QStyledItemDelegate's Option Is Not Updating

I ran into a problem while using PyQt5. I have a list with QStyledItemDelegate class painting its items. Here is the minimal reproducible example: import sys from PyQt5.QtCore impo

Solution 1:

When the size hint of an index changes, you need to emit MessageDelegate.sizeHintChanged to let the layout manager of the items know that it needs to redistribute the items. In this case the height of the items only changes when the window is resized, so what you could do is to emit a (custom) signal in Dialog.resizeEvent and connect it to MessageDelegate.sizeHintChanged. For this Dialog would need to be modified according to something like this

from PyQt5.QtCore import pyqtSignal, QModelIndex

class Dialog(QMainWindow):

    # custom signal for signalling when window is resized
    width_changed = pyqtSignal()

    def __init__(self):
        ... as before ...
        self.messages = QListView()
        delegate = MessageDelegate()
        self.messages.setItemDelegate(delegate)
        # Connect custom signal to delegate.sizeHintChanged. 
        # This signal expects a ModelIndex for which we take the root, i.e. QModelIndex()  
        self.width_changed.connect(lambda : delegate.sizeHintChanged.emit(QModelIndex()))
        .... rest as before ....

    def resizeEvent(self, event):
        global window_width
        super(Dialog, self).resizeEvent(event)
        window_width = self.size().width()
        # emit the custom signal
        self.width_changed.emit()

In the code above I didn't modify anything else in the code, but you could opt to get rid of the global window_width variable by modifying the custom signal to emit the new width and create a slot in MessageDelegate to assign the new width to an instance variable.

Solution 2:

Wrapping of item contents is already implemented inside QListView and can be enabled with self.messages.setWordWrap(True). If you use delegate only for text wrapping you dont need it at all.