Why the central widget(QWidget) doesn't get sized properly when its imported from another file?

Question

when i tried to split the code in another file to be more manageable a undesirable behavior took place. My Qwidget when imported from another file gets small on the screen. if we were to replace the line to set CentralWidget from:

self.setCentralWidget(self.view)

to:

self.setCentralWidget(QTextEdit())

the textedit widget would show with no problems, fully sized. Is that a QgraphicsView Problem or layout problem i am dealing with?

Part relevant of code in main.py

import sys
from PySide2.QtCore import *
from PySide2.QtGui import *
from PySide2.QtWidgets import *
from viewport import ViewPort

class dockdemo(QMainWindow):
    def __init__(self, parent=None):
        super(dockdemo, self).__init__(parent)
        self.view:QWidget = ViewPort()

    bar = self.menuBar()
    file = bar.addMenu("File")
    file.addAction("New")
    file.addAction("save")
    file.addAction("quit")

    # buttons layout
    buttons = QWidget()
    vert_layout = QVBoxLayout()
    button = QPushButton("Rotate - ", self)
    button.setGeometry(200, 450, 100, 50)
    button.clicked.connect(self.view.rotate_minus)
    button2 = QPushButton("Rotate + ", self)
    button2.setGeometry(320, 450, 100, 50)
    button2.clicked.connect(self.view.rotate_plus)
    button3 = QPushButton("zoom-in ", self)
    button3.clicked.connect(self.view.zoom_in)
    button4 = QPushButton("zoom-out ", self)
    button4.clicked.connect(self.view.zoom_out)
    button5 = QPushButton("reset zoom ", self)
    button5.clicked.connect(self.view.reset_zoom)
    vert_layout.addWidget(button)
    vert_layout.addWidget(button2)
    vert_layout.addWidget(button3)
    vert_layout.addWidget(button4)
    vert_layout.addWidget(button5)
    buttons.setLayout(vert_layout)

    self.Mydock = QDockWidget("Dockable", self)
    self.Mydock.setWidget(buttons)
    self.Mydock.setFloating(False)

    self.addDockWidget(Qt.LeftDockWidgetArea, self.Mydock)

    self.setCentralWidget(self.view)

    self.setWindowTitle("Dock demo")

my qwidget in viewport.py

import sys
from PySide2.QtCore import *
from PySide2.QtGui import *
from PySide2.QtWidgets import *
class ViewPort(QWidget):
    def __init__(self, parent=None):
        super(ViewPort, self).__init__(parent)

    self.scene = QGraphicsScene(self)
    greenBrush = QBrush(Qt.green)
    blueBrush = QBrush(Qt.blue)

    blackPen = QPen(Qt.black)
    blackPen.setWidth(5)

    ellipse = self.scene.addEllipse(10, 10, 11, 11, blackPen, greenBrush)
    ellipse.moveBy(100, 0)
    rect = self.scene.addRect(-100, -100, 200, 200, blackPen, blueBrush)

    self.scene.addText("Codeloop.org", QFont("Sanserif", 15))

    ellipse.setFlag(QGraphicsItem.ItemIsMovable)
    rect.setFlag(QGraphicsItem.ItemIsMovable)

    self.view = QGraphicsView(self.scene, self)
    setattr(self.view, 'scale_of_viewport', 0)

    # filter event so mouse wheel wont scroll. see def event filter
    self.view.viewport().installEventFilter(self)

result:

expected result (which happens if i implement the Qgraphicsview from main.py):

so because i wanted to implement the viewport on a diferent file (viewport.py) the widget doesn't take over the screen anymore like it was supposed to. i've tried setGeometry(), setminimumsize(), and changeging layouts without any success. i just wanna be able to implement the qwidgets in different files before they get gigantic. I couldn't find the answer online. Thanks for any help.

Answer 1

Problem

As you guessed, is a problem with the layout. Your ViewpPort Widget doesn't have an organized structure. That means the size of the QGraphicsView (inside ViewPort) doesn´t have any relation with the size of the ViewPort widget. And when you try to adjust the size of ViewPort inside dockdemo, the QGraphicsView won't be affected.

Solution

Just add a layout inside your ViewPort widget, and then add the QGraphicsView inside it. Here is your ViewPort class changed (With the changes commented):

    class ViewPort(QWidget):
        def __init__(self, parent=None):
            super(ViewPort, self).__init__(parent)
            ## Create a Layout and set it in the widget, 
            ## in this case I created a Vertical Layout
            central_layout = QVBoxLayout()
            self.setLayout(central_layout)
            ## (end)
            self.scene = QGraphicsScene(self)
            greenBrush = QBrush(Qt.green)
            blueBrush = QBrush(Qt.blue)
            blackPen = QPen(Qt.black)
            blackPen.setWidth(5)
            ellipse = self.scene.addEllipse(10, 10, 11, 11, blackPen, greenBrush)
            ellipse.moveBy(100, 0)
            rect = self.scene.addRect(-100, -100, 200, 200, blackPen, blueBrush)
            self.scene.addText("Codeloop.org", QFont("Sanserif", 15))
            ellipse.setFlag(QGraphicsItem.ItemIsMovable)
            rect.setFlag(QGraphicsItem.ItemIsMovable)
            self.view = QGraphicsView(self.scene, self)
            setattr(self.view, 'scale_of_viewport', 0)
            self.view.viewport().installEventFilter(self)
            ## Add your QGraphicsView inside the layout
            central_layout.addWidget(self.view)
            ## (end)

And here is the result:

(I used PyQt5, but I think this works fine in PySide2, tell if it works)