@c    GNUstep AppKit Guide
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@c    Copyright (c)  2005-2006  Christopher Armstrong.
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@node outlineviews, matrix, tableview, Top
@chapter Outline Views

An @dfn{outline view} is a specialised form of table view designed for displaying hierachical data in a tree like format. It looks alot like a Windows' TreeView Control, but operates differently, provides much more powerful functionality and it is less tedious to programme.

The node's in the outline view can be collapsed and expanded and display a list of sub-nodes. This makes the outline view hierachical.

It uses the @code{NSOutlineView} class, which inherits from @code{NSTableView}. This means that most of the behaviour that applies to tableviews also applies to outline views, such as changing columns/rows and their display, etc. It extends the tableview with a hierachial layout for data, in which nodes can be expanded and contracted.

Like the table view, the outline view control uses a data source object to get it's data, as well as a delegate to modify it's behaviour. These are objects implementing the informal protocols @code{NSOutlineViewDataSource} and @code{NSOutlineViewDelegate}. Although a delegate object is optional, outline views require a data source object.

See the @cite{GNUstep GUI Reference} for more information about outline views (including class documentation).

@section Using a Data Source

The data source for an outline view implements the @code{NSOutlineViewDataSource} informal protocol. Some of it's methods are compulsory; some are not.

Note that a parameter in many of the delegate's methods is an untyped object @var{item}. This object is supplied by you, and the outline view passes it back to your delegate as a representation of a node or leaf row.

The outline view requires you implement the following methods:
@table @code
@item -(id) outlineView:(NSOutlineView*)outlineView child:(int)index ofItem:(id)item
Returns the item that is the child of @var{item} at @var{index}. A @code{nil} item means that you should return the children of the root item.

@item -(BOOL) outlineView:(NSOutlineView*)outlineView isItemExpandable:(id)item
Returns whether @var{item} is expandable.

@item -(int) outlineView:(NSOutlineView*)outlineView numberOfChildrenOfItem:(id)item
Returns the number of child items of @var{item}.

@item -(id) outlineView:(NSOutlineView*)outlineView objectValueForTableColumn: (NSTableColumn*)tableColumn byItem:(id)item
Returns the data object for @var{item} in @var{tableColumn} of the table view.
@end table

Full defintions of these (and optional methods) can be found in the @cite{GNUstep GUI Manual}.