• PyQt Tutorial

Type-safe Signals and Slots in C: Part 2. A signal and you can combine the multiple return values from the slots into one single return value given back to the caller (if the return type is not void). Boost and QT also offer signal / slot functionality (see Part 1 of the article series). However, the signal slot.

• 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

The above code produces the following output −

Output

Connecting overloaded signals and slots in Qt 5 (3)

I'm having trouble getting to grips with the new signal/slot syntax (using pointer to member function) in Qt 5, as described in New Signal Slot Syntax. I tried changing this:

Qt Signal Slot Thread

to this:

but I get an error when I try to compile it:

error: no matching function for call to QObject::connect(QSpinBox*&, <unresolved overloaded function type>, QSlider*&, void (QAbstractSlider::*)(int))

I've tried with clang and gcc on Linux, both with -std=c++11.

What am I doing wrong, and how can I fix it?

Qt Signal Slot Parameter

Actually, you can just wrap your slot with lambda and this:

Qt Signal Slot Get Caller Id

will be look better. :