5e6ce06a0d
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51254 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
64 lines
3.8 KiB
TeX
64 lines
3.8 KiB
TeX
\section{Window IDs overview}\label{windowidsoverview}
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\wxheading{See Also}
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\helpref{wxIdManager}{wxidmanager}
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\helpref{wxWindow::NewControlId}{wxwindownewcontrolid}
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\helpref{wxWindow::UnreserveControlId}{wxwindowunreservecontrolid}
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\subsection{Introduction}\label{windowidsoverviewintro}
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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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\texttt{wxID\_OPEN}. Often, however, the value of the ID is unimportant and is
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created automatically by calling \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}
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or by passing \texttt{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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more than enough IDs and it would take a very very long time to run out and
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wrap around. However, some systems can not use the full range of the ID value.
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Windows, for example, can only use 16 bit IDs, and only has about 32000 possible
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automatic IDs that can be generated by \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}.
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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 \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}
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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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another. This is accomplished by keeping a reference count for each of the IDs
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that can possibly be returned by \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}.
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Other IDs are not reference counted.
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\subsection{Data types}\label{windowidsoverviewtypes}
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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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a new type, wxWindowIDRef exists, that can take the place of wxWindowID where needed.
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When an ID is first created, it is marked as reserved. When assigning it to a
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wxWindowIDRef, the usage count of the ID is increased, or set to 1 if it is currently
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reserved. Assigning the same ID to several wxWindowIDRefs will keep track of the count.
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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 \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}.
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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 \helpref{wxWindow::UnreserveControlId}{wxwindowunreservecontrolid}.
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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 \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}
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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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\subsection{Using wxWindowIDRef}\label{windowidsoverviewusing}
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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 \helpref{wxWindow::NewControlId}{wxwindownewcontrolid}
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at least until the 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.
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It should only be used in the main thread, as it is not thread safe.
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