pythonpyqtpyqt5qtreeviewqabstractitemmodel
how to show the proper number of columns in a QTreeView for a model with different hierarchical column counts
In the code example below I populate an item model with a set of top level items which contain key-value properties that I can view and edit with a QTreeView.
Looking at the Qt Documentation for QAbstractItemModel::columnCount it says that this should return the number of columns for the children of the given parent, meaning that this should be a hierarchical dependent property.
However, using the code below, if I return the column count as a hierarchical dependent property (in this case root->children have 1 column, root->child->children have 2 columns) then the view will only display 1 column.
Printing node.columnCount() (see the code) will actually show that the Item class nodes do in fact return columnCount = 2 after you expand one of the items.
If I just always return 2 for the model.columnCount function, then the view will properly display both columns.
Is this required to always return the desired number of columns in a view no matter the hierarchy or am I just doing something wrong and if so what? Returning a number of columns for a parent whose children have a different number of columns just to make the view work properly feels like it must be wrong.
import sys
import typing
from PyQt5 import QtCore, QtWidgets
class Node:
def __init__(self, parent=None):
self.parent = parent # type: Node
self.name : str
def children(self) -> list:
return None
def hasChildren(self):
return bool(self.children())
def getData(self, index: QtCore.QModelIndex):
if index.column() == 0:
return self.name
def setData(self, val, index: QtCore.QModelIndex):
if index.column() == 0:
self.name = val
def columnCount(self):
return 1
def rowCount(self):
children = self.children()
return 0 if not children else len(children)
def flags(self, index: QtCore.QModelIndex):
if index.column() == 0:
return (QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEditable)
else:
return QtCore.Qt.NoItemFlags
class Property(Node):
def __init__(self, parent, label, value):
super().__init__(parent)
self.label = label
self.value = value
def getData(self, index: QtCore.QModelIndex):
col = index.column()
if col == 0:
return self.label
elif col == 1:
return self.value
def setData(self, val, index: QtCore.QModelIndex):
if index.column() == 1:
self.value = val
def flags(self, index: QtCore.QModelIndex):
col = index.column()
if col == 0:
return QtCore.Qt.ItemIsEnabled
elif col == 1:
return QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsEditable | QtCore.Qt.ItemIsEditable
class Item(Node):
def __init__(self, parent):
super().__init__(parent)
self.name = 'Item'
self.p1 = Property(self, 'string', 'text')
self.p2 = Property(self, 'float', 1.2)
def children(self):
return [self.p1, self.p2]
def columnCount(self):
return 2
class Root(Node):
def __init__(self):
super().__init__(parent=None)
self._children = list()
def children(self):
return self._children
class Model(QtCore.QAbstractItemModel):
def __init__(self):
super().__init__()
self.root = Root()
def index(self, row: int, column: int, parent: QtCore.QModelIndex = ...) -> QtCore.QModelIndex:
if not self.hasIndex(row, column, parent):
return QtCore.QModelIndex()
node = parent.internalPointer() if parent.isValid() else self.root
if node.children:
return self.createIndex(row, column, node.children()[row])
else:
return QtCore.QModelIndex()
def parent(self, child: QtCore.QModelIndex) -> QtCore.QModelIndex:
if not child.isValid():
return QtCore.QModelIndex()
node = child.internalPointer() # type: Node
if node.parent and node.parent.parent:
row = node.parent.parent.children().index(node.parent)
return self.createIndex(row, 0, node.parent)
else:
return QtCore.QModelIndex()
def rowCount(self, parent: QtCore.QModelIndex = ...) -> int:
node = parent.internalPointer() if parent.isValid() else self.root
children = node.children()
return len(children) if children else 0
def columnCount(self, parent: QtCore.QModelIndex = ...) -> int:
node = parent.internalPointer() if parent.isValid() else self.root
print(f'{node.__class__.__name__} column count: ', node.columnCount()) # shows that column count 2 is returned, when items are expanded
# return 2 # 2nd column only shows up if I just always return 2
return node.columnCount() # view only shows 1 columns
def hasChildren(self, parent: QtCore.QModelIndex = ...) -> bool:
node = parent.internalPointer() if parent.isValid() else self.root
return node.hasChildren()
def data(self, index: QtCore.QModelIndex, role: int = ...):
if index.isValid() and role in (QtCore.Qt.DisplayRole, QtCore.Qt.EditRole):
node = index.internalPointer() # type: Node
return node.getData(index)
else:
return None
def setData(self, index: QtCore.QModelIndex, value: typing.Any, role: int = ...) -> bool:
if role in (QtCore.Qt.EditRole,):
node = index.internalPointer() # type: Node
node.setData(value, index)
self.dataChanged.emit(index, index)
return True
else:
return False
def flags(self, index: QtCore.QModelIndex):
node = index.internalPointer() if index.isValid() else self.root
return node.flags(index)
def appendRow(self, item):
row = len(self.root.children())
self.beginInsertRows(QtCore.QModelIndex(), row, row)
self.root.children().append(item)
self.endInsertRows()
class TreeView(QtWidgets.QTreeView):
def __init__(self, parent=None):
super(TreeView, self).__init__(parent)
self._model = Model()
self.setModel(self._model)
self.setSelectionMode(self.ExtendedSelection)
# self.setDropIndicatorShown(False)
self.setEditTriggers(self.DoubleClicked | self.SelectedClicked | self.EditKeyPressed)
def model(self) -> Model:
return self._model
sys.excepthook = sys.__excepthook__
app = QtWidgets.QApplication(sys.argv)
widget = TreeView()
model = widget.model()
for i in range(2):
model.appendRow(Item(model.root))
widget.show()
widget.setAttribute(QtCore.Qt.WA_DeleteOnClose)
sys.exit(app.exec_())
Solution
It seems that the docs is not clear and does not exactly match the implementation, in the implementation the number of columns in the view is dependent on the horizontal QHeaderView, and the horizontal QHeaderView uses the number of columns of the root that is the invisible item, ie the number of columns should be given by Root(), and since Root() does not overwrite the columnCount() it will have the value of 1 by default (although for me the columnCount() of Node must be 0 and children() must return a empty list), so the solution is set to 2 in Root columnCount().
import sys
import typing
from PyQt5 import QtCore, QtWidgets
class Node:
def __init__(self, parent=None):
self.parent = parent # type: Node
self.name : str
def children(self) -> list:
return list()
def hasChildren(self):
return bool(self.children())
def getData(self, index: QtCore.QModelIndex):
if index.column() == 0:
return self.name
def setData(self, val, index: QtCore.QModelIndex):
if index.column() == 0:
self.name = val
def columnCount(self):
return 0
def rowCount(self):
children = self.children()
return len(children)
def flags(self, index: QtCore.QModelIndex):
if index.column() == 0:
return (QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEditable)
else:
return QtCore.Qt.NoItemFlags
class Property(Node):
def __init__(self, parent, label, value):
super().__init__(parent)
self.label = label
self.value = value
def getData(self, index: QtCore.QModelIndex):
col = index.column()
if col == 0:
return self.label
elif col == 1:
return self.value
def setData(self, val, index: QtCore.QModelIndex):
if index.column() == 1:
self.value = val
def flags(self, index: QtCore.QModelIndex):
col = index.column()
if col == 0:
return QtCore.Qt.ItemIsEnabled
elif col == 1:
return QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsEditable | QtCore.Qt.ItemIsEditable
def columnCount(self):
return 1
class Item(Node):
def __init__(self, parent):
super().__init__(parent)
self.name = 'Item'
self.p1 = Property(self, 'string', 'text')
self.p2 = Property(self, 'float', 1.2)
def children(self):
return [self.p1, self.p2]
def columnCount(self):
return 2
class Root(Node):
def __init__(self):
super().__init__(parent=None)
self._children = list()
def children(self):
return self._children
def columnCount(self):
return 2
class Model(QtCore.QAbstractItemModel):
def __init__(self):
super().__init__()
self.root = Root()
def index(self, row: int, column: int, parent: QtCore.QModelIndex = ...) -> QtCore.QModelIndex:
if not self.hasIndex(row, column, parent):
return QtCore.QModelIndex()
node = parent.internalPointer() if parent.isValid() else self.root
if node.children:
return self.createIndex(row, column, node.children()[row])
else:
return QtCore.QModelIndex()
def parent(self, child: QtCore.QModelIndex) -> QtCore.QModelIndex:
if not child.isValid():
return QtCore.QModelIndex()
node = child.internalPointer() # type: Node
if node.parent and node.parent.parent:
row = node.parent.parent.children().index(node.parent)
return self.createIndex(row, 0, node.parent)
else:
return QtCore.QModelIndex()
def rowCount(self, parent: QtCore.QModelIndex = ...) -> int:
node = parent.internalPointer() if parent.isValid() else self.root
children = node.children()
return len(children) if children else 0
def columnCount(self, parent: QtCore.QModelIndex = ...) -> int:
node = parent.internalPointer() if parent.isValid() else self.root
print(f'{node.__class__.__name__} column count: ', node.columnCount()) # shows that column count 2 is returned, when items are expanded
# return 2 # 2nd column only shows up if I just always return 2
return node.columnCount() # view only shows 1 columns
def hasChildren(self, parent: QtCore.QModelIndex = ...) -> bool:
node = parent.internalPointer() if parent.isValid() else self.root
return node.hasChildren()
def data(self, index: QtCore.QModelIndex, role: int = ...):
if index.isValid() and role in (QtCore.Qt.DisplayRole, QtCore.Qt.EditRole):
node = index.internalPointer() # type: Node
return node.getData(index)
else:
return None
def setData(self, index: QtCore.QModelIndex, value: typing.Any, role: int = ...) -> bool:
if role in (QtCore.Qt.EditRole,):
node = index.internalPointer() # type: Node
node.setData(value, index)
self.dataChanged.emit(index, index)
return True
else:
return False
def flags(self, index: QtCore.QModelIndex):
node = index.internalPointer() if index.isValid() else self.root
return node.flags(index)
def appendRow(self, item):
row = len(self.root.children())
self.beginInsertRows(QtCore.QModelIndex(), row, row)
self.root.children().append(item)
self.endInsertRows()
class TreeView(QtWidgets.QTreeView):
def __init__(self, parent=None):
super(TreeView, self).__init__(parent)
self._model = Model()
self.setModel(self._model)
self.setSelectionMode(self.ExtendedSelection)
# self.setDropIndicatorShown(False)
self.setEditTriggers(self.DoubleClicked | self.SelectedClicked | self.EditKeyPressed)
def model(self) -> Model:
return self._model
sys.excepthook = sys.__excepthook__
app = QtWidgets.QApplication(sys.argv)
widget = TreeView()
model = widget.model()
for i in range(2):
model.appendRow(Item(model.root))
widget.show()
widget.setAttribute(QtCore.Qt.WA_DeleteOnClose)
sys.exit(app.exec_())