On Tuesday, September 26, 2017 at 11:18:54 AM UTC+5:30, Veek M wrote:
> Summary: Could someone explain widget and dialog parenting - the text book is
> not making sense.
> ######################
> I'm trying to understand widget parenting, from the book: Rapid GUI
> Programming, pg 118, and thereabouts - he says:
>
> A. All PyQt classes that derive from QObjectand this includes all the widgets,
> since QWidget is a QObject subclasscan have a “parent”.
>
> B. PyQt automatically repar-
> ents the widgets that are laid out. So although we did not give our widgets a
> parent of self (the Form instance),when we call setLayout() the layout manager
> gives ownership of the widgets and of itself to the form,and takes ownership
> of
> any nested layouts itself. This means that none of the widgets that are laid
> out
> is a top-level window, and all of them have parents, which is what we want. So
> when the form is deleted, all its child widgets and layouts will be deleted
> with
> -----------------------------
> 1. In A, does he mean, you are ALLOWED to set a parent on a widget ONLY
> because its Base Class is QObject?
>
> With DockWidgets, you have to explicitly parent them - why?
>
> 2. If I create two widgets and wdget.show() them, and app.exec_() - which one
> becomes the main-window and which one is the memory leak? I have not used a
> layout manager so, one widget with no parent auto-becomes the main-window (as
> per B), which would result in a leak with the other?
>
> #!/usr/bin/python
>
> import sys, os, re
>
>
> from PyQt4.QtCore import *
> from PyQt4.QtGui import *
>
> app = QApplication(sys.argv)
>
> lbl = QLabel('<font size=11 color=red><b>Hello World</b></font>')
> lbl.setWindowFlags(Qt.SplashScreen)
> lbl.show()
> txtBrw = QTextBrowser()
> txtBrw.show()
>
> QTimer.singleShot(3000, app.quit)
> app.exec_()
>
> 3. QObject --> QWidget --> QDialog --> Form --> Form_Layout_Manager -->
> Nested_Layout_Manager
>
> B, says that the layout manager parents the widgets under it and makes 'Form'
> the parent. If the Form Layout Manager is taking charge of the Nested Layout
> Manager, who is the parent of the widgets under the Nested Layout Mangaer?
>
> 4. In the Chapter on 'Dialogs', I am trying to create a QMainWindow Style
> application with one label as the central widget and one button to invoke a
> dialog. It doesn't work and I get:
>
> QWidget::setLayout: Attempting to set QLayout "" on Parent "", which already
> has a layout
>
> I tried this link and it made no sense:
> https://stackoverflow.com/questions/25450598/qlayout-attempting-to-add-qlayout-to-qwidget-which-already-has-a-layout
>
> How does parenting work in PyQt? What is autoparented, what needs to be
> explicitly parented and who is scrwing whom? Additionally, why is my button,
> hiding?
>
>
> #!/usr/bin/python
>
> import sys, os, re
>
>
> from PyQt4.QtCore import *
> from PyQt4.QtGui import *
>
> app = QApplication(sys.argv)
>
> class Dialog(QDialog):
> def __init__(self, parent = None):
> super(Dialog, self).__init__(parent)
>
> self.lbl = QLabel('Width: ')
> self.spn = QSpinBox()
> self.spn.setRange(0, 100)
> self.lbl.setBuddy(self.spn)
>
> self.chk = QCheckBox('&Beveled Edges')
>
> self.lbl_styl = QLabel('Style')
> self.lst = QComboBox()
> self.lst.addItems(['dashed', 'dotted', 'star'])
> self.lbl_styl.setBuddy(self.lst)
>
> self.ok_btn = QPushButton('&Ok')
> self.cncl_btn = QPushButton('&Cancel')
>
> self.layout([(self.lbl, 0, 0), (self.spn, 0, 1), (self.chk, 0, 2),
> (self.lbl_styl, 1, 0), (self.lst, 1, 1),
> (self.ok_btn, 2, 0), (self.cncl_btn, 2, 1)])
>
> def layout(self, wgts = []):
> self.lyt = QGridLayout()
> for wgt, row, col in wgts:
> self.lyt.addWidget(wgt, row, col)
>
> self.setLayout(self.lyt)
>
>
> class Parent(QMainWindow):
> def __init__(self, parent = None):
> super(Parent, self).__init__(parent)
>
> lbl = QLabel('HELLO WORLD')
> btn = QPushButton('&Start Dialog')
> lbl.setBuddy(btn)
>
> lyt = QHBoxLayout()
> lyt.addWidget(lbl)
> lyt.addWidget(btn)
>
> self.setLayout(lyt)
> self.connect(btn, SIGNAL('clicked()'), self.popup_dialog)
>
> def popup_dialog(self):
> x = Dialog(self)
> if x.exec_():
> print(x.spn.value())
>
> p = Parent()
> p.show()
>
> app.exec_()
I fixed some of it by deleting the:
Parent
self.setLayout(lyt)
I don't understand why that works - aren't we supposed to attach a layout to
the Parent/MainWindow object? Why not?
Also, I made the:
Parent
self.setCentralWidget(btn)
so the button is the central widget. To use the Label, I think I would have to
create a composite widget which is too complicated for me, currently.
Now. it works so I tested some more and added:
def popup_dialog(self):
x = Dialog(self)
y = Dialog(self)
y.show()
if x.exec_():
print(x.spn.value())
AND
class Dialog(QDialog):
self.connect(self.cncl_btn, SIGNAL('clicked()'), self.close)
So my dialog pops up and because exec_ is being called on 'x', I have to first
close that widget before I can interact with my button and 'y'. However, let's
say I close the 'x' dialog - then I can click on 'Button' and I get two more
dialogs which don't lock anything - why??
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