界面中介：面板与数据的职责分离

-- 错误：面板与数据互相直呼，缠死
function onDataChange(data)
    bagPanel:refresh(data)
    mailPanel:refresh(data)
end

local mediators = {}
local function register(name, m)
    mediators[name] = m
end
local function notify(name, event, data)
    local m = mediators[name]
    if m ~= nil then
        m:onEvent(event, data)
    end
end