def sizeHint(self):
        size = QtCore.QSize()
        for name in self._editor.names:
            size = size.expandedTo(self._editor.get_pixmap(name).size())

        option = QtGui.QStyleOptionComboBox()
        self.initStyleOption(option)
        size = self.style().sizeFromContents(QtGui.QStyle.CT_ComboBox, option,
                                             size, self)
        return size
Reimplemented to set a size hint based on the size of the larget
dataset/ETHPy150Open enthought/traitsui/traitsui/qt4/image_enum_editor.py/ImageEnumComboBox.sizeHint