75 lines
3.6 KiB
C
75 lines
3.6 KiB
C
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/////////////////////////////////////////////////////////////////////////////
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// Name: windowids.h
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// Purpose: topic overview
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// Author: wxWidgets team
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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/**
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@page overview_windowids Window IDs
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@tableofcontents
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Various controls and other parts of wxWidgets need an ID. Sometimes the ID may
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be directly provided by the user 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 created
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automatically by calling wxWindow::NewControlId or by passing @c wxID_ANY as
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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
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number, and for each new ID, return the next smallest number. This is fine for
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systems that can use the full range of negative numbers for IDs, as this
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provides more than enough IDs and it would take a very very long time to run
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out and wrap around. However, some systems cannot use the full range of the
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ID value. Windows, for example, can only use 16 bit IDs, and only has about
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32000 possible automatic IDs that can be generated by wxWindow::NewControlId.
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If the program runs long enough, depending on the program itself, using this
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first method would cause the IDs to wrap around into the positive ID range and
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cause possible 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
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by any other objects. This will make sure that the ID values do not clash with
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one another. This is accomplished by keeping a reference count for each of the
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IDs that can possibly be returned by wxWindow::NewControlId. Other IDs are not
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reference counted.
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@see wxIdManager, wxWindow::NewControlId(), wxWindow::UnreserveControlId()
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@section overview_windowids_type Data Types
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A wxWindowID is just the integer type for a window ID. It should be used
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almost everywhere. To help keep track of the count for the automatically
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generated IDs, a new type, wxWindowIDRef exists, that can take the place of
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wxWindowID where needed. When an ID is first created, it is marked as reserved.
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When assigning it to a wxWindowIDRef, the usage count of the ID is increased,
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or set to 1 if it is currently reserved. Assigning the same ID to several
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wxWindowIDRefs will keep track of the count. As the wxWindowIDRef gets
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destroyed or its value changes, it will decrease the count of the used ID. When
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there are no more wxWindowIDRef types with the created ID, the ID is considered
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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
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until it is unreserved manually with wxWindow::UnreserveControlId. However, if
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it is assigned to a wxWindowIDRef, then it will be unreserved automatically and
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will be considered free when the count is 0, and should NOT be manually
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unreserved.
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wxWindowIDRef can store both automatic IDs from wxWindow::NewControlId and
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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
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wxWindowID.
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@section overview_windowids_using Using wxWindowIDRef
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A wxWindowIDRef should be used in place of a wxWindowID where you want to make
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sure the ID is not created again by wxWindow::NewControlId at least until the
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wxWindowIDRef is destroyed, usually when the associated object is destroyed.
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This is done already for windows, menu items, and tool bar items. It should
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only be used in the main thread, as it is not thread safe.
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*/
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