I'm reading Rapid GUI Programming - Mark Summerfield with Python and QT
pg 131. Basically the mechanism is an event table which maps a 'signal'
to a 'function/slot' -correct?
self.connect(dial, SIGNAL("valueChanged(int)"), spinbox.setValue)
Here, dial.valueChanged -> spinbox.setValue
s.connect(w, SIGNAL("signalSignature"), functionName)
s.connect(w, SIGNAL("signalSignature"), instance.methodName)
s.connect(w, SIGNAL("signalSignature"), instance,
SLOT("slotSignature"))
Here, w.signalSignature -> functionName
-> instance.methodName
-> instance.slotSignature
If signalSignature is a C++ implemented thingy then we got to pass type
info as part of the mapping so "signalSignature(int, float, const char
*). PyQT signals are any type and any number of args..
If the Slot-function is implemented in C++ it's better to use the SLOT()
mechanism:
self.connect(dial, SIGNAL("valueChanged(int)"), spinbox,
SLOT("setValue(int)"))
Here, we are mapping dial.valueChanged(int) --> spinbox.setValue(int)
----
The part i found tricky was this:
class ZeroSpinBox(QSpinBox):
zeros = 0
def __init__(self, parent=None):
super(ZeroSpinBox, self).__init__(parent)
self.connect(self, SIGNAL("valueChanged(int)"), self.checkzero)
def checkzero(self):
if self.value() == 0:
self.zeros += 1
self.emit(SIGNAL("atzero"), self.zeros)
ZeroSpinBox.valueChanged -> ZeroSpinBox.checkzero? Why is he mapping
back to himself? Shouldn't it be widget-to-widget?
Then he raises a signal 'atzero' with one arg - the lack of a atzero()
implies it's a 'short-circuit' signal so self.zeroes is a python data
type. And in the book he says:
#######################
Here is how we connect to the signal in the form’s __init__() method:
zerospinbox = ZeroSpinBox()
...
self.connect(zerospinbox, SIGNAL("atzero"), self.announce)
Again, we must not use parentheses because it is a short-circuit signal.
And
for completeness, here is the slot it connects to in the form:
def announce(self, zeros):
print "ZeroSpinBox has been at zero %d times" % zeros
###########################
Whaaa...t?? Could someone explain what exactly is his grand design
besides being awfully circuitous? So he has some other Form thingy.. and
in that he sets up another mapping from ZeroSpinBox.atzero -->
ZeroSpinBox.announce ???? where's announce and atzero defined?
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