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Tree - Demos


A Tree represents a hierarchical list of items that might have child items that can be expanded, collapsed, or selected. To create a Tree within react-md, the basic requirements are to provide:

  • an id for the tree (required for a11y)
  • either an aria-label or aria-labelledby describing the purpose of the tree
  • an object of TreeData to render where the requirements are to have an itemId and parentId referencing other itemIds within the tree or null for root level items.
  • a list of selected itemIds within the tree and handlers for updating the selected ids
  • a list of expanded itemIds within the tree and handlers for updating the expanded ids

This might seem like a lot to get started with, but luckily @react-md/tree provides two hooks for handling the selectedIds and expandedIds named useTreeItemSelection and useTreeItemExpansion that should work for most cases out of the box.

A tree will be created by traversing the TreeData and linking itemIds of each item to a parentId. Every item that has a parentId pointing to null (or a custom rootId prop) will appear at the root of the tree while all parentIds pointing to another itemId will be a child of that item.

If you are a Typescript user, this package also provides a bunch of types you can use to strictly type your tree: TreeItemIds, BaseTreeItem, TreeData, TreeItemSorter, TreeItemRenderer, etc. See more in the examples below.

# Built-in Accessibility

One of the biggest "selling points" for this package is the built-in accessibility and keyboard movement. They key features are:

  • accessible keyboard movement using aria-activedescendant
  • moving up and down the tree with ArrowUp and ArrowDown keys
  • selecting and clicking items with Space and Enter
  • jumping to the first or last item in the tree with Home and End
  • typeahead to match visible tree items with the same letters that were typed
  • expanding and collapsing tree items with the ArrowRight and ArrowLeft keys
    • jumping to a parent tree item with the ArrowLeft
    • jumping to the first child of an expanded tree item with ArrowRight
  • expanding all tree items at the current level with * (asterisk)
  • selecting all visible items in the tree with Control+a (requires multiSelect prop enabled)
  • selecting all visible tree items from the current selection to the first tree item with Control+Shift+Home (requires multiSelect prop enabled)
  • selecting all visible tree items from the current selection to the last tree item with Control+Shift+End (requires multiSelect prop enabled)

#Single Select Tree

One of the most common forms of a tree is a single selection tree that only allows one item to be selected at a time. This example will render a very simple folder tree and show how items are linked together and rendered within the tree along with an example of using the useTreeItemSelection and useTreeItemExpansion hooks.

The useTreeItemSelection hook returns an object containing the following props to pass to the Tree component to get selection behavior:

  • selectedIds - A list of the current selected ids within the tree.
  • onItemSelection - A callback that updates the selectedIds when an item within the tree is clicked
  • onMultiItemSelection - A callback that updates the selectedIds when a "batch selection" occurs. This callback will never be called if the second argument for this hook is omitted or set to false.
  • multiSelect - Boolean if multi-select behavior is enabled for this tree. The default is false.

The useTreeItemExpansion hook returns an object containing the following props to pass to the Treecomponent to get expansion behavior:

  • expandedIds - A list of the current expanded ids within the tree.
  • onItemExpansion - A callback that updates the expandedIds when a tree item should be expanded or collapsed
  • onMultiItemExpansion - A callback that updates the expandedIds when a "batch expansion" occurs (pressing the asterisk * key)
  • Folder 1
  • Folder 3

#Multi Select Tree

To create a multi-selectable tree, all that is required is to enable the multiSelect argument on the useTreeItemSelection hook. Now multi tree items will be selectable and the additional keyboard shortcuts for selecting items will be enabled.

  • Folder 1
  • Folder 3

#Customizing Tree Items

Now that you've learned a bit about how to use the Tree component to render simple trees, let's look at how we can customize how each item is rendered with the getItemProps prop on the Tree.

This prop can be used to add additional styling or general ListItem props that you'd like to not store in your tree and dynamically apply to each item. This function will provide the current item merged with the focused, selected, and expanded booleans representing the state of the item.

The example below will render a simple "code file tree" by dynamically applying icons based on file types and overriding some styles when focused or selected.

  • public
    • robots.txt
  • src
    • index.html
    • Demo.tsx
    • _variables.scss
    • index.ts