.. include:: headings.inc .. _window deletion: ============================================= |phoenix_title| **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. Sequence of Events During Window Deletion ----------------------------------------- When the user clicks on the system close button or system close command, in a frame or a dialog, wxPython calls :meth:`wx.Window.Close`. This in turn generates an ``wx.EVT_CLOSE`` event: see :ref:`wx.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 ( :meth:`wx.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 ``wx.EVT_CLOSE`` should signal to the calling code if it does not destroy the window, by calling :meth:`wx.CloseEvent.Veto`. Calling this provides useful information to the calling code. The :ref:`wx.CloseEvent` handler should only call :meth:`wx.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 :meth:`wx.Window.Destroy` if you want to be certain that the window is destroyed. Closing Windows --------------- Your application can either use :meth:`wx.Window.Close` event just as the framework does, or it can call :meth:`wx.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 ``wx.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. Default Window Close Behaviour ------------------------------ The default close event handler for :ref:`wx.Dialog` simulates a ``Cancel`` command, generating a ``wx.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 ``wx.ID_CANCEL`` hides the dialog (if modeless) or calls `EndModal(wx.ID_CANCEL)` (if modal). In other words, by default, the dialog is not destroyed. The default close event handler for :ref:`wx.Frame` destroys the frame using `Destroy()`. User Calls to Exit From a Menu ------------------------------ What should I do when the user calls up `Exit` from a menu? You can simply call :meth:`wx.Window.Close` on the frame. This will invoke your own close event handler which may destroy the frame. You can do checking to see if your application can be safely exited at this point, either from within your close event handler, or from within your exit menu command handler. For example, you may wish to check that all files have been saved. Give the user a chance to save and quit, to not save but quit anyway, or to cancel the exit command altogether. Exiting the Application Gracefully ---------------------------------- A wxPython application automatically exits when the last top level window (:ref:`wx.Frame` or :ref:`wx.Dialog`), is destroyed. Put any application-wide cleanup code in :meth:`wx.AppConsole.OnExit` (this is a method, not an event handler). Automatic Deletion of Child Windows ----------------------------------- 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. Other Kinds of Windows ---------------------- 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 :meth:`wx.Window.Destroy` method instead of the `del` operator when deleting these kinds of windows explicitly.