Development guidelines

TreeGrid, TreeGridRow, and TreeGridCell are components used to create a tree hierarchy. They’re not visually styled components, but instead help with adding keyboard navigation and roving tabindex behaviors to tree grid structures.

A tree grid is a hierarchical 2 dimensional UI component, for example it could be used to implement a file system browser.

A tree grid allows the user to navigate using arrow keys. Up/down to navigate vertically across rows, and left/right to navigate horizontally between focusables in a row.

For more information on a tree grid, see the following links:

• https://www.w3.org/TR/wai-aria-practices/examples/treegrid/treegrid-1.html

Usage

The TreeGrid renders both a table and tbody element, and is intended to be used with TreeGridRow (tr) and TreeGridCell (td) to build out a grid.

function TreeMenu() {
    return (
        <TreeGrid>
            <TreeGridRow level={ 1 } positionInSet={ 1 } setSize={ 2 }>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onSelect } { ...props }>Select</Button>
                    ) }
                </TreeGridCell>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onMove } { ...props }>Move</Button>
                    ) }
                </TreeGridCell>
            </TreeGridRow>
            <TreeGridRow level={ 1 } positionInSet={ 2 } setSize={ 2 }>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onSelect } { ...props }>Select</Button>
                    ) }
                </TreeGridCell>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onMove } { ...props }>Move</Button>
                    ) }
                </TreeGridCell>
            </TreeGridRow>
            <TreeGridRow level={ 2 } positionInSet={ 1 } setSize={ 1 }>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onSelect } { ...props }>Select</Button>
                    ) }
                </TreeGridCell>
                <TreeGridCell>
                    { ( props ) => (
                        <Button onClick={ onMove } { ...props }>Move</Button>
                    ) }
                </TreeGridCell>
            </TreeGridRow>
        </TreeGrid>
    );
}

Sub-Components

TreeGrid

Props

Aside from the documented callback functions, any props specified will be passed to the table element rendered by TreeGrid.

TreeGrid should always have children.

onFocusRow: ( event: KeyboardEvent, startRow: HTMLElement, destinationRow: HTMLElement ) => void

Callback that fires when focus is shifted from one row to another via the Up and Down keys. Callback is also fired on Home and End keys which move focus from the beginning row to the end row.
The callback is passed the event, the start row element that the focus was on originally, and
the destination row element after the focus has moved.

• Required: No

onCollapseRow: ( row: HTMLElement ) => void

A callback that passes in the row element to be collapsed.

• Required: No

onExpandRow: ( row: HTMLElement ) => void

A callback that passes in the row element to be expanded.

• Required: No

TreeGridRow

Props

Additional props other than those specified below will be passed to the tr element rendered by TreeGridRow, so for example, it is possible to also set a className on a row.

level: number

An integer value designating the level in the hierarchical tree structure. Counting starts at 1. A value of 1 indicates the root level of the structure.

• Required: Yes

positionInSet: number

An integer value that represents the position in the set. A set is the count of elements at a specific level. Counting starts at 1.

• Required: Yes

setSize: number

An integer value that represents the total number of items in the set, at this specific level of the hierarchy.

• Required: Yes

isExpanded: boolean

An optional value that designates whether a row is expanded or collapsed. Currently this value only sets the correct aria-expanded property on a row, it has no other built-in behavior.

If there is a need to implement aria-expanded elsewhere in the row, cell, or element within a cell, you may pass isExpanded={ undefined }. In order for keyboard navigation to continue working, add the data-expanded attribute with either true/false. This allows the TreeGrid component to still manage keyboard interactions while allowing the aria-expanded attribute to be placed elsewhere. See the example below.

• Required: No

function TreeMenu() {
    return (
        <TreeGrid>
            <TreeGridRow level={ 1 } positionInSet={ 1 } setSize={ 2 } isExpanded={ undefined } data-expanded={ false }>
                <TreeGridCell>
                    { ( props ) => (
                        <Button aria-expanded="false" onClick={ onSelect } { ...props }>Select</Button>
                    ) }
                </TreeGridCell>
            </TreeGridRow>
        </TreeGrid>
    );
}

TreeGridCell

Props

TreeGridCell accepts no specific props. Any props specified will be passed to the td element rendered by TreeGridCell.

children as a function

TreeGridCell renders children using a function:

<TreeGridCell>
    { ( props ) => (
        <Button onClick={ doSomething } { ...props }>
            Do something
        </Button>
    ) }
</TreeGridCell>

Props passed as an argument to the render prop must be passed to the child focusable component/element within the cell. If a component is used, it must correctly handle the onFocus, tabIndex, and ref props, passing these to the element it renders. These props are used to handle the roving tabindex functionality of the tree grid.

Related components

• This component implements RovingTabIndex.