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Name: [002] Ian Ozsvald
Member: 106 months
Authored: 181 videos
Description: I am the co-founder of ShowMeDo (see http://showmedo.com/about), author of `The Screencasting Handbook <http://thescreencastinghandbook.com>`_ and the founder of the professional screencast production company `ProCasts <http://procasts.co.uk>`_: .. image:: http://procasts.co.uk/media/procasts_sma ...

Add Menus, wx Ids, Binding [ID:528] (4/14)

in series: Build a wxPython Image Viewer

(Showmedo is undergoing major changes. To report any problems viewing the videos please email us and include browser and OS specifics. Cheers - Kyran.)

We add a MenuBar with some Menu items. When adding Menus or other widgets you always have to specify an 'id' and there are multiple (slightly confusing!) ways of creating them...to set our wx Ids we discuss wx's '-1', wx.ID_ANY, wx.NewId() and managing your own Ids. I provide the heuristic of always using '-1' for your Ids unless you need more control.

We test wx's new Id using object.GetId() and we use Wingware's Source Assistant feature to look at some wx help text.

Menus aren't much use if they can't control anything so we move on to using self.Bind(...) to attach a menu event to a function - and we look at what happens if the specified function doesn't exist when we try to Bind to it.

Finally we establish the self.OnExit() method and use self.Destory() to cleanly exit the application. We also look at using 'print' to follow the flow of events in the application.

import wx

MAIN_WINDOW_DEFAULT_SIZE = (300,200)

class Frame(wx.Frame):
    
    def __init__(self, parent, id, title):
        style=wx.DEFAULT_FRAME_STYLE ^ (wx.RESIZE_BORDER) # XOR to remove the resizeable border        
        wx.Frame.__init__(self, parent, id, title=title, size=MAIN_WINDOW_DEFAULT_SIZE, style=style)
        self.Center() # open in the centre of the screen
        self.panel = wx.Panel(self)
        self.panel.SetBackgroundColour('White') # make the background of the window white

        self.CreateMenuBar()

    def CreateMenuBar(self):
        "Create a menu bar with Open, Exit items"
        menuBar = wx.MenuBar()
        # Tell our Frame about this MenuBar
        self.SetMenuBar(menuBar)
        menuFile = wx.Menu()
        menuBar.Append(menuFile, '&File')
        # NOTE on wx ids - they're used everywhere, we don't care about them
        # Used to handle events and other things
        # An id can be -1 or wx.ID_ANY, wx.NewId(), your own id
        # Get the id using object.GetId()
        #fileOpenMenuItem = menuFile.Append(-1, '&Open Image', 'Open a picture')
        #print "fileOpenMenuItem.GetId()", fileOpenMenuItem.GetId()
        #self.Bind(wx.EVT_MENU, self.OnOpen, fileOpenMenuItem)

        # add a 'mirror' option, disable it for now
        # we add mirrorMenuItem to self so that we can reference it later
        #self.mirrorMenuItem = menuFile.Append(-1, '&Mirror Image', 'Mirror the image horizontally')
        #self.mirrorMenuItem.Enable(False) # we can't mirror an image until we've loaded one in, so start with 'mirror' disabled
        #self.Bind(wx.EVT_MENU, self.OnMirrorImage, self.mirrorMenuItem)
        # create a menu item for Exit and bind it to the OnExit function
        
        #exitMenuItem = menuFile.Append(-1, 'E&xit', 'Exit the viewer')        
        #self.Bind(wx.EVT_MENU, self.OnExit, exitMenuItem)
        
        # add a Help menu with an About item
        #menuHelp = wx.Menu()
        #menuBar.Append(menuHelp, '&Help')
        #helpMenuItem = menuHelp.Append(-1, '&About', 'About screen')
        #self.Bind(wx.EVT_MENU, self.OnAbout, helpMenuItem)

    def OnOpen(self, event):
        print "OnOpen called"
        
    #def OnExit(self, event):
    #    "Close the application by Destroying the object"
    #    # TRY add in your own print call here
    #    self.Destroy() # SHOW HELP SIDEBAR
        
    
class App(wx.App):
    
    def OnInit(self):
        self.frame = Frame(parent=None, id=-1, title='Image Viewer')
        self.frame.Show()
        self.SetTopWindow(self.frame)
        return True
    
if __name__ == "__main__":       
    # make an App object, set stdout to the console so we can see errors
    app = App(redirect=False)
        
    app.MainLoop()

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I had mentioned in an earlier comment I could not see the source code (the code to cut and paste out for my own use). This seems to be an issue when using Internet explorer 7 (on Vista). But switching to firefox the source code section does display. It also displays properly on Opera. I wish I knew why it does not show properly on IE, but that is not a big issue. Really like the video's, speed is fine, I hope you are getting paid by Wingware as you have me thinking about paying for their IDE.


Useful screencast, I think that the event IDs managed by wxpython is a good idea. Worrying about it at beginner fases would be clutering.


It seems my problems have gone away . . . :-)

the code from episode 4 runs just fine.

Great stuff.


Hi Lucas. There was no particular reason, I had refactored the code several times and I think I just missed this one. Out of preference I'd have used 'fileOpenMenuItem' with 'fileExitMenuItem' OR 'openMenuItem' and 'exitMenuItem', but I guess this naming just slipped through.

Well spotted :-)

Ian.


Hey Ian,

after rewatching this video, I noticed one thing while playing around with the source code:

you named the "Open" item in the "File" menu

fileOpenMenuItem

The "Exit" item in the same "File" menu is called

exitMenuItem

The "file" prefix makes sense, it signifies that the menu item is part of the file menu.

Why did you decide not to prefix the "exitMenuItem" menu item?

Lucas


Good job Ian! This video really repays playing over more than once. I like the way that you are building up the code by assembling the parts and explaining them as you go along. wxPython is a lot more complicated than regular Python, and can be confusing if the viewer tries to take in too much as once. By the way, the viewer should be aware that you can use IPython to supply docstrings:

import wx

wx.Frame.Destroy??

(although Wing is more convenient).

Jerol


This is a great series. Start to finish dev on a simple app.

Looking forward to the next installment.


Video published, thanks for contributing to ShowMeDo


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Kudos and Thanks for Ian

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