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| __NOTOC__
| | {{ Moved To Community | KDE_Visual_Design_Group/HIG/TreeView }} |
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| == Tree View ==
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| With a ''tree view'' users can view and interact with a hierarchically arranged collection of objects, using either single selection or multiple selections. In a tree, objects that contain data are called ''leaf nodes'' and objects that contain other objects are called ''container nodes''. A single, top-most container node is called the ''root node''.
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| [[File:TreeView.png]]
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| A tree view is the appropriate control for items that have a single, natural, hierarchical categorization that's familiar to most users with more than two levels (not including the root node). But having hierarchical data doesn't mean a tree view must be used. Very often a list view or a combination of list view and drop-down list is a simpler, yet more powerful choice. The disadvantage of a tree view is that users may not completely understand the layout of the tree, but they will form a mental model of the relationships after interacting with the tree for a while. If that mental model is incorrect, it leads to confusion. The challenge when designing a tree is to balance discoverability with a predictable user model that minimizes confusion.
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| == Guidelines ==
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| === Is this the right control ===
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| * Apply a tree view to large data sets that can be categorized with more than two levels.
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| * Ideally, a tree should have no more than four levels (not counting the root node) and the most commonly accessed objects should appear in the first two levels.
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| * Use a natural hierarchical structure that's familiar to most users. Balance discoverability with a predictable user model that minimizes confusion.
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| * Consider to break down the hierarchical data, for instance into a selection by a [[Projects/Usability/HIG/DropDown | drop-down list]] with an associated [[Projects/Usability/HIG/ListView | list view]].
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| === Behavior ===
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| * Start item’s default behavior with double click. Make double-click behavior redundant via button or context menu.
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| * Provide navigation by keys per directional arrows, plus Home, End, Page Up, and Page Down.
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| * Provide a context menu with relevant commands.
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| * Provide a root node only if users need the ability to perform commands on the entire tree.
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| * Users should always be able to expand and collapse container nodes by clicking the expander buttons.
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| * Apply a header with meaningful caption to columns.
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| * Avoid presenting empty trees.
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| * If the tree has alternative access methods such as a word search or an index, optimize the tree for browsing by focusing on the most useful content.
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| : Multi selection:
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| * Use check boxes to indicate the option for multiple selections.
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| * For check boxes, use the mixed state to indicate that an option is set for some, but not all, child objects. Users should not be able to set a mixed state directly (cf. [[Projects/Usability/HIG/Check_Box|check boxes]]).
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| * Clicking a mixed state check box selects all child objects and the parent check box.
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| * Don’t use check boxes in single selection trees.
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| === Appearance ===
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| * If high-level containers have similar contents, consider using visual clues, e.g. icons to differentiate them.
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| * If users expand or collapse a container, make that state persist so it takes effect the next time the tree view is displayed, unless users are likely to prefer starting in the default state.
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| * Make the the control large enough that it can show at least eight items at a time without scrolling.
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| * Label the tree view with a descriptive caption to the top left (cf. [[Projects/Usability/HIG/Alignment | alignment]]).
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| * Create a buddy relation so access keys are assigned.
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| * Do not use ending punctuation (neither dot nor colon) for caption.
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| * Use sentence [[Projects/Usability/HIG/Capitalization | style capitalization]] for tree view items.
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| == Implementation ==
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| [[Category:Usability]][[Category:Behavior]][[Category:Viewing_and_Navigation]][[Category:Complex_views]]
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