MapGuide layer caches dynamic overlay

[ksgeograf]

A dynamic overlay in MapGuide is, as the name states, dynamic. The image is requested with a HTTP "GET" call, and is thus subjected to the browser cache. Since the layer can be changed by server code, the layer should refresh, when the map is refreshed.

OpenLayers use the "viewRequestID" to do this for other purposes. The attached path applies the "viewRequestID" to each request, so the layer is refreshed, whenever required by the map. The sequence number is assigned to the same queryString key that the official viewer uses, "SEQ", to prevent name clashes.

[crschmidt]

I don't think we should do this. In all other code, which can also change on the server side, we explicitly use the 'redraw(true)' function to redraw; this adds a salt to the URL. (i've just tested this with the mapguide code, and it does work.) I don't see any reason for MapGuide to be special in this way; using redraw(true) has the client able to control the caching of the layer.

Unless there's some reason that MapGuide is special here, I don't see the reason for it to be added here. If the standard "allow the client to determine when to avoid the cache' is insufficient, then I believe this patch is actually wider than just MapGuide: a 'never hit cache' property on the layer would be reasonable and allow for other layers to take advantage of it as well.

So, if you can provide an explanation of what makes MapGuide special here, this might be a valid ticket. However, I think it's better addressed as a lower level (Layer.HTTPRequest) feature request, or a documentation issue.

[ksgeograf]

I was not aware of the redraw(true) method.

redraw(true) does not work well for my usage, but I can see the rationale for not wanting to add my patch.