- Qt Signal Slot Connect Lambda
- Qt Signal Slot Connect Disconnect
- Qt Signal Slot Direct Connection
- Qt Check Signal Slot Connection
- Qt Remove Signal Slot Connection
I found out today that Qt's slots/signals architecture is even better than I thought. Normally, developers connect widget signals to widget slots to be notified of events. Today I discovered that signals can actually be connected to other signals, which saved me from writing some really stupid code This may seem weird, but consider this. QObject::connect(object2, SIGNAL(b), receiver, SLOT(slot)); QObject::connect(object3, SIGNAL(c), receiver, SLOT(slot));@ Now I want a function to disconnect all the signals from receiver's slot. There is an option: @QObject::disconnect(receiver, SLOT(slot));@ but this connects only the signals in the current object.
This page describes the use of signals and slots in Qt for Python.The emphasis is on illustrating the use of so-called new-style signals and slots, although the traditional syntax is also given as a reference.
The main goal of this new-style is to provide a more Pythonic syntax to Python programmers.
- 2New syntax: Signal() and Slot()
Traditional syntax: SIGNAL () and SLOT()
QtCore.SIGNAL() and QtCore.SLOT() macros allow Python to interface with Qt signal and slot delivery mechanisms.This is the old way of using signals and slots.
The example below uses the well known clicked signal from a QPushButton.The connect method has a non python-friendly syntax.It is necessary to inform the object, its signal (via macro) and a slot to be connected to.
New syntax: Signal() and Slot()
The new-style uses a different syntax to create and to connect signals and slots.The previous example could be rewritten as:
Using QtCore.Signal()
Signals can be defined using the QtCore.Signal() class.Python types and C types can be passed as parameters to it.If you need to overload it just pass the types as tuples or lists.
In addition to that, it can receive also a named argument name that defines the signal name.If nothing is passed as name then the new signal will have the same name as the variable that it is being assigned to.
The Examples section below has a collection of examples on the use of QtCore.Signal().
Note: Signals should be defined only within classes inheriting from QObject.This way the signal information is added to the class QMetaObject structure.
Using QtCore.Slot()
Slots are assigned and overloaded using the decorator QtCore.Slot().Again, to define a signature just pass the types like the QtCore.Signal() class.Unlike the Signal() class, to overload a function, you don't pass every variation as tuple or list.Instead, you have to define a new decorator for every different signature.The examples section below will make it clearer.
Another difference is about its keywords.Slot() accepts a name and a result.The result keyword defines the type that will be returned and can be a C or Python type.name behaves the same way as in Signal().If nothing is passed as name then the new slot will have the same name as the function that is being decorated.
Examples
The examples below illustrate how to define and connect signals and slots in PySide2.Both basic connections and more complex examples are given. Legal gambling age in wisconsin.
- Hello World example: the basic example, showing how to connect a signal to a slot without any parameters.
- Next, some arguments are added. This is a modified Hello World version. Some arguments are added to the slot and a new signal is created.
- Add some overloads. A small modification of the previous example, now with overloaded decorators.
- An example with slot overloads and more complicated signal connections and emissions (note that when passing arguments to a signal you use '[]'):
- An example of an object method emitting a signal:
Qt Signal Slot Connect Lambda
- An example of a signal emitted from another QThread:
- Signals are runtime objects owned by instances, they are not class attributes:
Quite a frequent problem when working with signals with slots in Qt5, according to my observations on the forum, is the connection of slots in the syntax on the pointers to signals having an overload of the signature. The same applies to slots that have an overload.
Let's take a test class that has overloaded signals.
Qt Signal Slot Connect Disconnect
Here there is a signal, with an overload of the signature. Connect this signal will also be to the slots that are declared in the Widget class, and which also have an overload of the signature.
How it was in Qt4
Within Qt4, everything was solved quite simply by specifying the signature of the signal and the slot in the SIGNAL and SLOT macros.
How it became in Qt5
But in Qt5, when writing in the new syntax of signals and slots, there are some problems. Because you need to make the static_cast of the method signature.
By the way, the new syntax also allows you to connect signals to slots with a smaller signature, as it was in Qt4.
Qt Signal Slot Direct Connection
Advantages of the new syntax
And now a stumbling block. Why use the new syntax of signals and slots? I still hear this question from time to time. Especially when people see such terrible castes of signatures.
Qt Check Signal Slot Connection
- Therefore, I will list potential advantages:The ability to track errors in the connection of signals and slots at the compilation stage, rather than in the runtime
- Reducing compilation time by excluding macros from the code
- The ability to connect lambda functions, it's quite an important bun
- We protect ourselves from errors when we try to connect from the outside to a private slot. Yes!! Yes!! The SIGNAL and SLOT macros ignore the access levels of methods, violating OOP.
Qt Remove Signal Slot Connection
In general, for me this is enough, but for you?
