【性能调优】列表控件的虚拟化：千条邮件的流畅滚动

-- 只创建可视区数量 + 2 的控件池
local visibleCount = 12
local cellPool = {}
function MailList.init(list, dataSource)
    for i = 1, visibleCount + 2 do
        cellPool[i] = createCellWidget(list)
    end
    list.dataSource = dataSource
    list.offset = 0
end

function MailList.onScroll(list, offset)
    local first = math.floor(offset / CELL_HEIGHT)
    for i, cell in ipairs(cellPool) do
        local dataIndex = first + i - 1
        local mail = list.dataSource[dataIndex]
        if mail then
            refreshCell(cell, mail)
            cell:setVisible(true)
        else
            cell:setVisible(false)
        end
    end
end