The contents of a TreeView object are defined by the Items property; a vector of character vectors that specifies the item labels.

The ImageListObj, ImageIndex and SelImageIndex properties define bitmapped images corresponding to each item. The bitmapped images are drawn to the left of the item labels.

ImageListObj specifies the name of a single ImageList object that contains one or more bitmaps

ImageIndex and SelImageIndex are ⎕IO sensitive scalars, or vectors with the same length as the number of items in the object. The value in the ith element specifies the image for the ith item and is an index into the corresponding ImageList object. ImageIndex specifies the image displayed when an item is not selected, SelImageIndex specifies the image displayed when an item is selected.

If ImageListObj is specified, but ImageIndex is empty or not specified, the first bitmap in the ImageList is drawn alongside every item. If an element of ImageIndex or SelImageIndex specifies a value that does not correspond to a bitmap in the ImageList, no picture is drawn.

The structure of the items (that is, the parent/child relationships of the items) is defined by the Depth property. This is either a scalar 0 (the default) which means that all items are root items, or it is a numeric vector of the same length as Items. Non-zero values in Depth indicate child items.

The HasLines property is 0, 1 or 2 and determines whether or not lines are drawn that link child items to their corresponding parent item. If HasLines is 0, no lines are drawn. If HasLines is 1, lines are drawn at all except the top level, that is, the object does not link items at the root of the hierarchy. The default value for HasLines is 2 which provides lines at all levels including the root.

The HasButtons property determines whether or not the TreeView object has a button to the left side of each parent item. It is Boolean with a default value of 1. The user can click the button to expand or collapse the child items as an alternative to double-clicking the parent item. Note that by itself, setting HasButtons to 1 does not add buttons to items at the root of the hierarchy. To achieve this you must also set HasLines to 2.

The CheckBoxes property specifies whether or not check boxes are displayed alongside items in a TreeView.

The FullRowSelect property specifies whether just the item itself, or the entire row of the TreeView, is highlighted when an item is selected. FullRowSelect should not be used if HasLines is 1 or 2

When the user presses the left mouse button over an item, the object generates an ItemDown event. This is followed by an ItemUp event when the mouse button is released. The object also generates an ItemDblClick event when the left mouse is double-clicked over an item. If all three events are enabled, they are reported in the order ItemDown, ItemDblClick, ItemUp.

When a parent item is in its retracted state (its children are not visible) it can be expanded to show its children by the user double-clicking its label or by clicking over its button or tree lines. An Expanding event is reported immediately before the children are shown. Similarly, when a parent item is in its expanded state, it can be retracted to hide its children when a Retracting event is reported. You can use the Expanding event to define new children for the object just before they are shown. You can also control the actions of these events using callback functions.

The EditLabels is a Boolean property (default 0) that determines whether or not the user may edit the labels which are specified by the Items property.

The SelItems property is a Boolean vector that indicates which of the items is currently selected and has the focus. If more items are visible than can fit within the object, a scrollbar is automatically provided. The Index property is a ⎕IO sensitive integer that reports the index number of the first item displayed in the object and changes as the items are scrolled.

Warning: Due to the limitations of the Win32 TreeView object, it is necessary to query the state of each item in a TreeView in order to obtain the value of the SelItems property, making it a comparatively slow operation if there are a lot of Items.