docs/doxygen/overviews/windowids.h

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