UXOutlineDataSource

UXOutlineDataSource is what a UXOutlineView asks for its contents. It has four methods. Unlike a table’s data source, it addresses by item, not by row.

#use <UXKit>            // or #import "UXOutlineView.xc"

Overview

protocol UXOutlineDataSource {
    i32     numberOfChildren(UXOutlineView* o, Object* item);
    Object* childOfItem(UXOutlineView* o, Object* item, i32 i);
    bool    isExpandable(UXOutlineView* o, Object* item);
    u8*     valueForItem(UXOutlineView* o, Object* item, i32 col);
}

Why item and not row

A tree cannot address anything by row index, because a row’s meaning changes when something above it expands: row 4 is a different node before and after opening row 2. The outline hands you back the item itself.

An item is any Object* you like. The outline never inspects it; it only gives it back. Your existing model nodes work unchanged. There is no wrapper type to build and keep in sync, and no identifier to map.

`item == 0` is the root

This convention keeps every method to two lines:

i32 numberOfChildren(UXOutlineView* o, Object* item) {
    Node* n = item == (Object*)0 ? root : (Node* ?)item;
    return (i32)n.kids.count();
}

The outline asks about the root first, then walks down through whatever you return. There is no separate call for the root, because 0 means the root.

Topics

numberOfChildren · childOfItem · isExpandable · valueForItem

numberOfChildren

i32 numberOfChildren(UXOutlineView* o, Object* item)

How many children item has, or the root’s children when item is 0.

childOfItem

Object* childOfItem(UXOutlineView* o, Object* item, i32 i)

The i’th child, in display order. Sort a level here; the outline does not sort.

isExpandable

bool isExpandable(UXOutlineView* o, Object* item)

Whether this item can be opened.

This is separate from numberOfChildren. A node can be expandable before its children are known, so a lazily loaded tree can show a disclosure triangle without fetching anything first. A directory that has not been read yet answers true here and does its work in numberOfChildren when the user opens it.

For an eagerly loaded model the implementation is n.kids.count() > 0.

valueForItem

u8* valueForItem(UXOutlineView* o, Object* item, i32 col)

The text for one item in one column. Like a table’s cell, this returns text, so formatting belongs here.

item is never 0 for a real row, so a null check is only needed if your model can contain one.