PyQt5 - Adding widget to layout dynamically

Question

I'm trying to create a custom widget where the user can dynamically add more [some other] custom widget onto the window. Here is my attempt:

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtCore import Qt


class LoadModelWidget(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super(LoadModelWidget, self).__init__(*args, **kwargs)

        # ------------------------ GUI Components ------------------------ #
        self.setFixedHeight(100)
        self._container = QtWidgets.QGroupBox(self)
        self._container.setSizePolicy(QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Expanding))
        self._container.setFixedHeight(100)
        self._container.setFixedWidth(210)
        layout = QtWidgets.QGridLayout()

        self._model_to_select_label = QtWidgets.QLabel("Selected model")
        layout.addWidget(self._model_to_select_label, 0, 0)
        self._model_to_select_list = QtWidgets.QComboBox()
        layout.addWidget(self._model_to_select_list, 0, 1)
        _slice_method_label = QtWidgets.QLabel("Slice method")
        layout.addWidget(_slice_method_label, 1, 0)
        self._list_of_slicing_method = QtWidgets.QComboBox()
        layout.addWidget(self._list_of_slicing_method, 1, 1)

        self._bottom_radius_label = QtWidgets.QLabel("Bottom radius")
        layout.addWidget(self._bottom_radius_label, 2, 0)
        self._bottom_radius_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._bottom_radius_edit, 2, 1)
        self._top_radius_label = QtWidgets.QLabel("Top radius")
        layout.addWidget(self._top_radius_label, 3, 0)
        self._top_radius_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._top_radius_edit, 3, 1)
        self._height_label = QtWidgets.QLabel("Height")
        layout.addWidget(self._height_label, 4, 0)
        self._height_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._height_edit, 4, 1)

        self._x_dir_label = QtWidgets.QLabel("X direction")
        layout.addWidget(self._x_dir_label, 5, 0)
        self._x_dir_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._x_dir_edit, 5, 1)
        self._y_dir_label = QtWidgets.QLabel("Y direction")
        layout.addWidget(self._y_dir_label, 6, 0)
        self._y_dir_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._y_dir_edit, 6, 1)
        self._z_dir_label = QtWidgets.QLabel("Z direction")
        layout.addWidget(self._z_dir_label, 7, 0)
        self._z_dir_edit = QtWidgets.QLineEdit()
        layout.addWidget(self._z_dir_edit, 7, 1)

        self._remove_btn = QtWidgets.QPushButton("Remove model")
        layout.addWidget(self._remove_btn, 8, 0)

        self._bottom_radius_label.setVisible(False)
        self._bottom_radius_edit.setVisible(False)
        self._top_radius_label.setVisible(False)
        self._top_radius_edit.setVisible(False)
        self._height_label.setVisible(False)
        self._height_edit.setVisible(False)
        self._x_dir_label.setVisible(False)
        self._x_dir_edit.setVisible(False)
        self._y_dir_label.setVisible(False)
        self._y_dir_edit.setVisible(False)
        self._z_dir_label.setVisible(False)
        self._z_dir_edit.setVisible(False)

        self._container.setLayout(layout)

        # -------------------- Other attributes -------------------- "
        self._filename = ""

        # -------------------- Assign slot and signal -------------------- "
        self._list_of_slicing_method.currentIndexChanged.connect(self.slice_method_changed)
        self._remove_btn.clicked.connect(self.remove_model)

    def set_model_dir(self, filename, filedir, suggested_slicing_method="Parallel"):
        # Assign only the name of the file, not the whole stl model
        self._filename = filename
        self._filedir = filedir

        self._list_of_slicing_method.addItem("Parallel")
        self._list_of_slicing_method.addItem("Revolution")
        self._list_of_slicing_method.addItem("Radial")
        self._list_of_slicing_method.addItem("ParallelCurve")

        self._list_of_slicing_method.setCurrentText(suggested_slicing_method)

    def get_model_full_dir(self):
        return self._filedir + "\\" + self._filename

    def remove_model(self):
        self._filename = ""
        self._filedir = ""
        self._list_of_slicing_method.clear()

    def slice_method_changed(self):
        is_parallel = self._list_of_slicing_method.currentText() == "Parallel"
        is_radial = self._list_of_slicing_method.currentText() == "Radial"

        self._bottom_radius_label.setVisible(is_radial)
        self._bottom_radius_edit.setVisible(is_radial)
        self._top_radius_label.setVisible(is_radial)
        self._top_radius_edit.setVisible(is_radial)
        self._height_label.setVisible(is_radial)
        self._height_edit.setVisible(is_radial)

        self._x_dir_label.setVisible(is_parallel)
        self._x_dir_edit.setVisible(is_parallel)
        self._y_dir_label.setVisible(is_parallel)
        self._y_dir_edit.setVisible(is_parallel)
        self._z_dir_label.setVisible(is_parallel)
        self._z_dir_edit.setVisible(is_parallel)

        padding = 50
        minimum_height = 100
        new_height = (self._bottom_radius_label.height() + padding)*is_radial + (self._top_radius_edit.height() + padding)*is_radial + (self._height_label.height() + padding)*is_radial + (self._x_dir_label.height() + padding)*is_parallel + (self._y_dir_label.height() + padding)*is_parallel + (self._z_dir_label.height() + padding)*is_parallel
        if (new_height > minimum_height):
            self._container.setFixedHeight(new_height)
            self.setFixedHeight(new_height)
        else:
            self._container.setFixedHeight(minimum_height)
            self.setFixedHeight(minimum_height)

class LoadModelColumn(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super(LoadModelColumn, self).__init__(*args, **kwargs)

        # ------------------------ GUI Components ------------------------ #
        self._layout = QtWidgets.QGridLayout()
        self._add_model_btn = QtWidgets.QPushButton("Add model(s)")
        self._layout.addWidget(self._add_model_btn, 0, 0)
        self._clear_all_btn = QtWidgets.QPushButton("Clear all")
        self._layout.addWidget(self._clear_all_btn, 0, 1)

        self._all_load_model_widgets = []

        self.verticalSpacer = QtWidgets.QSpacerItem(20, 40, QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.MinimumExpanding)
        self._layout.addItem(self.verticalSpacer)

        self._load_model_group = QtWidgets.QGroupBox()
        self._load_model_group.setLayout(self._layout)

        self._scroll_area = QtWidgets.QScrollArea(self)
        self._scroll_area.setWidgetResizable(True)
        self._scroll_area.setFixedHeight(600)
        self._scroll_area.setFixedWidth(250)
        self._scroll_area.setVerticalScrollBarPolicy(Qt.ScrollBarAlwaysOn)
        self._scroll_area.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
        self._scroll_area.setWidget(self._load_model_group)

        # -------------------- Assign slot and signal -------------------- "
        self._clear_all_btn.clicked.connect(self._clear_all_models)
        self._add_model_btn.clicked.connect(self._add_models)

    def _clear_all_models(self):
        for widget in self._all_load_model_widgets:
            self._layout.removeWidget(widget)
            widget.deleteLater()

        self._all_load_model_widgets = []

    def _add_models(self):
        widget = LoadModelWidget()
        widget.set_model_dir("hi", "hello")
        self._all_load_model_widgets.append(widget)
        self._layout.addWidget(widget, len(self._all_load_model_widgets), 0, 1, 0)

Currently, when a widget is added, for some reason, it will try to occupy all the scroll area. But obviously, I don't really want that since I would like it to be allocated to the necessary space only.

Here's an example of what it is doing right now when the user press Add Model(s) button:

But this is what I would like it to be:

Answer 1

You are adding widgets to a top level window widget, but you're not setting a layout for them.

The simple answer for your issue is to correctly set the layout for the widgets you're creating. Add the following at the bottom of LoadModelWidget 's __init__ :

        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(self._container)

and this at the bottom the __init__ of LoadModelColumn :

        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(self._scroll_area)

Then remove all unnecessary setFixedHeight , which don't make any sense.

I strongly suggest you to better study how layout manager work , since all widgets that require adjusting their contents also require that you set a layout for them.
Then I also suggest you to better clarify the object structure of your classes. For example, there's no need to subclass LoadModelWidget from QWidget, if it will always contain a single group box: just subclass QGroupBox.

_{As a side note (but, still, very important), always try to keep your examples as minimal as possible (read more about creating minimal, reproducible examples (you might even end up finding the solution on your own); also, and that's also very important, always make efforts to make those examples immediately reproducible : from your code, it was not clear what class was used as the parent), and your example is very long; we must be able to copy and paste your code and run it with as little efforts as possible: this means that we want to help you, but you have to help us to help you.}