Qt connect and first connect or unicode

[Vincent Vande Vyvre]

Le 17/09/2013 11:05, Steven D'Aprano a écrit :
> On Tue, 17 Sep 2013 08:42:35 +0430, Mohsen Pahlevanzadeh wrote:
>
>> Dear all,
>>
>> Unfortunately, i confused and need help... the following code is:
>> ###################################################
>> ##CheckBox:
>>      QtCore.QObject.connect(self.checkBox,
>> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
>> self.materialsInstance.setFilterDict("C", self, "name",
>> self.lineEdit.text()))
>
> I don't use Qt, but I'll try to help.
>
> First question, what does _fromUtf8 do? It appears to be a private
> function. Is that your function? If you want to create a string from UTF-8
> bytes, use:
>
> some_bytes.decode('utf-8')
>
> I don't think there is a need for a dedicated _fromUtf8 function.
>
> If you are using Python 3, then "toggled(bool)" is already a Unicode
> string, and there is no need to convert from UTF-8.
>
> If you are using Python 2, then "toggled(bool)" is a byte string, and you
> can turn it into a Unicode string by just using the u prefix:
>
> u"toggled(bool)"
>
> Again, no need to convert from UTF-8.
>
> The only time you need to convert from UTF-8 is when you are reading data
> from a file, or other external source, that is encoded in UTF-8.
>
> Other than that, your first line of code seems like a straight-forward
> call to set a callback function. When the button is pressed, the
> instance's attribute materialsInstance calls the method setFilterDict.
>
>
>>          QtCore.QObject.connect(self.checkBox_2,
>> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
>> self.materialsInstance.setFilterDict("C", self, "bought_price",
>> persianToInteger(unicode(self.lineEdit_2.text()))))
> Again, the same method is called, only this time with different
> arguments. Hmmm, this strikes me as poor design. I think that a better
> design would be for the object to have a few methods:
>
>      def toggle_checkbox(self, flag):
>          # checkbox logic goes here, e.g.
>          if flag:
>              ...
>          else:
>              ...
>
> And then your callback is trivially
>
> lambda: self.toggle_checkbox(get_state)
>
>
> I'm not sure how to get the checkbox state from Qt, you will need to
> replace the "get_state" with the correct code.
>
> That, in my opinion, is easier to understand.
>
>
>>          QtCore.QObject.connect(self.checkBox_4,
>> QtCore.SIGNAL(_fromUtf8("toggled(bool)")), lambda:
>> self.materialsInstance.setFilterDict("C",self,"stock",
>> persianToInteger(unicode(self.lineEdit_3.text()))))
> And more callbacks. Most of your code is probably irrelevant to the
> problem you are having. You will help us to help you if you can read this
> website:
>
> http://sscce.org/
>
>
> and simplify your code.
>
>
> [...many more callbacks...]
>
>
>> ####################################################
>> Description:
>> I have 3 widget:
>> 1. CheckBox:  a. name b. bought_price c. stock 2. LineEdit : a. name b.
>> bought_price c. stock 3. One PushButton
>>
>> i have three slot: 1. responseToRequestForData()  2.setFilterDict()
>> 3.unSetFilterDict()
>> responseToRequestForData(): start to search in DB setFilterDict(): fill
>> a dict from my LineEdit
>>
>> Problem:
>> My name is filled in dict but its value doesn't fill up. b and c don't
>> have any problem.
> I'm afraid I don't understand this. Even your followup post doesn't
> really help:
>
>> I see same output in console:
>> {'stock': 2, 'name': PyQt4.QtCore.QString(u''), 'bought_price': 23}
>
> What result where you expecting?
>
> If I remember correctly, Qt strings are mutable unicode strings, so
> 'name' is associated with an empty Qt string. If they are mutable, that
> means that once the dict is set:
>
> {'name': QString(u'contents of text field'), ...}
>
>
> if the text field changes, so will the string. Is that what is happening?
>
> (Or perhaps I have mis-remembered about Qt strings.)
>
> You have two callbacks that appear to set the "name" key in the dict.
> Perhaps one of them is setting it to an empty value.
>
>
>
>

_fromUtf8 is needed for the API compatibility, at the beginning of the code of Moshen it is these lines:

try:
     _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
     _fromUtf8 = lambda s: s


Moshen, I thing if you pass the instance of your GUI at the class materialsInstance you'll can simplify your connections

self.lineEdit.returnPressed.connect(self.materialsInstance.responseToRequestForData)
self.lineEdit.editingFinnished.connect(self.materialsInstance.responseToRequestForData)

For the checkBoxes, I'm not sure you need all these arguments but I don't know enough your code.


-- 
Vincent V.V.
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