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@@ -9,15 +9,18 @@ to close windows.
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\wxheading{What is the sequence of events in a window deletion?}
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When the user clicks on the system close button or system close command,
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in a frame or a dialog, wxWindows calls \helpref{wxWindow::Close}{wxwindowclose}.
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in a frame or a dialog, wxWindows calls \helpref{wxWindow::Close}{wxwindowclose}. This
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in turn generates an EVT\_CLOSE event: see \helpref{wxWindow::OnCloseWindow}{wxwindowonclosewindow}.
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This function then generates a \helpref{wxCloseEvent}{wxcloseevent} event which
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can be handled by the application (by using an EVT\_CLOSE event table entry). It is the duty of the application to
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define a suitable event handler, and decide whether or not to destroy the window.
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If the application is for some reason forcing the application to close,
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the window should always be destroyed, otherwise there is the option to
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It is the duty of the application to define a suitable event handler, and
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decide whether or not to destroy the window.
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If the application is for some reason forcing the application to close
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(\helpref{wxCloseEvent::CanVeto}{wxcloseeventcanveto} returns FALSE), the window should always be destroyed, otherwise there is the option to
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ignore the request, or maybe wait until the user has answered a question
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before deciding whether it's safe to close.
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before deciding whether it's safe to close. The handler for EVT\_CLOSE should
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signal to the calling code if it does not destroy the window, by calling
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\helpref{wxCloseEvent::Veto}{wxcloseeventveto}. Calling this provides useful information
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to the calling code.
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The wxCloseEvent handler should only call \helpref{wxWindow::Destroy}{wxwindowdestroy} to
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delete the window, and not use the {\bf delete} operator. This is because
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@@ -26,24 +29,28 @@ since otherwise there is the danger that events will be sent to a non-existent w
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\wxheading{How can the application close a window itself?}
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Your application can use the \helpref{wxWindow::Close}{wxwindowclose} event just as
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the framework does. Pass a TRUE argument to this function to tell the event handler
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that we definitely want to delete the frame.
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Your application can either use \helpref{wxWindow::Close}{wxwindowclose} event just as
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the framework does, or it can call \helpref{wxWindow::Destroy}{wxwindowdestroy} directly.
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If using Close(), you can pass a TRUE argument to this function to tell the event handler
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that we definitely want to delete the frame and it cannot be vetoed.
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If for some reason you don't wish to use the {\bf Close} function to delete a window, at least use
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the {\bf Destroy} function so that wxWindows can decide when it's safe to delete the window.
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The advantage of using Close instead of Destroy is that it will call any clean-up code
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defined by the EVT\_CLOSE handler; for example it may close a document contained in
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a window after first asking the user whether the work should be saved. Close can be vetoed
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by this process (return FALSE), whereas Destroy definitely destroys the window.
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\wxheading{What is the default behaviour?}
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By default, the close event handlers for wxFrame and wxDialog
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both call the old \helpref{wxWindow::OnClose}{wxwindowonclose} handler
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for backward compatibility. So you can still use the old form if you wish.
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In addition, the default close event handler for wxDialog simulates a Cancel command,
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The default close event handler for wxDialog simulates a Cancel command,
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generating a wxID\_CANCEL event. Since the handler for this cancel event might
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itself call {\bf Close}, there is a check for infinite looping.
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itself call {\bf Close}, there is a check for infinite looping. The default handler
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for wxID\_CANCEL hides the dialog (if modeless) or calls EndModal(wxID\_CANCEL) (if modal).
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In other words, by default, the dialog is not destroyed (it might have been created
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on the stack, so the assumption of dynamic creation cannot be made).
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Under Windows, wxDialog also defines a handler for \helpref{wxWindow::OnCharHook}{wxwindowoncharhook} that
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The default close event handler for wxFrame destroys the frame using Destroy().
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Under Windows, wxDialog defines a handler for \helpref{wxWindow::OnCharHook}{wxwindowoncharhook} that
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generates a Cancel event if the Escape key has been pressed.
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\wxheading{What should I do when the user calls up Exit from a menu?}
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@@ -63,9 +70,6 @@ In wxWindows 1.xx, the {\bf OnClose} function did not actually delete 'this', bu
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to the calling function (either {\bf Close}, or the wxWindows framework) to delete
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or not delete the window.
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You can still use this function unchanged in 2.0, but it's worth upgrading to
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the new method in case future versions of wxWindows does not support the old one.
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To update your code, you should provide an event table entry in your frame or
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dialog, using the EVT\_CLOSE macro. The event handler function might look like this:
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@@ -73,22 +77,13 @@ dialog, using the EVT\_CLOSE macro. The event handler function might look like t
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\begin{verbatim}
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void MyFrame::OnCloseWindow(wxCloseEvent& event)
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{
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// If the application forces the deletion,
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// obey without question.
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if (event.GetForce())
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{
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this->Destroy();
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return;
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}
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// Otherwise...
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if (MyDataHasBeenModified())
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{
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wxMessageDialog* dialog = new wxMessageDialog(this,
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"Save changed data?", "My app", wxYES_NO|wxCANCEL);
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int ans = dialog->ShowModal();
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dialog->Close(TRUE);
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dialog->Destroy();
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switch (ans)
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{
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@@ -101,6 +96,10 @@ dialog, using the EVT\_CLOSE macro. The event handler function might look like t
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break;
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case wxID_CANCEL: // Do nothing - so don't quit app.
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default:
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if (!event.CanVeto()) // Test if we can veto this deletion
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this->Destroy(); // If not, destroy the window anyway.
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else
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event.Veto(); // Notify the calling code that we didn't delete the frame.
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break;
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}
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}
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@@ -111,7 +110,8 @@ dialog, using the EVT\_CLOSE macro. The event handler function might look like t
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\wxheading{How do I exit the application gracefully?}
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A wxWindows application automatically exits when the designated top window, or the
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last frame or dialog, is destroyed.
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last frame or dialog, is destroyed. Put any application-wide cleanup code in \helpref{wxApp::OnExit}{wxapponexit} (this
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is a virtual function, not an event handler).
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\wxheading{Do child windows get deleted automatically?}
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Julian Smart