Editing Cell Values

ListCtrls are normally used for displaying information. The standard ListCtrl allows the value at column 0 (the primary cell) to be edited, but nothing beyond that. ObjectListView allows all cells to be edited. Depending on how the data for a cell is sourced, the edited values can be automagically written back into the model object.

The “editability” of an ObjectListView is controlled by the cellEditMode attribute. This attribute can be set to one of the following values:

  • ObjectListView.CELLEDIT_NONE

    Cell editing is not allowed on the control This is the default.

  • ObjectListView.CELLEDIT_SINGLECLICK

    Single clicking on any subitem cell begins an edit operation on that cell. Single clicking on the primary cell does not start an edit operation. It simply selects the row. Pressing F2 edits the primary cell.

  • ObjectListView.CELLEDIT_DOUBLECLICK

    Double clicking any cell starts an edit operation on that cell, including the primary cell. Pressing F2 edits the primary cell.

  • ObjectListView.CELLEDIT_F2ONLY

    Pressing F2 edits the primary cell. Tab/Shift-Tab can be used to edit other cells. Clicking does not start any editing.

Individual columns can be marked as editable via the isEditable attribute (default value is True), though this only has meaning once the ObjectListView itself is editable. If you know that the user should not be allowed to change cells in a particular column, set isEditable to False. Be aware, though, that this may create some surprises, resulting in user complaints like “How come I can’t edit this value by clicking on it like I can on all the other cells?”.

Once a cell editor is active, the normal editing conventions apply:

  • Enter or Return finishes the edit and commits the new value to the model object.
  • Escape cancels the edit.
  • Tab commits the current edit, and starts a new edit on the next editable cell.
  • Shift-Tab commits the current end, and starts a new edit on the previous editable cell.

Deciding on a cell editor

When a cell is to be edited, we need to decide what sort of editor to use.

There are three ways this decision can be made:

  1. Column based decision

Most simply, the column can be configured with a cellEditorCreator attribute. When a cell in this column is to be edited, the cellEditorCreator will be invoked. This attribute must be set to a “cell editor factory” callable. A “cell editor factory” must be a callable that accepts three parameters:

  • the ObjectListView that needs the editor
  • the index of the row to be edited
  • the index of the subitem to be edited

This factory should return a fully configured widget that can edit the value at that cell.

  1. Event based decision

If this is not enough, the programmer can have complete control over the process by listening for a cell editing starting event (ObjectListView.EVT_CELL_EDIT_STARTING). Within the handler for this event, the programmer can create and configure any sort of widget they like and then return this widget via the newEditor attribute of the event.

If the shouldConfigureEditor attribute of the event is True (this is the default), the ObjectListView will perform all the normal default configuration of the cell editor. This includes setting the controls value, positioning it correctly and hooking up any required events. If shouldConfigureEditor is False, it is assumed that all configuration has already been done and nothing else will be done to the widget.

  1. Registry based decision

Most generally, you can register a “cell editor factory” for a type of object. This is done using RegisterCreatorFunction method of the CellEditorRegistry.

For example, there is no standard editor for a wx.Colour. To handle the editing of colours, we would need a factory callable, and then to register it with the CellEditorRegistry. Which migh look something like this:

def makeColourEditor(olv, rowIndex, subItemIndex):
    odcb = OwnerDrawnEditor.ColourComboBox(olv)
    # OwnerDrawnComboxBoxes don't generate EVT_CHAR so look for keydown instead
    odcb.Bind(wx.EVT_KEY_DOWN, olv._HandleChar)
    return odcb

CellEditorRegistry().RegisterCreatorFunction(type(wx.BLACK), makeColourEditor)

By default, the cell registry is configured with editors for the following standard types: bool, int, long, str, unicode, float, datetime, date, time.

You can replace the standard editors with editors of your own devising using the registry. So if someone make a better date-time editor (yes, please!), they could use it to edit all datetime values by doing this:

import datetime
...
CellEditorRegistry().RegisterCreatorFunction(datetime.datetime, makeBetterDateTimeEditor)

Getting and Setting the Editors value

A cell editor must implement both GetValue and SetValue methods.

Once the cell editor has been created, it is given the cell’s value via the control’s SetValue method.

When the user has finished editing the value, the new value in the editor is retrieved via the GetValue method.

Updating the Model Object

Once the user has entered a new value into a cell and pressed Enter, the ObjectListView tries to store the modified value back into the model object. There are three ways this can happen:

1. ObjectListView.EVT_CELL_EDIT_FINISHING Event Handler

You can create an event handler for the EVT_CELL_EDIT_FINISHING event (see below). In that handler, you would write the code to get the modified value from the editor, put that new value into the model object, and then call Veto on the event, so that the ObjectListView knows that it doesn’t have to do anything else. You will also need to call at least RefreshItem() or RefreshObject(), so that the changes to the model object are shown in the ObjectListView.

There are cases where this is necessary, but as a general solution, it doesn’t fit my philosophy of slothfulness.

2. Via the Column’s valueSetter attribute

You can set the valueSetter attribute on the corresponding ColumnDefn. Like valueGetter, this attribute is quite flexible:

  • It can be a callable that accepts the model object and the new value:

    def updateSalary(person, newValue):
    person.SetSalary(newValue)
    if person.userId == self.currentUser.userId:
        self.NotifySupervisorOfSalaryChange()

ColumnDefn("Salary", ... valueSetter=updateSalary)

  • It can be the name of a method to be invoked,. This method must accept the new value as its sole parameter. Example:

    class Track():
    ...
    def SetDateLastPlayed(self, newValue):
        self.dateLastPlayed = newValue

ColumnDefn("Last Played", ... valueSetter="SetDateLastPlayed")

  • It can be the name of an attribute to be updated. This attribute will not be created: it must already exist. Example:

    ColumnDefn("Last Played", ... valueSetter="dateLastPlayed")

  • For dictionary like model objects, it can be the key into the dictionary. The key would commonly be a string, but it doesn’t have to be.

3. Via the Column’s valueGetter attribute

Updating the value through the value-GETTER attribute seems wrong somehow. In practice, it is neat and commonly used.

If the valueGetter attribute is the name of an attribute, or the key into a dictionary, it will very commonly be the same place where any modified value should be written.

So if a value needs to be written back into the model, and there is no valueSetter attribute, the ObjectListView will try to use the valueGetter attribute to decide how to update the model.

After the update

If the model is updated, the row will be automatically refreshed to display the new data.

If the user enters a new value, presses Enter, and the value in the ObjectListView doesn’t change, then almost certainly the ObjectListView could not automagically update the model object.

In that case, you will need to track down, which of the above three strategies should be being used, and why it is not.

How Can You Customise The Editing

To do something other than the default processing, you can listen for two events: ObjectListView.EVT_CELL_EDIT_STARTING and ObjectListView.EVT_CELL_EDIT_FINISHING.

## MORE HERE ##