Qt Slot Derived Class

• Qt No Such Slot In Derived Class
• Qt Slot Derived Classes

QDBusAbstractAdaptor uses the standard QObject mechanism of signals, slots and properties to determine what signals, methods and properties to export to the bus. Any signal emitted by QDBusAbstractAdaptor-derived classes will be automatically be relayed through any D-Bus connections the object is registered on. 1 import sys 2 from PySide2.QtWidgets import QApplication, QPushButton 3 from PySide2.QtCore import QObject, Signal, Slot 4 5 app = QApplication (sys. Argv) 6 7 # define a new slot that receives a C 'int' or a 'str' 8 # and has 'saySomething' as its name 9 @Slot (int) 10 @Slot (str) 11 def saysomething (stuff): 12 print (stuff) 13 14 class. QWidget class, derived from QObject and QPaintDevice classes is the base class for all user interface objects. QDialog and QFrame classes are also derived from QWidget class. They have their own sub-class system. Here is a select list of frequently used widgets.

Introduction

If I instantiate a new instance of the derived class.aTestslot seems to be populated in the method because I can print it out, viz An object of class 'OPAppt' Slot 'ClinicName': 1 'Unknown' Slot 'EventName': 1 'An Event'. Qt's signals and slots mechanism does not require classes to have knowledge of each other, which makes it much easier to develop highly reusable classes. Since signals and slots are type-safe, type errors are reported as warnings and do not cause crashes to occur. For example, if a Quit button's clicked signal is connected to the application.

Remember old X-Windows call-back system? Generally it isn't type safe and flexible. There are many problems with them. Qt offers a new event handling system: signal-slot connections. Imagine an alarm clock. When alarm is ringing, a signal is being sent (emit). And you're handling it in a slot.

• Every QObject class may have as many signals and slots as you want
• You can emit signals only from within that class, where the signal is located
• You can connect signal with another signal (make chains of signals);
• Every signal and slot can have unlimited count of connections with other.
• ATTENTION! You can't set default value in slot attributes e.g. void mySlot(int i = 0);

Connection

You can connect signal with this template:

QObject::connect (

);

You have to wrap const char * signal and const char * method into SIGNAL() and SLOT() macros.

And you also can disconnect signal-slot:

QObject::disconnect (

);

Deeper

Widgets emit signals when events occur. For example, a button will emit a clicked signal when it is clicked. A developer can choose to connect to a signal by creating a function (a slot) and calling the connect() function to relate the signal to the slot. Qt's signals and slots mechanism does not require classes to have knowledge of each other, which makes it much easier to develop highly reusable classes. Since signals and slots are type-safe, type errors are reported as warnings and do not cause crashes to occur.

For example, if a Quit button's clicked() signal is connected to the application's quit() slot, a user's click on Quit makes the application terminate. In code, this is written as

connect(button, SIGNAL (clicked()), qApp, SLOT (quit()));

Connections can be added or removed at any time during the execution of a Qt application, they can be set up so that they are executed when a signal is emitted or queued for later execution, and they can be made between objects in different threads.

The signals and slots mechanism is implemented in standard C++. The implementation uses the C++ preprocessor and moc, the Meta Object Compiler, included with Qt. Code generation is performed automatically by Qt's build system. Developers never have to edit or even look at the generated code.

In addition to handling signals and slots, the Meta Object Compiler supports Qt's translation mechanism, its property system, and its extended runtime type information. It also makes runtime introspection of C++ programs possible in a way that works on all supported platforms.

To make moc compile the meta object classes don't forget to add the Q_OBJECT macro to your class.

The following are the built-in features of the PythonQt library:

• Access all slots, properties, children and registered enums of any QObject derived class from Python
• Connecting Qt Signals to Python functions (both from within Python and from C++)
• Easy wrapping of Python objects from C++ with smart, reference-counting PythonQtObjectPtr.
• Convenient conversions to/from QVariant for PythonQtObjectPtr.
• Wrapping of C++ objects (which are not derived from QObject) via PythonQtCppWrapperFactory
• Extending C++ and QObject derived classes with additional slots, static methods and constructors (see Decorators)
• StdOut/Err redirection to Qt signals instead of cout
• Interface for creating your own import replacement, so that Python scripts can be e.g. signed/verified before they are executed (PythonQtImportFileInterface)
• Mapping of plain-old-datatypes and ALL QVariant types to and from Python
• Support for wrapping of user QVariant types which are registerd via QMetaType
• Support for Qt namespace (with all enumerators)
• All PythonQt wrapped objects support the dir() statement, so that you can see easily which attributes a QObject, CPP object or QVariant has
• No preprocessing/wrapping tool needs to be started, PythonQt can script any QObject without prior knowledge about it (except for the MetaObject information from the moc)
• Multiple inheritance for C++ objects (e.g. a QWidget is derived from QObject and QPaintDevice, PythonQt will automatically cast a QWidget to a QPaintDevice when needed)
• Polymorphic downcasting (if e.g. PythonQt sees a QEvent, it can downcast it depending on the type(), so the Python e.g. sees a QPaintEvent instead of a plain QEvent)
• Deriving C++ objects from Python and overwriting virtual method with a Python implementation (requires usage of wrapper generator or manual work!)
• Extensible handler for Python/C++ conversion of complex types, e.g. mapping of QVector<SomeObject> to/from a Python array
• Setting of dynamic QObject properties via setProperty(), dynamic properties can be accessed for reading and writing like normal Python attributes (but creating a new property needs to be done with setProperty(), to distinguish from normal Python attributes)
• Support for QtCore.Signal, QtCore.Slot and QtCore.Property, including the creation of a dynamic QMetaObject.

PythonQt offers the additional PythonQt_QtAll library which wraps the complete Qt API, including all C++ classes and all non-slots on QObject derived classes. This offers the following features:

• Complete Qt API wrapped and accessible
• The following modules are available as submodules of the PythonQt module:
  • QtCore
  • QtGui
  • QtNetwork
  • QtOpenGL
  • QtSql
  • QtSvg
  • QtWebKit
  • QtXml
  • QtXmlPatterns
  • QtMultimedia
  • QtQml
  • QtQuick
• Any Qt class that has virtual methods can be easily derived from Python and the virtual methods can be reimplemented in Python
• Polymorphic downcasting on QEvent, QGraphicsItem, QStyleOption, ...
• Multiple inheritance support (e.g., QGraphicsTextItem is a QObject and a QGraphicsItem, PythonQt will handle this well)
• QtQuick support is experimental and currently it is not possible to register new qml components from Python

PythonQt supports:

Qt No Such Slot In Derived Class

• Python 2 (>= Python 2.6)
• Python 3 (>= Python 3.3)
• Qt 4.x (Qt 4.7 and Qt 4.8 recommended)
• Qt 5.x (Tested with Qt 5.0, 5.3, 5.4 and 5.6)

The last working Qt4 version is available at svn branches/Qt4LastWorkingVersion or you can download the PythonQt 3.0 release. The current svn trunk no longer supports Qt4, since we started to make use of some Qt5-only features.

Qt Slot Derived Classes

• PythonQt is not as pythonic as PySide in many details (e.g. buffer protocol, pickling, translation support, ...) and it is mainly thought for embedding and intercommunication between Qt/Cpp and Python
• PythonQt offers properties as Python attributes, while PySide offers them as setter/getter methods (e.g. QWidget.width is a property in PythonQt and a method in PySide)
• PythonQt currently does not support instanceof checks for Qt classes, except for the exact match and derived Python classes
• QObject.emit to emit Qt signals from Python is not yet implemented but PythonQt allows to just emit a signal by calling it like a normal slot
• Ownership handling of objects is not as complete as in PySide and PySide, especially in situations where the ownership is not clearly passed to C++ on the C++ API.
• QStrings are always converted to unicode Python objects, QByteArray always stays a QByteArray and can be converted using QByteArray.data()
• Qt methods that take an extra 'bool* ok' parameter can be called passing PythonQt.BoolResult as parameter. In PySide, a tuple is returned instead.