# Tree Widget

    Application Header file	<X11/Xaw/Tree.h>
    Class Header file	<X11/Xaw/TreeP.h>
    Class		treeWidgetClass
    Class Name	Tree
    Superclass	Constraint

The Tree widget provides geometry management of arbitrary widgets arranged in a directed, acyclic graph (i.e., a tree). The hierarchy is constructed by attaching a constraint resource called `treeParent` to each widget indicating which other node in the tree should be treated as the widget's superior. The structure of the tree is shown by laying out the nodes in the standard format for tree diagrams with lines drawn connecting each node with its children.

The Tree sizes itself according to the needs of its children and is not intended to be resized by its parent. Instead, it should be placed inside another composite widget (such as the `Porthole` or `Viewport`) that can be used to scroll around in the tree.

## Resources

When creating a Tree widget instance, the following resources are retrieved from the argument list or from the resource database:

Name | Class | Type | Notes | Default Value
accelerators | Accelerators | AcceleratorTable |  | NULL
ancestorSensitive | AncestorSensitive | Boolean | D | True
autoReconfigure | AutoReconfigure | Boolean |  | False
background | Background | Pixel |  | XtDefaultBackground
backgroundPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderColor | BorderColor | Pixel |  | XtDefaultForeground
borderPixmap | Pixmap | Pixmap |  | XtUnspecifiedPixmap
borderWidth | BorderWidth | Dimension |  | 1
children | ReadOnly | WidgetList | R | NULL
colormap | Colormap | Colormap |  | Parent's Colormap
depth | Depth | int | C | Parent's Depth
destroyCallback | Callback | XtCallbackList |  | NULL
foreground | Foreground | Pixel |  | XtDefaultForeground
gravity | Gravity | XtGravity |  | WestGravity
height | Height | Dimension | A | see Tree::Layout_Semantics
hSpace | HSpace | Dimension |  | 4
lineWidth | LineWidth | Dimension |  | 0
mappedWhenManaged | MappedWhenManaged | Boolean |  | True
numChildren | ReadOnly | Cardinal | R | 0
screen | Screen | Screen | R | Parent's Screen
sensitive | Sensitive | Boolean |  | True
vSpace | VSpace | Dimension |  | 4
translations | Translations | TranslationTable |  | NULL
width | Width | Dimension | A | see Tree::Layout_Semantics
x | Position | Position |  | 0
y | Position | Position |  | 0

`autoReconfigure`

- Whether or not to layout the tree every time a node is added or removed.

`gravity`

- Specifies the side of the widget from which the tree should grow. Valid values include `WestGravity`, `NorthGravity`, `EastGravity`, and `SouthGravity`.

`hSpace`

`vSpace`

- The amount of space, in pixels, to leave between the children. This resource specifies the amount of space left between the outermost children and the edge of the box.

`lineWidth`

- The width of the lines from nodes that do not have a `treeGC` constraint resource to their children.

## Constraint Resources

Each child of the Tree widget must specify its superior node in the tree. In addition, it may specify a GC to use when drawing a line between it and its inferior nodes.

Name | Class | Type | Notes | Default Value
treeGC | TreeGC | GC |  | NULL
treeParent | TreeParent | Widget |  | NULL

`treeGC`

- This specifies the GC to use when drawing lines between this widget and its inferiors in the tree. If this resource is not specified, the Tree's `foreground` and `lineWidth` will be used.

`treeParent`

- This specifies the superior node in the tree for this widget. The default is for the node to have no superior (and to therefore be at the top of the tree).

## Layout Semantics

Each time a child is managed or unmanaged, the Tree widget will attempt to reposition the remaining children to fix the shape of the tree if the resource is set. Children at the top (most superior) of the tree are drawn at the side specified by the resource.

After positioning all children, the Tree widget attempts to shrink its own size to the minimum dimensions required for the layout.

## Convenience Routines

The most efficient way to layout a tree is to set `autoReconfigure` to False and then use the XawTreeForceLayout routine to arrange the children.

      void XawTreeForceLayout
      Widget w

w

- Specifies the Tree widget.