- Core Foundation
You use CFTree to create tree structures that represent hierarchical organizations of information. In such structures, each tree node has exactly one parent tree (except for the root tree, which has no parent) and can have multiple children. Each CFTree object in the structure has a context associated with it; this context includes some program-defined data as well as callbacks that operate on that data. The program-defined data is often used as the basis for determining where CFTree objects fit within the structure. All CFTree objects are mutable.
You create a CFTree object using the
CFTree function. This function takes an allocator and pointer to a
CFTree structure as parameters. The
CFTree structure contains the program-defined data and callbacks needed to describe, retain, and release that data. If you do not implement these callbacks, your program-defined data will not be retained or released when trees are added and removed from a parent.
Each CFTree object has a parent and list of children, all of which may be
NULL. CFTree provides functions for adding and removing tree objects from the tree structure. Use the
CFTree functions to add trees to a tree structure, and the
CFTree functions to remove trees.
For the purposes of memory management, CFTree can be thought of as a collection. Typically the only object that retains a child tree is its parent. Usually, therefore, when you remove a child tree from a tree, the child tree is destroyed. If you want to use a child tree after you remove it from its parent, you should retain the child tree first, prior to removing it.
Releasing a tree releases its child trees, and all of their child trees (recursively). Note also that the final release of a tree (when its retain count decreases to zero) causes all of its child trees, and all of their child trees (recursively), to be destroyed, regardless of their retain counts. Releasing a child that is still in a tree is therefore a programming error, and may cause your application to crash.
You can use any of the get functions (functions containing the word “Get”) to obtain the parent, children, or attributes of a tree. For example, use
CFTree to obtain a child of a tree at a specified location. In common with other Core Foundation “Get” functions, these functions do not retain the tree that is returned. If you are making other modifications to the tree, you should either retain or make a deep copy of the child tree returned.