unique signal and slot mechanism to handle events. Signals and slots are used for communication between objects, and when a particular event occurs, the signal is fired. The slot can be any Python call. The connection to the slot is called while the signal is transmitting. PyQt5 signals and slots Graphical applications (GUI) are event-driven, unlike console or terminal applications. A users action like clicks a button or selecting an item in a list is called an event. If an event takes place, each PyQt5 widget can emit a signal.
- Selected Reading
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.
Pyqt Signal Slot Emit Sensor
Using Qt Designer's Signal/Slot Editor
First design a simple form with a LineEdit control and a PushButton.
It is desired that if button is pressed, contents of text box should be erased. The QLineEdit widget has a clear() method for this purpose. Hence, the button's clicked signal is to be connected to clear() method of the text box.
To start with, choose Edit signals/slots from Edit menu (or press F4). Then highlight the button with mouse and drag the cursor towards the textbox
As the mouse is released, a dialog showing signals of button and methods of slot will be displayed. Select clicked signal and clear() method
The Signal/Slot Editor window at bottom right will show the result −
Save ui and Build and Python code from ui file as shown in the below code −
Generated Python code will have the connection between signal and slot by the following statement −
Run signalslot.py and enter some text in the LineEdit. The text will be cleared if the button is pressed.
Building Signal-slot Connection
Instead of using Designer, you can directly establish signal-slot connection by following syntax −
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 technique −
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.
- PyQt5 Tutorial
- PyQt5 Useful Resources
PyQt5 uses a unique signal and slot mechanism to handle events. Signals and slots are used for communication between objects, and when a particular event occurs, the signal is fired. The slot can be any Python call. The connection to the slot is called while the signal is transmitting. PyQt5 signals and slots Graphical applications (GUI) are event-driven, unlike console or terminal applications. A users action like clicks a button or selecting an item in a list is called an event. If an event takes place, each PyQt5 widget can emit a signal.
- Selected Reading
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.
Pyqt Signal Slot Emit Sensor
Using Qt Designer's Signal/Slot Editor
First design a simple form with a LineEdit control and a PushButton.
It is desired that if button is pressed, contents of text box should be erased. The QLineEdit widget has a clear() method for this purpose. Hence, the button's clicked signal is to be connected to clear() method of the text box.
To start with, choose Edit signals/slots from Edit menu (or press F4). Then highlight the button with mouse and drag the cursor towards the textbox
As the mouse is released, a dialog showing signals of button and methods of slot will be displayed. Select clicked signal and clear() method
The Signal/Slot Editor window at bottom right will show the result −
Save ui and Build and Python code from ui file as shown in the below code −
Generated Python code will have the connection between signal and slot by the following statement −
Run signalslot.py and enter some text in the LineEdit. The text will be cleared if the button is pressed.
Building Signal-slot Connection
Instead of using Designer, you can directly establish signal-slot connection by following syntax −
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 technique −
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.
Pyqt Signal Slot Emit Meter
When b1 is clicked, the clicked() signal is connected to b1_clicked() function −
Pyqt Signal Slot Emit Generator
When b2 is clicked, the clicked() signal is connected to b2_clicked() function.
The above code produces the following output −
Pyqt Signal Slot Emit Light
Output
