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shockwave 预载技术（2）
shockwave 预载技术
原著：lingoworkshop
翻译：alphachi
为了让程序拥有更强的适应性，我们还可以添加一.netdone()命令用来检测网络错误。“preloader”剧本的下一个版本能够检测任何网络错误。一旦发生错误，则使用一个参数返回错误的描述信息；如果没有错误，那么此参数的取值为一个空字符串。
"preloader" parent script (v.3)
property m.netid, mycallbackobj, mycompletionmsg
on new ( me ,.netaddress, callbackobj, completionmsg)
mycallbackobj = callbackobj
mycompletionmsg = completionmsg
m.netid = preloa.netthing .netaddress)
atimerobj = timeout ( me . string ). new ( 100 , # timer_checkprogress, me )
end
on timer_checkprogress ( me , atimer)
finished =.netdone (m.netid)
if finished then
errornotification = ""
errornum =.neterror (m.netid)
if integerp (errornum) then
if errornum then
errornotification = me ._geterror(errornum)
end if
end if
atimer. forget ()
call (mycompletionmsg, mycallbackobj, errornotification)
else
put "still downloading"
end if
end
on _geterror ( me , errorcode)
case errorcode of
"ok" , "" , 0: return empty
4: errormsg =( "bad moa class. the required xtras are missing. " )
5: errormsg =( "the required xtras are improperly installed or not installed at all." )
6: errormsg =( "bad url or the required xtras are improperly installed. " )
20: errormsg =( "internal error. the browser detected a.network or internal error." )
4146: errormsg =( "connection could not be established with the remote host." )
4149: errormsg =( "data supplied by the server was in an unexpected format." )
4150: errormsg =( "unexpected early closing of connection." )
4154: errormsg =( "operation could not be completed due to timeout." )
4155: errormsg =( "not enough memory available to complete the transaction." )
4156: errormsg =( "protocol reply to request indicates an error in the reply." )
4157: errormsg =( "transaction failed to be authenticated." )
4159: errormsg =( "invalid url." )
4164: errormsg =( "could not create a socket." )
4165: errormsg =( "requested object could not be found (url may be incorrect)." )
4166: errormsg =( "generic proxy failure." )
4167: errormsg =( "transfer was intentionally interrupted by client." )
4242: errormsg =( "download stopped by.netabort(url)." )
4836: errormsg =( "download stopped for an unknown reason, possibly a.network error, or the download was abandoned." )
otherwise
errormsg =( "unknown error code" )
end case
return errormsg
end
要想看到具体返回了什么参数，可以像下面这样修改“preloaderinterface”行为：
on beginsprite me
clearcache ()
urltoload = "http://www.lingoworkshop.com/tutorials/preloader/main.dcr"
script ( "preloader" ). new (urltoload, me , # mhandlepreloadcompletion)
end
on mhandlepreloadcompletion ( me , errormsg)
if errormsg <> empty then alert .network error!" & return & errormsg
else alert "all done"
end
现在，”preloader”剧本已经有能力预载一个url并在预载完成时对另一个对象进行返回调用。最后一步则是让“preloader”剧本可以报告其运行状态，以便我们制作一个进度条来给用户提供一些反馈信息。为了达到这一目的，我们可以使用getstreamstatus(m.netid)函数获取网络操作的当前状态。这个函数会返回一个属性列表，其中包含像#state（可能是“connecting”或“in progress”）、字节总数和当前已传递字节数这样的信息。在“preloader”剧本的最终版本中，这些信息被用来确定url已被下载的部分。此版本附加了一个起始参数“statusmsg”——返回调用目标用于显示当前网络状况的程序名称。
"preloader" parent script (v.4)
property m.netid, mycallbackobj, mycompletionmsg, mystatusmessage
on new ( me ,.netaddress, callbackobj, completionmsg, statusmsg)
mycallbackobj = callbackobj
mycompletionmsg = completionmsg
mystatusmessage = statusmsg
m.netid = preloa.netthing .netaddress)
atimerobj = timeout ( me . string ). new ( 100 , # timer_checkprogress, me )
end
on timer_checkprogress ( me , atimer)
finished =.netdone (m.netid)
if finished then
errornotification = ""
errornum =.neterror (m.netid)
if integerp (errornum) then
if errornum then
errornotification = me ._geterror(errornum)
end if
end if
atimer. forget ()
call (mycompletionmsg, mycallbackobj, errornotification)
else
-- 仍在预载；检测是否需要报告当前状态
if mystatusmessage. ilk = #symbol then
-- 已经得到一个返回调用消息；获取状态列表并将其发送给返回调用目标
thestatus = getstreamstatus (m.netid)
currentstate = thestatus. state
-- 在发送状态列表前计算出已下载部分（变量“fractiondone”）
case (currentstate) of
"inprogress" :
if thestatus.bytessofar > 0 then
if thestatus.bytestotal > 0 then fractiondone = min ( 1 . 0 , float (thestatus.bytessofar) / thestatus.bytestotal )
else fractiondone = 50
else
fractiondone = 0
end if
"complete" :
fractiondone = 100
otherwise
fractiondone = 0
end case
-- 将fractiondone作为一个属性添加到状态列表中
thestatus. addprop ( # fractiondone, fractiondone )
-- 通知当前状态的返回调用对象和已传递的百分比
call (mystatusmessage, [mycallbackobj], thestatus)
end if
end if
end
on _geterror ( me , errorcode)
case errorcode of
"ok" , "" , 0: return empty
4: errormsg =( "bad moa class. the required xtras are missing. " )
5: errormsg =( "the required xtras are improperly installed or not installed at all." )
6: errormsg =( "bad url or the required xtras are improperly installed. " )
20: errormsg =( "internal error. the browser detected a.network or internal error." )
4146: errormsg =( "connection could not be established with the remote host." )
4149: errormsg =( "data supplied by the server was in an unexpected format." )
4150: errormsg =( "unexpected early closing of connection." )
4154: errormsg =( "operation could not be completed due to timeout." )
4155: errormsg =( "not enough memory available to complete the transaction." )
4156: errormsg =( "protocol reply to request indicates an error in the reply." )
4157: errormsg =( "transaction failed to be authenticated." )
4159: errormsg =( "invalid url." )
4164: errormsg =( "could not create a socket." )
4165: errormsg =( "requested object could not be found (url may be incorrect)." )
4166: errormsg =( "generic proxy failure." )
4167: errormsg =( "transfer was intentionally interrupted by client." )
4242: errormsg =( "download stopped by.netabort(url)." )
4836: errormsg =( "download stopped for an unknown reason, possibly a.network error, or the download was
abandoned.")
otherwise
errormsg =( "unknown error code" )
end case
return errormsg
end
