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The Asset Browser's catalog UI is created using the tree-view API.

Available via:

#include "UI_tree_view.hh"

This kind of view is made for showing data that is hierarchical. Items support:

  • Custom layouts
  • Renaming
  • Activating
  • Custom drag & drop controllers
  • Custom context menus
  • Collapsing parent items

Building tree UIs becomes much simpler as the UI code does a lot of the heavy lifting. The tree is built by first defining a number of items and child items, then each visible item is built into a row layout.

Creating a Tree-View

Defining a new tree can be done as simple as this:

class MyTreeView : public ui::AbstractTreeView {
  void build_tree() override
    ui::BasicTreeViewItem& item = add_tree_item<ui::BasicTreeViewItem>(IFACE_("Some Item"), ICON_HOME);
    /* Child item. */
    item.add_tree_item<ui::BasicTreeViewItem>(IFACE_("Child Item"), ICON_CON_CHILDOF);

    add_tree_item<ui::BasicTreeViewItem>(IFACE_("Item without icon"));

Each item added to the tree will be displayed as a row (if it is visible), nested under its parent. Parent items are collapsible. In the example above, the items are of type ui::BasicTreeViewItem, which is a predefined item type for simple tree rows. Each row only contains an icon and a label.
For more control over what goes into a row, custom item types can be defined in a similar fashion:

class MyTreeViewItem : public ui::AbstractTreeViewItem {
  void build_row(uiLayout& row) override
    /* ... Regular UI layout code ... */

Different item types can be mixed in a tree.

Lastly, the actual instance of the tree-view can be created for a uiBlock:

ui::AbstractTreeView *tree_view = UI_block_add_view(
    "My tree View",

ui::TreeViewBuilder builder(*block);

For a more complex real-life example, check the asset catalog tree-view code:

Design Notes

  • Every row has a tree-row button (UI_BTYPE_TREEROW). An overlapping layout is used to place it underneath the customizable row layout of each item.


BasicTreeViewItem: Custom Activation Behavior

To not have to create a sub-class of ui::BasicTreeViewItem just to customize its activation behavior, it offers a different way to set the custom behavior:

ui::BasicTreeViewItem& item = add_tree_item<ui::BasicTreeViewItem>(IFACE_("All"), ICON_HOME);

/* Pass activation behavior as lambda, function object or plain old function pointer. */
item.on_activate([](ui::BasicTreeViewItem &item) {
  std::cout << "I've been activated!" << std::endl;


For general view system To-Do's, see T98560.

  • Support reordering or changing the hierarchy via drag & drop (the generic parts of it, like finding and visualizing the item to insert into/before/after, drop polls, reinsert callbacks, etc.)
  • Avoid \(O(n^2)\) complexity of state reconstruction, more precisely AbstractTreeView::update_children_from_old_recursive().
  • Draw hierarchy lines.