It's perfectly acceptable to connect the slot twice or even more times but when the signal gets fired your slot will be called for each connection you made which is probably not what you want. Note that it is not necessarily wrong to have multiple connections. There are (probably) perfectly valid uses for it. How Does it Work? Compare the signature string to see if the arguments match Use the information provided my the moc to nd the index of the signal and of the slot.
Overview
Qt Connect Signal Slot Twice Free
This program demonstrates how QML and C++ can be connected through Qt signalsand slots. It does this through embedding C++ code as a context property in QMLrather than explicitly connecting signals and slots.
When the program is started, the C++ part send a signal to QML, including aparameter. This signal is only sent once. When the user clicks on the windowarea, a signal is sent from QML to a C++ slot.
Watch the console output to see if it works.
Installation
This program requires a working Qt5 installation. It was tested with version 5.3 and 5.4.
In order to compile and run the program, execute the following commands.
Alternatively, the project can be loaded into Qt Creator and started from there.
More Documentation
This source code belongs to an article on our website.
- PyQt Tutorial
- PyQt Useful Resources
- 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.
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
Signal And Slot
The above code produces the following output −