Letting Users Change a wx.ComboBox's Contents in wxPython

This week I came across someone who was wondering if there was a way to allow the user to edit the contents of a wx.ComboBox. By editing the contents, I mean change the names of the pre-existing choices that the ComboBox contains, not adding new items to the widget.

While editing the contents of the selected item in a ComboBox works out of the box, the widget will not save those edits automatically. So if you edit something and then choose a different option in the ComboBox, the edited item will revert back to whatever it was previously and your changes will be lost.

Let's find out how you can create a ComboBox that allows this functionality!

Creating GUI Applications with wxPython Purchase now on Leanpub or Amazon

Changing a ComboBox

The first step when trying something new out is to write some code. You'll need to create an instance of wx.ComboBox and pass it a list of choices as well as set the default choice. Of course, you cannot create a single widget in isolation. The widget must be inside of a parent widget. In wxPython, you almost always want the parent to be a wx.Panel that is inside of a wx.Frame.

Let's write some code and see how this all lays out:

import wx

class MainPanel(wx.Panel):

    def __init__(self, parent):
        super().__init__(parent)

        self.cb_value = 'One'

        self.combo_contents = ['One', 'Two', 'Three']
        self.cb = wx.ComboBox(self, choices=self.combo_contents,
                              value=self.cb_value, size=(100, -1))

        self.cb.Bind(wx.EVT_TEXT, self.on_text_change)
        self.cb.Bind(wx.EVT_COMBOBOX, self.on_selection)

    def on_text_change(self, event):
        current_value = self.cb.GetValue()
        if current_value != self.cb_value and current_value not in self.combo_contents:
            # Value has been edited
            index = self.combo_contents.index(self.cb_value)
            self.combo_contents.pop(index)
            self.combo_contents.insert(index, current_value)
            self.cb.SetItems(self.combo_contents)
            self.cb.SetValue(current_value)
            self.cb_value = current_value
            
    def on_selection(self, event):
        self.cb_value = self.cb.GetValue()

class MainFrame(wx.Frame):

    def __init__(self):
        super().__init__(None, title='ComboBox Changing Demo')
        panel = MainPanel(self)
        self.Show()


if __name__ == "__main__":
    app = wx.App(False)
    frame = MainFrame()
    app.MainLoop()

The main part of the code that you are interested in is inside the MainPanel class. Here you create the widget, set its choices list and a couple of other parameters. Next you will need to bind the ComboBox to two events:

• wx.EVT_TEXT - For text change events
• wx.EVT_COMBOBOX - For changing item selection events

The first event, wx.EVT_TEXT, is fired when you change the text in the widget by typing and it also fires when you change the selection. The other event only fires when you change selections. The wx.EVT_TEXT event fires first, so it has precedence over wx.EVT_COMBOBOX.

When you change the text, on_text_change() is called. Here you will check if the current value of the ComboBox matches the value that you expect it to be. You also check to see if the current value matches the choice list that is currently set. This allows you to see if the user has changed the text. If they have, then you want to grab the index of the currently selected item in your choice list.

Then you use the list's pop() method to remove the old string and the insert() method to add the new string in its place. Now you need to call the widget's SetItems() method to update its choices list. Then you set its value to the new string and update the cb_value instance variable so you can check if it changes again later.

The on_selection() method is short and sweet. All it does is update cb_value to whatever the current selection is.

Give the code a try and see how it works!

Wrapping Up

Adding the ability to allow the user to update the wx.ComboBox's contents isn't especially hard. You could even subclass wx.ComboBox and create a version where it does that for you all the time. Another enhancement that might be fun to add is to have the widget load its choices from a config file or a JSON file. Then you could update on_text_change() to save your changes to disk and then your application could save the choices and reload them the next time you start your application.

Have fun and happy coding!