How to modify this PyQt5 current setup to enable drag resize between layouts

Question

How to modify this current setup to enable resizing(horizontally and vertically) between the layouts shown below? Let\'s say I want to resize the lists in the right toward the l

Answer 1

One way to rescale the image to an arbitrary size while maintaining its aspect ratio is to subclass QWidget and override sizeHint and paintEvent and use that instead of a QLabel for displaying the image, e.g.

class PixmapWidget(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding)
        self._pixmap = None

    def sizeHint(self):
        if self._pixmap:
            return self._pixmap.size()
        else:
            return QSize()

    def setPixmap(self, pixmap):
        self._pixmap = pixmap
        self.update()

    def paintEvent(self, event):
        painter = QPainter(self)
        super().paintEvent(event)
        if self._pixmap:
            size = self._pixmap.size().scaled(self.size(), Qt.KeepAspectRatio)
            offset = (self.size() - size)/2
            rect = QRect(offset.width(), offset.height(), size.width(), size.height())
            painter.drawPixmap(rect, self._pixmap)

Since you are subclassing QMainWindow you could use DockWidgets to display the lists instead of adding them to the layout of the central widget, e.g.

class TestWindow(QMainWindow):
    def __init__(self, left_ratio, right_ratio, window_title):
        super().__init__()
        #self.left_ratio = left_ratio    <--- not needed since image and lists
        #self.right_ratio = right_ratio  <--- are not sharing a layout anymore

        ...

        # use PixmapWidget instead of QLabel for showing image
        # refactor dictionary for storing lists to make adding DockWidgets easier
        self.left_widgets = {'Image': PixmapWidget()}
        self.right_widgets = {'List1': QListWidget(),
                              'List2': QListWidget()}
        self.central_widget = QWidget(self)
        # self.main_layout = QHBoxLayout()  <-- not needed anymore
        self.left_layout = QVBoxLayout()

        self.adjust_widgets()
        self.adjust_layouts()
        self.show()

    def adjust_layouts(self):
        self.central_widget.setLayout(self.left_layout)
        self.setCentralWidget(self.central_widget)

    def adjust_widgets(self):
        self.left_layout.addWidget(self.left_widgets['Image'])
        self.left_widgets['Image'].setPixmap(QPixmap('test.jpg').scaled(500, 400, Qt.IgnoreAspectRatio, Qt.SmoothTransformation))

        self.dock_widgets = []
        for text, widget in self.right_widgets.items():
            dock_widget = QDockWidget(text)
            dock_widget.setFeatures(QDockWidget.NoDockWidgetFeatures)
            dock_widget.setWidget(widget)
            self.addDockWidget(Qt.RightDockWidgetArea, dock_widget)
            self.dock_widgets.append(dock_widget)

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