Question

Could someone show me how I could return a value from a wxPython Frame? When the use clicks close, I popup a message dialog asking him a question. I would like to return the return code of this message dialog to my calling function.

Thanks

Answer 1

Because the wxFrame has events that process via the app.MainLoop() functionality, the only way to get at the return value of a wx.Frame() is via catching an event.

The standard practice of handling events is typically from within the class which derives from wx.Window itself (e.g., Frame, Panel, etc.). Since you want code exterior to the wx.Frame to receive information that was gathered upon processing the OnClose() event, then the best way to do that is to register an event handler for your frame.

The documentation for wx.Window::PushEventHandler is probably the best resource and even the wxpython wiki has a great article on how to do this. Within the article, they register a custom handler which is an instance of "MouseDownTracker." Rather than instantiating within the PushEventHandler call, you’d want to instantiate it prior to the call so that you can retain a handle to the EventHandler derived class. That way, you can check on your derived EventHandler class-variables after the Frame has been destroyed, or even allow that derived class to do special things for you.

Here is an adaptation of that code from the wx python wiki (admittedly a little convoluted due to the requirement of handling the results of a custom event with a "calling" function):

import sys
import wx
import wx.lib.newevent
    
(MyCustomEvent, EVT_CUSTOM) = wx.lib.newevent.NewEvent()
    
class CustomEventTracker(wx.EvtHandler):
    def __init__(self, log, processingCodeFunctionHandle):
        wx.EvtHandler.__init__(self)
        self.processingCodeFunctionHandle = processingCodeFunctionHandle
        self.log = log
        EVT_CUSTOM(self, self.MyCustomEventHandler)
    
    def MyCustomEventHandler(self, evt):
        self.log.write(evt.resultOfDialog + '\n')
        self.processingCodeFunctionHandle(evt.resultOfDialog)
        evt.Skip()
    
class MyPanel2(wx.Panel):
    def __init__(self, parent, log):
        wx.Panel.__init__(self, parent)
        self.log = log
    
    def OnResults(self, resultData):
        self.log.write("Result data gathered: %s" % resultData)
    
class MyFrame(wx.Frame):
    def __init__(self, parent, ID=-1, title="", pos=wx.DefaultPosition, size=wx.DefaultSize, style=wx.DEFAULT_FRAME_STYLE):
        wx.Frame.__init__(self, parent, ID, title, pos, size, style)
        self.panel = panel = wx.Panel(self, -1, style=wx.TAB_TRAVERSAL | wx.CLIP_CHILDREN | wx.FULL_REPAINT_ON_RESIZE)
        sizer = wx.BoxSizer(wx.VERTICAL)
        sizer.Add((25, 25))
    
        row = wx.BoxSizer(wx.HORIZONTAL)
        row.Add((25,1))
        m_close = wx.Button(self.panel, wx.ID_CLOSE, "Close")
        m_close.Bind(wx.EVT_BUTTON, self.OnClose)
        row.Add(m_close, 0, wx.ALL, 10)
        sizer.Add(row)
        self.panel.SetSizer(sizer)
    
    def OnClose(self, evt):
        dlg = wx.MessageDialog(self, "Do you really want to close this frame?", "Confirm Exit", wx.OK | wx.CANCEL | wx.ICON_QUESTION)
        result = dlg.ShowModal()
        dlg.Destroy()
        if result == wx.ID_CANCEL:
            event = MyCustomEvent(resultOfDialog="User Clicked CANCEL")
            self.GetEventHandler().ProcessEvent(event)
        else: # result == wx.ID_OK
            event = MyCustomEvent(resultOfDialog="User Clicked OK")
            self.GetEventHandler().ProcessEvent(event)
        self.Destroy()
    
app = wx.App(False)
f2 = wx.Frame(None, title="Frame 1 (for feedback)", size=(400, 350))
p2 = MyPanel2(f2, sys.stdout)
f2.Show()
eventTrackerHandle = CustomEventTracker(sys.stdout, p2.OnResults)
f1 = MyFrame(None, title="PushEventHandler Tester (deals with on close event)", size=(400, 350))
f1.PushEventHandler(eventTrackerHandle)
f1.Show()
app.MainLoop()