Anthony
Sat Oct 13 08:06:01 PDT 2007
"Peter" <Peter@discussions.microsoft.com> wrote in message
news:28EE3263-F6C1-440B-A52D-92157CB2CC11@microsoft.com...
> Thanks Jan for the answer.
> The goal was to build the drop down list with all 2800 Cities and their
> postcode in it so the user can select the city rather then typing it.
> Problem is that it takes a huge time to download this content from the
server
> (SQL data) to the client. It would goes faster if this data was locally
> stored since she would not change in the future. (unless the spilt of HBV
> will cause Flemish cities become Brussels cities, according to the current
> political crisis in Belgium)
>
To boil the issue down you have a large amount of data that you want to
transfer to the client and store it locally so that its not retrieved every
time the page is hit by that client.
This is what the local browser cache is for.
Place the postcodes and cities in an XML file (lets call it cities.xml)
In IIS manager add a Cache-Control header to the file with the value
"max-age: 900" A 15 minute life time may seem too conservative but its not
since all it really means is how often a round trip resulting in a 304
response is generated.
Now in javascript:-
// A good implementation would do error checking but this'll work
function getXML(url)
{
if (window.XMLHttpRequest)
oXmlHttp = new XMLHttpRequest()
else
oXmlHttp = new ActiveXObject("MSXML2.XMLHTTP.3.0")
oXmlHttp.open "GET", url, false
oXmlHttp.send
return oXmlHttp.ResponseXML
}
If this is the only application you'd have for the XML I would be tempted to
make your XML look like this:-
<select id="cboCity" name="city">
<option value="postcode">City Name</option>
<option value="postcode">City Name</option>
.
.
.
</select>
Now in HTML you would have:-
<body onload="body_onload()">
<form id="frmName" name="name" ...>
<span id="spnCity"></span>
.
.
.
</form>
</body>
Now the body_onload function would look like:-
function body_onload()
{
var xmlCity = getXML("cities.xml")
var spnCity = document.getElementById("spnCity")
if (spnCity.ownerDocument.importNode)
spnCity.appendChild(spnCity.ownerDocument.importNode(xmlCity.documentElement
)
else
spnCity.innerHTML = xmlCity.xml
}
When the page has been hit once the XML will be cached locally. Subsquent
requests will most likely pull the version from the cache.
The code may need refining for to work with a broader range of browsers.
After outlining all that, a Select box containing 2800 entries isn't a good
UI choice. You could make the XML more heirarchical and be smarter about
populating a couple of Selects.
--
Anthony Jones - MVP ASP/ASP.NET