topic Caching in ArcGIS API for Flex Questions

Pan/Zoom Event

JustinWilliams — Fri, 09 Apr 2010 17:17:31 GMT

Just curious, if anyone has run into this before...

I have a National Weather Service radar layer which is being auto-refreshed at a specific interval. There seems to be an issue with the layer's refresh not overriding a cached image from the current zoom/extent. I have tried everything possible to remedy this, including rewriting my refresh method to construct an entire new layer and add it to the map.

So... I am curious. What event is firing when I zoom/pan, as this is the only action which will draw the latest data.

Any help would be appreciated!

Thanks,

Justin
GIS Analyst
Indiana Department of Homeland Security

Pan/Zoom Event

RobertScheitlin__GISP — Fri, 09 Apr 2010 17:33:07 GMT

Justin,

Have you set the disableClientCaching to false on the layer (That is if it is a ArcGISDynamicMapServiceLayer)?

Caching

JustinWilliams — Fri, 09 Apr 2010 18:17:07 GMT

Yeah I've tried that and the cachePolicy = "off"

Another odd behavior is when the browser loads, it will always load old data and remains that way until you zoom/pan. It makes me think there is something going on with flash/flex in rebuilding a cached tile/image of the current screen extent.

Fixed... sort of

JustinWilliams — Fri, 09 Apr 2010 19:25:03 GMT

Ok changes are being reflected by forcing a non-noticeable pan on the map(not sure if this pan is even taking place honestly, however my data is clearly being updated). However a new unintended behavior has occurred and my thinking leads me to believe this is another caching issue.

Here is an example of the event handler I am using to refresh one category of data. I have three other categories which can fire. When the other events fire, and refresh other layers, they revert all other layers to their previous outdated versions if the layer being refreshed has no new data. Any ideas on how to avoid/deal with this?

      //customized - the refresh handlers for the refresh categories
      private function critical_refresh_Handler(event:TimerEvent):void {
       var i:int = 0;
       var refresh_layer:ArcGISDynamicMapServiceLayer;
       //critical refreshes
       while( i < critical_live_layers.length) {
     refresh_layer = map.getLayer(critical_live_layers) as ArcGISDynamicMapServiceLayer;
     refresh_layer.refresh();
     i++
       }
       //pans the map to get the new data to draw, workaround to caching issue with flex/flash currently unknown.
    map.panDuration = 1;
    map.panDown();
    map.panUp();

      }

autorefresh

JustinWilliams — Fri, 09 Apr 2010 20:05:59 GMT

this seemed to fix the issue

      private function critical_refresh_Handler(event:TimerEvent):void {
       var i:int = 0;
       var refresh_layer:ArcGISDynamicMapServiceLayer;
       map.panEnabled = true;
    map.panDuration = 15;

    map.panDown();
       //critical refreshes
       while( i < critical_live_layers.length) {
     refresh_layer = map.getLayer(critical_live_layers) as ArcGISDynamicMapServiceLayer;
     refresh_layer.refresh();
     i++
       }
    map.panUp();
      }

Pan/Zoom Event

DasaPaddock — Fri, 09 Apr 2010 20:46:05 GMT

Have you tried setting disableClientCaching to true? This should prevent the browser from using it's own cache instead of going back to the server.
See:
http://resources.esri.com/help/9.3/arcgisserver/apis/flex/apiref/com/esri/ags/layers/ArcGISDynamicMapServiceLayer.html#disableClientCaching

Pan/Zoom Event

HessCorporation — Wed, 14 Apr 2010 09:32:52 GMT

I'm also having this problem but with a custom WMS layer for national weather radar, so there is no disabledClientCaching option.

I'll try your fix as i think that will work...very strange problem though as all the settings to disable caching are set.

Just out of interest where are you sourcing your weather radar from? i'm using the nexrad feed from Iowa State but i'd like an AGS version if possible.

http://mesonet.agron.iastate.edu/ogc/

Pan/Zoom Event

DasaPaddock — Wed, 14 Apr 2010 16:22:23 GMT

You could try a similar fix by implementing the same thing in your custom layer. When disableClientCaching is true, it just adds a _ts url parameter with the current time. This way every url requested is different.

Code:
reqVars._ts = new Date().time

Radar services

JustinWilliams — Wed, 14 Apr 2010 17:55:46 GMT

Use add data and GIS Servers/WMS Service for this, has some neat layers for use

http://www.mapcontext.com/cgi-bin/wms.cgi?REQUEST=GetCapabilities&SERVICE=WMS&

Pan/Zoom Event

HessCorporation — Fri, 16 Apr 2010 13:24:26 GMT

You could try a similar fix by implementing the same thing in your custom layer. When disableClientCaching is true, it just adds a _ts url parameter with the current time. This way every url requested is different.

Code:
reqVars._ts = new Date().time

The problem doesn't seem to be with client caching, i added that to the URL params but it just doesn't reload the layer when .refresh is fired, the same _ts value is returned every time. If i move the map then it does use a new _ts value and updates the map.

So i'm pretty sure the problem is with the refresh method, i'm using the custom WMS layer from the sample flex viewer. It seems to set the params the first time the layer is loaded, but the refresh command doesn't force a new URLRequest load.

Not sure if this is the same problem for the OP's feed, but from looking at the history of this issue on both forums it always seems to involve radar feeds and WMS. I'm wondering if WMS feeds just work differently and can't utilise refresh().

Re: Pan/Zoom Event

CoreySchafer — Sat, 11 Dec 2021 14:29:47 GMT

Has anyone found a solution to this? I am having the same problem. I have even added in the map.Pan functions without any success. I have set my disableClientCaching = true and then refresh the layer with no luck:

private function refreshLayers():void
   {
                                var pd:Number = map.panDuration;
    map.panDuration = 15;
    var layers:Array = getLayers();
    for each(var layer:Object in layers)
    {
     var dLayer:ArcGISDynamicMapServiceLayer = layer as ArcGISDynamicMapServiceLayer;
     dLayer.disableClientCaching = true;
   
     map.panDown();
     dLayer.refresh();
     map.panUp();
     }
    } 
    map.panDuration = pd;
}

I can run this function as much as I want with updating to the weather. The weather only updates when I Pan or Zoom the map. I can see in FireBug that the refresh function is sending some requests (I'm assuming two because of the two pan functions I am calling), but I'm not sure why the map is not updating. Picture 1 is a non-updated Map. Picture 2 is what I get in Firebug when I call the refresh function above. Picture 3 is What I get in Firebug when I very slightly Pan the map, and Picture 4 is the updated Weather I get after the Pan.

I would like to have a function that updates this weather for me and as of now am stumped as to why this isn't working. Any help will be appreciated...

Re: Pan/Zoom Event

CoreySchafer — Mon, 13 Jun 2011 18:33:52 GMT

After a little more investigation, it seem that images are getting cached for specific extents. For example, when I first load my map, I am getting the same image every time because my map loads the same initial extent every time. If I use the buttons in the Navigatoion to pan left and right, I will get images that I have previously seen as well as long as I have panned there before.

I only get the newest weather maps when I either pan somewhere I have not previously panned or if I move the map around with my cursor (even slightly will send a different extent and therefore causes the map to update). So it definitely seems like a caching issue. Just not sure why it is still doing it...