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<HTML
><HEAD
><TITLE
>Signal and Slot Support</TITLE
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><H1
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><A
NAME="AEN81"
></A
>Signal and Slot Support</H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN83"
></A
>General Signals and Slots</H2
><P
>A signal may be either a Qt signal (specified using
<TT
CLASS="LITERAL"
>TQT_SIGNAL()</TT
>) or a Python signal (specified using
<TT
CLASS="LITERAL"
>PYQT_SIGNAL()</TT
>).</P
><P
>A slot can be either a Python callable object, a Qt signal (specified using
<TT
CLASS="LITERAL"
>TQT_SIGNAL()</TT
>), a Python signal (specified using
<TT
CLASS="LITERAL"
>PYQT_SIGNAL()</TT
>), or a Qt slot (specified using
<TT
CLASS="LITERAL"
>TQT_SLOT()</TT
>).</P
><P
>You connect signals to slots (and other signals) as you would from C++. For
example:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>TQObject.connect(a,TQT_SIGNAL("QtSig()"),pyFunction)
TQObject.connect(a,TQT_SIGNAL("QtSig()"),pyClass.pyMethod)
TQObject.connect(a,TQT_SIGNAL("QtSig()"),PYQT_SIGNAL("PySig"))
TQObject.connect(a,TQT_SIGNAL("QtSig()"),TQT_SLOT("QtSlot()"))
TQObject.connect(a,PYQT_SIGNAL("PySig"),pyFunction)
TQObject.connect(a,PYQT_SIGNAL("PySig"),pyClass.pyMethod)
TQObject.connect(a,PYQT_SIGNAL("PySig"),TQT_SIGNAL("QtSig()"))
TQObject.connect(a,PYQT_SIGNAL("PySig"),TQT_SLOT("QtSlot()"))</PRE
></TD
></TR
></TABLE
><P
>When a slot is a Python method that corresponds to a Qt slot then a signal can
be connected to either the Python method or the Qt slot. The following
connections achieve the same effect.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>sbar = TQScrollBar()
lcd = TQLCDNumber()
TQObject.connect(sbar,TQT_SIGNAL("valueChanged(int)"),lcd.display)
TQObject.connect(sbar,TQT_SIGNAL("valueChanged(int)"),lcd,TQT_SLOT("display(int)"))</PRE
></TD
></TR
></TABLE
><P
>The difference is that the second connection is made at the C++ level and is
more efficient.</P
><P
>Disconnecting signals works in exactly the same way.</P
><P
>Any instance of a class that is derived from the <TT
CLASS="LITERAL"
>TQObject</TT
>
class can emit a signal using the <TT
CLASS="LITERAL"
>emit</TT
> method. This takes
two arguments. The first is the Python or Qt signal, the second is a Python
tuple which are the arguments to the signal. For example:</P
><TABLE
BORDER="0"
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WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>a.emit(TQT_SIGNAL("clicked()"),())
a.emit(PYQT_SIGNAL("pySig"),("Hello","World"))</PRE
></TD
></TR
></TABLE
><P
>Qt allows a signal to be connected to a slot that requires fewer arguments than
the signal passes. The extra arguments are quietly discarded. Python slots
can be used in the same way.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN103"
></A
>Slots in Menus, Toolbars and Actions</H2
><P
>The C++ declarations for menu items or KActions are similar to these examples:</P
><TABLE
BORDER="0"
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WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>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 )</PRE
></TD
></TR
></TABLE
><P
>Notice the "const TQObject* receiver, const char* slot" parameters for each declaration.</P
><P
>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
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>p = insertItem ("Open", self.slotOpen, 0, -1, -1)
action = KAction ("Open", 0, self.slotOpen, None, 0)</PRE
></TD
></TR
></TABLE
><P
>This substitution applies to appropriate methods in KStdAction, KAction and related
subclasses, KAccelMenu and KToolBar</P
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