QtreeView: keep aspect ratio when resizing a column

resize_row_via_delegate.py

import sys
from PyQt5 import QtWidgets, QtGui, QtCore


def fetch_data():
    return [
        {
            'name': 'horizontal',
            'image': {
                'colour': (255, 0, 0),
                'width': 480,
                'height': 240,
            },
        },
        {
            'name': 'vertical',
            'image': {
                'colour': (0, 255, 0),
                'width': 240,
                'height': 480,
            },
        },
        {
            'name': 'none',
            'image': {},
        },
        {
            'name': 'square',
            'image': {
                'colour': (0, 0, 255),
                'width': 480,
                'height': 480,
            },
        },
    ]




class MyModel(QtCore.QAbstractItemModel):
    def __init__(self, raw_data, *args, **kwargs):
        super(MyModel, self).__init__(*args, **kwargs)
        self._raw_data = raw_data

    def index(self, row, column, parent):
        ptr = self._raw_data[row] if row < len(self._raw_data) else None
        return self.createIndex(row, column, ptr)

    def parent(self, index):
        return QtCore.QModelIndex()

    def hasChildren(self, index):
        return index.internalPointer() is None

    def rowCount(self, parent):
        return len(self._raw_data)

    def columnCount(self, parent):
        return 2  # preview, name

    def headerData(self, section, orientation, role):
        if role == QtCore.Qt.DisplayRole and orientation == QtCore.Qt.Horizontal:
            return ('Preview', 'Name')[section]

    def data(self, index, role):
        d = index.internalPointer()
        if role == QtCore.Qt.UserRole:
            return d
        column = index.column()
        if column == 0:
            if role == QtCore.Qt.DecorationRole:
                if not d['image']:
                    return
                p = QtGui.QPixmap(d['image']['width'], d['image']['height'])
                p.fill(QtGui.QColor(*d['image']['colour']))
                return p
        elif column == 1:
            if role == QtCore.Qt.DisplayRole:
                return d['name']



class MyDelegate(QtWidgets.QStyledItemDelegate):

    def sizeHint(self, option, index):
        if not hasattr(self, '_static_hints'):
            self._static_hints = {}
        size = super(MyDelegate, self).sizeHint(option, index)
        d = index.data(QtCore.Qt.UserRole)
        if index.column() == 0 and d['image']:
            ratio = d['image']['height']/float(d['image']['width'])
            width = option.widget.columnWidth(index.column())
            size = QtCore.QSize(width, width * ratio)

        # sizeHint gets called when the model's data changes, therefore even
        # tho we compute the image size correctly it doesn't get called when
        # the user resize a column (notice this is an action on the view and
        # doesn't change nothing in the viewport)
        # we are going to store the last computed size hints in a dictionary
        # so we have a way to check if an update is necesary while painting
        if not hasattr(self, '_static_hints'):
            self._static_hints = {}
        self._static_hints[index] = size
        return size

    def paint(self, painter, option, index):
        d = index.data(QtCore.Qt.UserRole)
        if index.column() == 0 and d['image']:
            ratio = d['image']['height']/float(d['image']['width'])
            width = option.widget.columnWidth(index.column())
            rect = QtCore.QRect(0, option.rect.y(),
                                width, (width * ratio))
            painter.drawPixmap(rect, index.data(QtCore.Qt.DecorationRole))

            if self._static_hints[index].height() != rect.height():
                # update row height update by emitting dataChanged signal (in the model)
                # which will force the view to recompute the sizeHint
                model = option.widget.model()
                model.dataChanged.emit(index, index, [QtCore.Qt.DecorationRole])
            return
        return super(MyDelegate, self).paint(painter, option, index)



if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    mw = QtWidgets.QMainWindow()

    model = MyModel(fetch_data())
    delegate = MyDelegate()
    tree = QtWidgets.QTreeView()
    tree.setItemDelegate(delegate)
    tree.setModel(model)
    
    mw.setCentralWidget(tree)
    mw.show()
    sys.exit(app.exec_())