[FIXED] QTreeView not spanning parent width or height

Issue

So I am new to QtGui and looking up how to do things, and I found this neat example on QTreeView. When I got it working on my own, I noticed that it didn't fill the space as I'd anticipated:

So I have been searching for answers, and not finding much in either Python or C++ resources. I've been checking the documentation a lot, but still not quite finding what I'm searching for.

So it seems clear that something doesn't have the correct size policy, but I am having a hard time figuring out what. I have so far eliminated a couple of potential candidates:

• The QWidget instance holding the QTreeView instance is correctly spanning the layout it is in (the QWidget spans the width of the QGroupBox minus a little for margins).
• Since QTreeView's parent widget is the correct dimensions, I figured it's something more local to QTreeView, but when I use the setSizePolicy, none of the policies I've used seem to resolve the issue. Possibly multiple steps I'm unaware of?
• The QTreeView's inherited viewport (from QAbstractScrollArea is much smaller than I expect. Calling QTreeView's setViewport() method with a new and empty QWidget only redraws the non-header contents background in gray instead of white, and I suspect that this is close but not where I need to look.
• QTreeView has other children (besides viewport)that I am still investigating.
• Most of what I have tried I left commented out in my code below.

This is my source code to reproduce:

import sys
from PySide.QtGui import *


class TreeTime(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.main_widget = QWidget()
        self.main_layout = QVBoxLayout()
        self.main_widget.setLayout(self.main_layout)
        self.setCentralWidget(self.main_widget)
        self.statusBar()

        self.make_tree()

        self.show()

    def make_tree(self):
        # init widgets
        self.tgb = QGroupBox("[Tree Group Box Title]")
        self.main_layout.addWidget(self.tgb)

        tgb_layout = QVBoxLayout()
        self.tgb.setLayout(tgb_layout)

        tgb_widget = QWidget()
        tgb_layout.addWidget(tgb_widget)

        debug_btn = QPushButton("DEBUG")
        tgb_layout.addWidget(debug_btn)

        view = QTreeView(parent=tgb_widget)
        # view.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
        view.setSelectionBehavior(QAbstractItemView.SelectRows)
        model = QStandardItemModel()
        model.setHorizontalHeaderLabels(['col1', 'col2', 'col3'])
        view.setModel(model)
        view.setUniformRowHeights(True)

        # populate data
        for i in range(10):
            parent1 = QStandardItem('Family {}. Some long status text for sp'.format(i))
            for j in range(3):
                child1 = QStandardItem('Child {}'.format(i*3+j))
                child2 = QStandardItem('row: {}, col: {}'.format(i, j+1))
                child3 = QStandardItem('row: {}, col: {}'.format(i, j+2))
                parent1.appendRow([child1, child2, child3])
            model.appendRow(parent1)
            # span container columns
            view.setFirstColumnSpanned(i, view.rootIndex(), True)

        # expand third container
        index = model.indexFromItem(parent1)
        view.expand(index)

        # select last row
        selmod = view.selectionModel()
        index2 = model.indexFromItem(child3)
        selmod.select(index2, QItemSelectionModel.Select|QItemSelectionModel.Rows)

        def print_debug_info():
            print('')
            for child in view.children():
                print("child "+repr(child)) #not sure what all these are yet
            print('')
            print('self.main_widget.frameSize: '+repr(self.main_widget.frameSize()))
            print('view.parent().parent().frameSize(): '+repr(view.parent().parent().frameSize())) #group box
            # print('self.frameSize: '+repr(self.frameSize()))
            print('self.tgb.frameSize: '+repr(self.tgb.frameSize()))
            print('view.parent(): '+repr(view.parent()))
            print('view.parent().frameSize(): '+repr(view.parent().frameSize()))
            # print('view.parent().frameSize(): '+repr(view.parent().frameSize())+" (before)")
            # print('view.parent().adjustSize(): '+repr(view.parent().adjustSize()))
            # print('view.parent().frameSize(): '+repr(view.parent().frameSize())+" (after)")
            print('view.viewport(): '+repr(view.viewport()))
            print('view.viewport().frameSize(): '+repr(view.viewport().frameSize()))
            # print('view.parent().parent().parent().frameSize(): '+repr(view.parent().parent().parent().frameSize()))
            # print('calling setViewport: '+repr(view.setViewport(QWidget())))
            # view.adjustSize()

        debug_btn.clicked.connect(print_debug_info)

    def sayHello(self):
        self.statusBar().showMessage("Hello World!")
        import time; time.sleep(2)
        self.statusBar().showMessage("")

    def sayWords(self, words):
        self.statusBar().showMessage(words)


if __name__ == '__main__':
    app = QApplication([])
    tt = TreeTime()
    sys.exit(app.exec_())

I am using a Windows 8.1 machine and Python 3.4.3, PySide version 1.2.2 - any help will be much appreciated! (also, please let me know if I left out any important details)

UPDATE (5/19/2015): I tried moving my DEBUG button outside the QGroupBox, and the result was the QTreeView being collapsed into a completely nonlegible size so you couldn't even tell what the object was anymore, so it seems to be minimizing the space used, even when I uncomment the line:

view.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)

One friend has suggested this may simply be an issue with windows and not my code, but I don't have anything to back that up.

UPDATE 5/19/2015: I have implemented the advice provided by @titusjan, but I have the same problem/behavior.

Solution

You need to remove the redundant tp_widget and add view to tgb_layout:

def make_tree(self):
    # init widgets
    self.tgb = QGroupBox("[Tree Group Box Title]")
    self.main_layout.addWidget(self.tgb)

    tgb_layout = QVBoxLayout()
    self.tgb.setLayout(tgb_layout)

    view = QTreeView()
    tgb_layout.addWidget(view)

    ...

    debug_btn = QPushButton("DEBUG")
    tgb_layout.addWidget(debug_btn)

Note that when you add widgets to a layout, they will be automatically re-parented to the parent of the layout (whenever it gets one), so it's not really necessary set one in the constructor.

Also note that this:

    tgb_layout = QVBoxLayout(self.tgb)

is exactly equivalent to this:

    tgb_layout = QVBoxLayout()
    self.tgb.setLayout(tgb_layout)

because the layout will always be re-parented to the widget it's set on.

Answered By - ekhumoro