【界面UI】下拉列表：服务器选择的分组渲染

---下拉列表：分组标题与选项的渲染
function Dropdown.show(win, groups)
    local list = GUI:ListView_Create(win, "opts", 0, 0, 200, 240)
    Dropdown.rows = {}
    for _, g in ipairs(groups) do
        -- 分组标题：置灰不可点
        local head = GUI:Text_Create(list, "g_" .. g.name,
            0, 0, 11, "#999999", "— " .. g.name .. " —")
        head.selectable = false
        for _, s in ipairs(g.servers) do
            local row = GUI:Text_Create(list, "s_" .. s.id,
                0, 0, 12, "#FFFFFF", s.name)
            GUI:addOnClickEvent(row, function()
                Dropdown.pick(s)
            end)
            Dropdown.rows[#Dropdown.rows + 1] = row
        end
    end
end

---选中态的管理：唯一高亮与回调
function Dropdown.pick(server)
    if Dropdown.selected then
        Dropdown.selected.color = "#FFFFFF"
    end
    Dropdown.selected = server
    Dropdown.selectedRow.color = "#FFD700"
    Dropdown.onPicked(server)
    Dropdown.collapse()
end

---推荐分组的置顶：负载均衡的引导
function Dropdown.sort(groups)
    -- 推荐的服务器置顶：负载低且有新手加成
    table.sort(groups[1].servers, function(a, b)
        return a.load < b.load
    end)
end