Question

I have an update panel with a timer control set up to automatically check for some data updates every minute or so.

If it sees that the data updates, it is set to call a local script with the serialized JSON data.

ScriptManager.RegisterStartupScript(UpdateField, GetType(HiddenField), ACTION_CheckHistoryVersion, "updateData(" & data & ");", True)

where “data” might look something like

{
   "someProperty":"foo",
   "someOtherProperty":"bar",
   "someList":[
     {"prop1":"value"},
     {"prop2":"value"}, ...
   ],
   "someOtherList":[{},...,{}]
}

“data” can get quite large, and sometimes only a few items change.

The problem I am having is this. Every time I send this back to the client, it gets added as a brand new script block and the existing blocks do not get removed or replaced.

output looks something like this:

<script type="text/javascript">
  updateData({
       "someProperty":"foo",
       "someOtherProperty":"bar",
       "someList":[
         {"prop1":"value"},
         {"prop2":"value"}, ...
       ],
       "someOtherList":[{},...,{}]
    });
</script>
<script type="text/javascript">
  updateData({
       "someProperty":"foo",
       "someOtherProperty":"bar",
       "someList":[
         {"prop1":"changed"},
         {"prop2":"val"}, ...
       ],
       "someOtherList":[{},...,{}]
    });
</script>
<script type="text/javascript">
  updateData({
       "someProperty":"foos",
       "someOtherProperty":"ball",
       "someList":[
         {"prop1":"changed"},
         {"prop2":"val"}, ...
       ]
    });
</script>

with a new script block being created every time there is a change in the data.

Over time the amount of data accumulating on the browser could get potentially huge if we just keep adding this and I can’t imagine how most people’s browser would take it, but I don’t think it could be good.

Does anyone know if there is a way to just replace the code that has been sent back to the browser rather than continuously adding it like this?

Answer 1

I would recommend to use web service with some webmethod which you will call inside window.setInterval. In success handler of your webmethod (on client side) you can just take response and do whatever you want with it. And it will not be saved in your page (well, if you will do everything wrong). Benefit is that you will minimize request size(updatepanel will pass all your viewstate data, which could be large enough) and will limit server resources usage (update panel is causing full page live cycle, suppose slightly modified, but anyway – all those page_load, page_init, etc…) and with web service you will only what you need.

Here is an article where you can see how it could be created and used on client side. Looks like good enough.