I was recently asked about how to implement drag-and-drop of items in a wx.ListCtrl or in ObjectListView. Unfortunately, neither control has this built-in although I did find an article on the wxPython wiki that demonstrated one way to do drag-and-drop of the items in a ListCtrl.

However, I did think that implementing some buttons to move items around in an ObjectListView widget should be fairly easy to implement. So that’s what this article will be focusing on.

Changing Item Order

If you don’t have wxPython and ObjectListView installed, then you will want to use pip to install them:

pip install wxPython objectlistview

Once that is done, open up your favorite text editor or IDE and enter the following code:

import wx
from ObjectListView import ObjectListView, ColumnDefn


class Book(object):
    """
    Model of the Book object
    Contains the following attributes:
    'ISBN', 'Author', 'Manufacturer', 'Title'
    """

    def __init__(self, title, author, isbn, mfg):
        self.isbn = isbn
        self.author = author
        self.mfg = mfg
        self.title = title

    def __repr__(self):
        return "<Book: {title}>".format(title=self.title)


class MainPanel(wx.Panel):

    def __init__(self, parent):
        wx.Panel.__init__(self, parent=parent, id=wx.ID_ANY)
        self.current_selection = None
        self.products = [Book("wxPython in Action", "Robin Dunn",
                              "1932394621", "Manning"),
                         Book("Hello World", "Warren and Carter Sande",
                              "1933988495", "Manning"),
                         Book("Core Python Programming", "Wesley Chun",
                             "0132269937", "Prentice Hall"),
                         Book("Python Programming for the Absolute Beginner",
                              "Michael Dawson", "1598631128",
                              "Course Technology"),
                         Book("Learning Python", "Mark Lutz",
                              "0596513984", "O'Reilly")
                         ]

        self.dataOlv = ObjectListView(self, wx.ID_ANY, 
                                      style=wx.LC_REPORT|wx.SUNKEN_BORDER)
        self.setBooks()

        # Allow the cell values to be edited when double-clicked
        self.dataOlv.cellEditMode = ObjectListView.CELLEDIT_SINGLECLICK

        # create up and down buttons
        up_btn = wx.Button(self, wx.ID_ANY, "Up")
        up_btn.Bind(wx.EVT_BUTTON, self.move_up)

        down_btn = wx.Button(self, wx.ID_ANY, "Down")
        down_btn.Bind(wx.EVT_BUTTON, self.move_down)

        # Create some sizers
        mainSizer = wx.BoxSizer(wx.VERTICAL)

        mainSizer.Add(self.dataOlv, 1, wx.ALL|wx.EXPAND, 5)
        mainSizer.Add(up_btn, 0, wx.ALL|wx.CENTER, 5)
        mainSizer.Add(down_btn, 0, wx.ALL|wx.CENTER, 5)
        self.SetSizer(mainSizer)

    def move_up(self, event):
        """
        Move an item up the list
        """        
        self.current_selection = self.dataOlv.GetSelectedObject()
        data = self.dataOlv.GetObjects()
        if self.current_selection:
            index = data.index(self.current_selection)
            if index > 0:
                new_index = index - 1
            else:
                new_index = len(data)-1
            data.insert(new_index, data.pop(index))
            self.products = data
            self.setBooks()
            self.dataOlv.Select(new_index)

    def move_down(self, event):
        """
        Move an item down the list
        """
        self.current_selection = self.dataOlv.GetSelectedObject()
        data = self.dataOlv.GetObjects()
        if self.current_selection:
            index = data.index(self.current_selection)
            if index < len(data) - 1:
                new_index = index + 1
            else:
                new_index = 0
            data.insert(new_index, data.pop(index))
            self.products = data
            self.setBooks()
            self.dataOlv.Select(new_index)

    def setBooks(self):
        self.dataOlv.SetColumns([
            ColumnDefn("Title", "left", 220, "title"),
            ColumnDefn("Author", "left", 200, "author"),
            ColumnDefn("ISBN", "right", 100, "isbn"),
            ColumnDefn("Mfg", "left", 180, "mfg")
        ])

        self.dataOlv.SetObjects(self.products)


class MainFrame(wx.Frame):
    def __init__(self):
        wx.Frame.__init__(self, parent=None, id=wx.ID_ANY, 
                          title="ObjectListView Demo", size=(800,600))
        panel = MainPanel(self)
        self.Show()


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

The code we care about most in this example are the move_up() and move_down()methods. Each of these methods will check to see if you have an item in the ObjectListView widget selected. It will also grab the current contents of the widgets. If you have an item selected, then it will grab that item’s index from the ObjectListView widget’s data that we grabbed when we called GetObjects(). Then we can use that index to determine whether we should increment (move_down) or decrement (move_up) its index depending on which of the buttons we press.

After we update the list with the changed positions, then we update self.products, which is our class variable that we use in the setBooks() to update our ObjectListView widget. Finally we actually call setBooks() and we reset the selection since our original selection moved.

Wrapping Up

I thought this was a neat little project that didn’t take very long to put together. I will note that there is at least one issue with this implementation and that is that it doesn’t work correctly when you select multiple items in the control. You could probably fix this by disabling multiple selection in your ObjectListView widget or by figuring out the logic to make it work with multiple selections. But I will leave that up the reader to figure out. Have fun an happy coding!