分析Lua观察者模式最佳实践之构建事件分发系统

local B = class()
function B:on_money_change( money )
    print(money, "B receive event")
end
-- 订阅金币修改事件
EventSystem:on(Event.MoneyChanged, B.on_money_change, {target = B})

local C = class()
function C:on_money_change( money )
    print(money, "C receive event")
end
EventSystem:on(Event.MoneyChanged, C.on_money_change, {target = C})
-- 在A模块中派发金币修改事件，当前金币为10
EventSystem:emit(Event.MoneyChanged, 10)

function EventSystem:on( event, func, params )
    --- ...
    local event_listener = self._listeners[event]
    params = params or {}
    local priority = params.priority or 0
    local target = params.target
    --- ...
    local cb = {target = target, func = func, id = id, priority = priority}
    table.insert(event_listener.list, cb)
    id = id + 1
    if priority > 0 then
        event_listener.need_sort = true
        self:sort(event_listener)
    end
end

function EventSystem:sort( listener )
    if listener.need_sort == true and listener.emit_count == 0 then
        table.sort(listener.list, function ( a, b )
            if a.priority == b.priority then
                return a.id < b.id
            else
                return a.priority > b.priority
            end
        end)
        listener.need_sort = false;
    end
end

function EventSystem:off( event, func, params )
    --- ...
    local event_listener = self._listeners[event]
    params = params or {}
    for i,cb in ipairs(event_listener.list) do
        if cb.func == func and cb.target == params.target then
            if event_listener.emit_count > 0 then
                -- 派发过程中只进行标记删除
                cb.need_remove = true
                event_listener.need_clean = true
            else
                table.remove(event_listener.list, i)
            end
            break;
        end
    end
end

function EventSystem:emit( event, ... )
    --- ...
    local event_listener = self._listeners[event]
    local interrupt = false
    local length = #event_listener.list
    -- 这里不能使用ipairs，确保不会触发在派发过程中注册的事件
    -- 只取当前已经注册的事件数量，如果在派发过程中再注册（调用了table.insert），本次派发也不会调用
    for i = 1, length do
        if interrupt == true then
            break
        end
        local cb = event_listener.list[i]
        if cb.func and cb.need_remove ~= true then
            event_listener.emit_count = event_listener.emit_count + 1
            if cb.target then
                interrupt = cb.func(cb.target, ...)
            else
                interrupt = cb.func(...)
            end
            event_listener.emit_count = event_listener.emit_count - 1
        end
    end
    self:sort(event_listener);
    self:clean(event_listener);
    return interrupt
end