Window Deletion Overview¶Window deletion can be a confusing subject, so this overview is provided to help make it clear when and how you delete windows, or respond to user requests to close windows.
When the user clicks on the system close button or system close command, in a frame or a dialog, wxPython calls Window.Close. This in turn generates an EVT_CLOSE event: see CloseEvent.
It is the duty of the application to define a suitable event handler, and decide whether or not to destroy the window. If the application is for some reason forcing the application to close ( CloseEvent.CanVeto returns False), the window should always be destroyed, otherwise there is the option to ignore the request, or maybe wait until the user has answered a question before deciding whether it is safe to close. The handler for EVT_CLOSE should signal to the calling code if it does not destroy the window, by calling CloseEvent.Veto. Calling this provides useful information to the calling code.
The CloseEvent handler should only call Window.Destroy to delete the window, and not use the del operator. This is because for some window classes, wxPython delays actual deletion of the window until all events have been processed, since otherwise there is the danger that events will be sent to a non-existent window.
As reinforced in the next section, calling Close does not guarantee that the window will be destroyed. Call Window.Destroy if you want to be certain that the window is destroyed.
Your application can either use Window.Close event just as the framework does, or it can call Window.Destroy directly. If using Close(), you can pass a True argument to this function to tell the event handler that we definitely want to delete the frame and it cannot be vetoed.
The advantage of using Close instead of Destroy is that it will call any clean-up code defined by the EVT_CLOSE handler; for example it may close a document contained in a window after first asking the user whether the work should be saved. Close can be vetoed by this process (return False), whereas Destroy definitely destroys the window.
The default close event handler for Dialog simulates a Cancel command, generating a ID_CANCEL event. Since the handler for this cancel event might itself call Close, there is a check for infinite looping. The default handler for ID_CANCEL hides the dialog (if modeless) or calls EndModal(ID_CANCEL) (if modal). In other words, by default, the dialog is not destroyed.
The default close event handler for Frame destroys the frame using Destroy().
A wxPython application automatically exits when the last top level window ( Frame or Dialog), is destroyed. Put any application-wide cleanup code in AppConsole.OnExit (this is a method, not an event handler).
Child windows are deleted from within the parent destructor. This includes any children that are themselves frames or dialogs, so you may wish to close these child frame or dialog windows explicitly from within the parent close handler.
So far we’ve been talking about ‘managed’ windows, i.e. frames and dialogs. Windows with parents, such as controls, don’t have delayed destruction and don’t usually have close event handlers, though you can implement them if you wish. For consistency, continue to use the Window.Destroy method instead of the del operator when deleting these kinds of windows explicitly.
