Signal and Slot Support

General Signals and Slots

A signal may be either a TQt signal (specified using SIGNAL()) or a Python signal (specified using PYSIGNAL()).

A slot can be either a Python callable object, a TQt signal (specified using SIGNAL()), a Python signal (specified using PYSIGNAL()), or a TQt slot (specified using SLOT()).

You connect signals to slots (and other signals) as you would from C++. For example:

TQObject.connect(a,SIGNAL("TQtSig()"),pyFunction)
TQObject.connect(a,SIGNAL("TQtSig()"),pyClass.pyMethod)
TQObject.connect(a,SIGNAL("TQtSig()"),PYSIGNAL("PySig"))
TQObject.connect(a,SIGNAL("TQtSig()"),SLOT("TQtSlot()"))
TQObject.connect(a,PYSIGNAL("PySig"),pyFunction)
TQObject.connect(a,PYSIGNAL("PySig"),pyClass.pyMethod)
TQObject.connect(a,PYSIGNAL("PySig"),SIGNAL("TQtSig()"))
TQObject.connect(a,PYSIGNAL("PySig"),SLOT("TQtSlot()"))

When a slot is a Python method that corresponds to a TQt slot then a signal can be connected to either the Python method or the TQt slot. The following connections achieve the same effect.

sbar = TQScrollBar()
lcd = TQLCDNumber()

TQObject.connect(sbar,SIGNAL("valueChanged(int)"),lcd.display)
TQObject.connect(sbar,SIGNAL("valueChanged(int)"),lcd,SLOT("display(int)"))

The difference is that the second connection is made at the C++ level and is more efficient.

Disconnecting signals works in exactly the same way.

Any instance of a class that is derived from the TQObject class can emit a signal using the emit method. This takes two arguments. The first is the Python or TQt signal, the second is a Python tuple which are the arguments to the signal. For example:

a.emit(SIGNAL("clicked()"),())
a.emit(PYSIGNAL("pySig"),("Hello","World"))

TQt allows a signal to be connected to a slot that retquires fewer arguments than the signal passes. The extra arguments are tquietly discarded. Python slots can be used in the same way.

Slots in Menus, Toolbars and Actions

The C++ declarations for menu items or KActions are similar to these examples:

int TQMenuData::insertItem (const TQString & text,
     const TQObject * receiver, const char * member,
     int accel = 0, int id = -1, int index = -1 )

KAction ( const TQString& text, int accel,
     const TQObject* receiver, const char* slot,
     TQObject* parent, const char* name = 0 )

Notice the "const TQObject* receiver, const char* slot" parameters for each declaration.

In PyKDE, these two parameters are replaced with a SINGLE parameter that specifies the slot to be connected to the menu item, toolbar button or KAction:

p = insertItem ("Open", self.slotOpen, 0, -1, -1)

action = KAction ("Open", 0, self.slotOpen, None, 0)

This substitution applies to appropriate methods in KStdAction, KAction and related subclasses, KAccelMenu and KToolBar