docs/doxygen/overviews/windowids.h

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        windowids.h
   3 // Purpose:     topic overview
   4 // Author:      wxWidgets team
   5 // RCS-ID:      $Id$
   6 // Licence:     wxWindows licence
   7 /////////////////////////////////////////////////////////////////////////////
   8
   9 /**
  10
  11 @page overview_windowids Window IDs
  12
  13 @tableofcontents
  14
  15 Various controls and other parts of wxWidgets need an ID.  Sometimes the ID may
  16 be directly provided by the user or have a predefined value, such as
  17 @c wxID_OPEN. Often, however, the value of the ID is unimportant and is created
  18 automatically by calling wxWindow::NewControlId or by passing @c wxID_ANY as
  19 the ID of an object.
  20
  21 There are two ways to generate an ID.  One way is to start at a negative
  22 number, and for each new ID, return the next smallest number.  This is fine for
  23 systems that can use the full range of negative numbers for IDs, as this
  24 provides more than enough IDs and it would take a very very long time to run
  25 out and wrap around.  However, some systems cannot use the full range of the
  26 ID value. Windows, for example, can only use 16 bit IDs, and only has about
  27 32000 possible automatic IDs that can be generated by wxWindow::NewControlId.
  28 If the program runs long enough, depending on the program itself, using this
  29 first method would cause the IDs to wrap around into the positive ID range and
  30 cause possible clashes with any directly specified ID values.
  31
  32 The other way is to keep track of the IDs returned by wxWindow::NewControlId
  33 and don't return them again until the ID is completely free and not being used
  34 by any other objects.  This will make sure that the ID values do not clash with
  35 one another.  This is accomplished by keeping a reference count for each of the
  36 IDs that can possibly be returned by wxWindow::NewControlId. Other IDs are not
  37 reference counted.
  38
  39 @see wxIdManager, wxWindow::NewControlId(), wxWindow::UnreserveControlId()
  40
  41
  42 @section overview_windowids_type Data Types
  43
  44 A wxWindowID is just the integer type for a window ID.  It should be used
  45 almost everywhere.  To help keep track of the count for the automatically
  46 generated IDs, a new type, wxWindowIDRef exists, that can take the place of
  47 wxWindowID where needed. When an ID is first created, it is marked as reserved.
  48 When assigning it to a wxWindowIDRef, the usage count of the ID is increased,
  49 or set to 1 if it is currently reserved.  Assigning the same ID to several
  50 wxWindowIDRefs will keep track of the count. As the wxWindowIDRef gets
  51 destroyed or its value changes, it will decrease the count of the used ID. When
  52 there are no more wxWindowIDRef types with the created ID, the ID is considered
  53 free and can then be used again by wxWindow::NewControlId.
  54
  55 If a created ID is not assigned to a wxWindowIDRef, then it remains reserved
  56 until it is unreserved manually with wxWindow::UnreserveControlId. However, if
  57 it is assigned to a wxWindowIDRef, then it will be unreserved automatically and
  58 will be considered free when the count is 0, and should NOT be manually
  59 unreserved.
  60
  61 wxWindowIDRef can store both automatic IDs from wxWindow::NewControlId and
  62 normal IDs.  Reference counting is only done for the automatic IDs.  Also,
  63 wxWindowIDRef has conversion operators that allow it to be treated just like a
  64 wxWindowID.
  65
  66
  67 @section overview_windowids_using Using wxWindowIDRef
  68
  69 A wxWindowIDRef should be used in place of a wxWindowID where you want to make
  70 sure the ID is not created again by wxWindow::NewControlId at least until the
  71 wxWindowIDRef is destroyed, usually when the associated object is destroyed.
  72 This is done already for windows, menu items, and tool bar items. It should
  73 only be used in the main thread, as it is not thread safe.
  74
  75 */