moving forward
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52051 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
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@page overview_windowdeletion Window deletion overview
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Classes: #wxCloseEvent, #wxWindow
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Window deletion can be a confusing subject, so this overview is provided
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to help make it clear when and how you delete windows, or respond to user requests
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to close windows.
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@b What is the sequence of events in a window deletion?
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@section sequence 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, wxWidgets calls wxWindow::Close. This
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in turn generates an EVT_CLOSE event: see #wxCloseEvent.
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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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@@ -27,42 +31,56 @@
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signal to the calling code if it does not destroy the window, by calling
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wxCloseEvent::Veto. Calling this provides useful information
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to the calling code.
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The wxCloseEvent handler should only call wxWindow::Destroy to
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delete the window, and not use the @b delete operator. This is because
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for some window classes, wxWidgets delays actual deletion of the window until all events have been processed,
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since otherwise there is the danger that events will be sent to a non-existent window.
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As reinforced in the next section, calling Close does not guarantee that the window
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will be destroyed. Call wxWindow::Destroy if you want to be
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certain that the window is destroyed.
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@b How can the application close a window itself?
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@section close How can the application close a window itself?
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Your application can either use wxWindow::Close event just as
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the framework does, or it can call wxWindow::Destroy 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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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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@b What is the default behaviour?
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@section default What is the default behaviour?
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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 @b 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 @e 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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The default close event handler for wxFrame destroys the frame using Destroy().
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@b What should I do when the user calls up Exit from a menu?
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@section exit What should I do when the user calls up Exit from a menu?
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You can simply call wxWindow::Close on the frame. This
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will invoke your own close event handler which may destroy the frame.
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You can do checking to see if your application can be safely exited at this point,
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either from within your close event handler, or from within your exit menu command
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handler. For example, you may wish to check that all files have been saved.
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Give the user a chance to save and quit, to not save but quit anyway, or to cancel
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the exit command altogether.
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@b What should I do to upgrade my 1.xx OnClose to 2.0?
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@section upgrade What should I do to upgrade my 1.xx OnClose to 2.0?
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In wxWidgets 1.xx, the @b OnClose function did not actually delete 'this', but signaled
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to the calling function (either @b Close, or the wxWidgets framework) to delete
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or not delete the window.
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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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@@ -98,16 +116,21 @@
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}
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@endcode
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@b How do I exit the application gracefully?
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@section exit_app How do I exit the application gracefully?
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A wxWidgets application automatically exits when the last top level window
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(#wxFrame or #wxDialog), is destroyed. Put
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any application-wide cleanup code in wxApp::OnExit (this
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is a virtual function, not an event handler).
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@b Do child windows get deleted automatically?
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@section deletion Do child windows get deleted automatically?
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Yes, child windows are deleted from within the parent destructor. This includes any children
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that are themselves frames or dialogs, so you may wish to close these child frame or dialog windows
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explicitly from within the parent close handler.
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@b What about other kinds of window?
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@section window_kinds What about other kinds of window?
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So far we've been talking about 'managed' windows, i.e. frames and dialogs. Windows
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with parents, such as controls, don't have delayed destruction and don't usually have
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close event handlers, though you can implement them if you wish. For consistency,
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@@ -10,22 +10,24 @@
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@page overview_windowids Window IDs overview
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@b See Also
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@seealso
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#wxIdManager
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wxWindow::NewControlId
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wxWindow::UnreserveControlId
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#Introduction
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@ref windowidstypes_overview
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@ref windowidsusing_overview
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@li @ref introduction
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@li @ref overview_windowidstypes
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@li @ref overview_windowidsusing
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@section windowidsoverviewintro Introduction
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@section introduction Introduction
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Various contols and other parts of wxWidgets need an ID. Sometimes the
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ID may be directly provided by the use or have a predefined value, such as
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@c wxID_OPEN. Often, however, the value of the ID is unimportant and is
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created automatically by calling wxWindow::NewControlId
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or by passing @c wxID_ANY as the ID of an object.
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There are two ways to generate an ID. One way, is to start at a negative number,
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and for each new ID, return the next smallest number. This is fine for systems
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that can used the full range of negative numbers for an ID, as this provides
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@@ -36,6 +38,7 @@
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If the program runs long enough, depending on the program itself, using this first
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method would cause the IDs to wrap around into the positive ID range and cause possible
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clashes with any directly specified ID values.
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The other way is to keep track of the IDs returned by wxWindow::NewControlId
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and don't return them again until the ID is completely free and not being used by
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any other objects. This will make sure that the ID values do not clash with one
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@@ -43,7 +46,7 @@
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that can possibly be returned by wxWindow::NewControlId.
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Other IDs are not reference counted.
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@section windowidsoverviewtypes Data types
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@section overview_windowidstypes Data types
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A wxWindowID is just the integer type for a window ID. It should be used almost
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everywhere. To help keep track of the count for the automatically generated IDs,
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@@ -54,15 +57,17 @@
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As the wxWindowIDRef gets destroyed or its value changes, it will decrease the count
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of the used ID. When there are no more wxWindowIDRef types with the created ID, the
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ID is considered free and can then be used again by wxWindow::NewControlId.
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If a created ID is not assigned to a wxWindowIDRef, then it remains reserved until it
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is unreserved manually with wxWindow::UnreserveControlId.
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However, if it is assigned to a wxWindowIDRef, then it will be unreserved automatically
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and will be considered free when the count is 0, and should NOT be manually unreserved.
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wxWindowIDRef can store both automatic IDs from wxWindow::NewControlId
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as well as normal IDs. Reference counting is only done for the automatic IDs. Also,
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wxWindowIDRef has conversion operators that allow it to be treated just like a wxWindowID.
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@section windowidsoverviewusing Using wxWindowIDRef
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@section overview_windowidsusing Using wxWindowIDRef
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A wxWindowIDRef should be used in place of a wxWindowID where you want to make sure the
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ID is not created again by wxWindow::NewControlId
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