QStyledItemDelegate.sizeHint() works only if my TableModel has rows

[AlexVhr]

Hi! I've a usual TableView-TableModel-Delegate setup, and use Delegate.sizeHint() to control column width. It works perfectly, but only when my model has rows. If it's empty, then columns have default width, which is not good. What can be the couse of it? Full test case follows (python):

import sys
from PySide import QtGui, QtCore
 
class Person:
    def __init__(self, f_name, l_name, country):
        self.f_name = f_name
        self.l_name = l_name
        self.country = country
 
class MyDelegate(QtGui.QStyledItemDelegate):
    def sizeHint(self, option, index):
        super().sizeHint(option, index)
        width = index.model().sizes[index.column()]
        return QtCore.QSize(width, 24)
 
class MyModel(QtCore.QAbstractTableModel):
 
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.columns = ['f_name','l_name', 'country']
        self.sizes = [70, 70, 35]
        self.rows = [Person('John', 'Doe', 'USA'),
                      Person('Hans', 'Mann', 'DE')]
        #self.rows = [] #uncomment this to see it fail
 
    def rowCount(self, *args, **kwargs):
        return len(self.rows)
 
    def columnCount(self, *args, **kwargs):
        return len(self.columns)
 
    def data(self, index, role):
        if index.isValid():
            if role == QtCore.Qt.DisplayRole:
                row = self.rows[index.row()]
                col = self.columns[index.column()]
                attr = getattr(row, col)
                return attr
 
if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    win = QtGui.QTableView()
    win.setModel(MyModel())
    win.setItemDelegate(MyDelegate(win))
    win.resizeColumnsToContents()
    win.show()
    sys.exit(app.exec_())

import sys
from PySide import QtGui, QtCore

class Person:
    def __init__(self, f_name, l_name, country):
        self.f_name = f_name
        self.l_name = l_name
        self.country = country

class MyDelegate(QtGui.QStyledItemDelegate):
    def sizeHint(self, option, index):
        super().sizeHint(option, index)
        width = index.model().sizes[index.column()]
        return QtCore.QSize(width, 24)

class MyModel(QtCore.QAbstractTableModel):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.columns = ['f_name','l_name', 'country']
        self.sizes = [70, 70, 35]
        self.rows = [Person('John', 'Doe', 'USA'),
                      Person('Hans', 'Mann', 'DE')]
        #self.rows = [] #uncomment this to see it fail

    def rowCount(self, *args, **kwargs):
        return len(self.rows)

    def columnCount(self, *args, **kwargs):
        return len(self.columns)

    def data(self, index, role):
        if index.isValid():
            if role == QtCore.Qt.DisplayRole:
                row = self.rows[index.row()]
                col = self.columns[index.column()]
                attr = getattr(row, col)
                return attr

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    win = QtGui.QTableView()
    win.setModel(MyModel())
    win.setItemDelegate(MyDelegate(win))
    win.resizeColumnsToContents()
    win.show()
    sys.exit(app.exec_())

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[wysota]

sizeHint() needs a valid index. If you don't have rows in your table, what are you calling sizeHint() on?

[AlexVhr]

Sounds logical, thanks. So I guess setting column width within delegates is a wrong approach in my case.

[wysota]

It depends what you want to do. If you program your delegate to return some size for an invalid index and you make sure the view calls your delegate when it has no rows to show, then you can do that.

[AlexVhr]

I want nothing fancy - just need to set column width from outside the model. Delegate seemed to be a logical choice. So about that "make sure the view calls your delegate when it has no rows to show" bit - how whould I go about that? Can I realy influence when and how the view invokes the delegate?

[wysota]

I want nothing fancy - just need to set column width from outside the model. Delegate seemed to be a logical choice.

You can set the column size by accessing the header object directly (QHeaderView::setDefaultSectionSize()).