DaVinci Resolve UIManager.Tree with checkBoxes

Tree With CheckBoxes.lua

--Licensed under CC0 1.0 https://creativecommons.org/publicdomain/zero/1.0/
--Add this file to C:\ProgramData\Blackmagic Design\DaVinci Resolve\Fusion\Scripts\Comp
--tree:SetItemWidget is no available unfortunatelly, which means we cannot add custom widgets to TreeItems.
--So we have to use this method. (only checkBoxes are supported)

local ui = fu.UIManager
local disp = bmd.UIDispatcher(ui)

-- create a new window
local win = disp:AddWindow({
    ID = "Dialog",
    WindowTitle = "Generate Comp",
    ui:Tree {
        ID = "Tree",
        RootIsDecorated = false,
        Events = { CurrentItemChanged = true, ItemChanged = true, },
    }
})
local winItems = win:GetItems()
local tree = winItems.Tree

-- for performance ?
tree.SortingEnabled = false
tree.UpdatesEnabled = false

-- add TreeItems to the Tree
for i = 1, 50 do
    local treeItem = tree:NewItem() -- to create TreeItem, we need to call NewItem(). (ui.TreeItem is nil)
    treeItem.Text[0] = "Item " .. i
    treeItem.CheckState[0] = "Checked" -- without this, the checkbox is not shown. 
    -- Make sure it is .CheckState[i] = "Checked" (or "UnChecked"), not .CheckState = "Checked" (or "UnChecked").
    -- It took me many hours to figure out this bug...
    treeItem.Flags = {
        ItemIsSelectable = true,
        ItemIsEnabled = true,
        ItemIsUserCheckable = true, -- without this, the checkbox cannot be edited
    }
    treeItem:SetData(0, "UserRole", tostring(i)) -- without this, the events will not be triggered
    tree:AddTopLevelItem(treeItem) -- add the TreeItem to the Tree
end

-- for performance ?
tree.SortingEnabled = true
tree.UpdatesEnabled = true

-- print message when the checkboxes are clicked
function win.On.Tree.ItemChanged(ev)
    if ev.item then
        local id = ev.item:GetData(0, "UserRole")
        print("Item " .. id .. " " .. ev.item.CheckState[0])
    end
end

-- close the window
function win.On.Dialog.Close(ev)
    disp:ExitLoop()
end

-- show the window
win:Show()
disp:RunLoop()
win:Hide()