Hi Max.
There are a couple of things that could help (this all applies to image tile layers - vector tile layers are a different beast, but I don't think that's what you're dealing with here).
First, you should make sure you look at the mapServiceInfo property of the AGSArcGISTiledLayer. It gives you an AGSArcGISMapServiceInfo object that has a maxExportTilesCount property. That is the limit that you need to stay below. Note, AGSExportTileCacheTask also has a mapServiceInfo property you can use.
To see how many tiles an area will attempt to download, you can always use the AGSExportTileCacheTask.estimateTileCacheJobWithParameters() call to create a job that you can run to get the tile count back for the extent/geometry your user has drawn, but that's not very realtime. For that, you could make use of this bit of code. It'll need a bit of modification (e.g. I haven't yet included a method to get a total number of tiles across multiple LODs) but it works pretty well. Also, I haven't tested it in anger, so I would recommend you check it against actual estimate calls for accuracy.
And as Kris mentioned, make sure you use the levelIDs property of the AGSExportTileCacheParameters object to reduce tiles. For most tile schemes, each higher level of LOD will need 4x the number of tiles, so as you zoom in, you really ramp up the tile count.
Vector tiles are quite different, and I don't have an easy solution for that:
- There is no "estimate" method on the service.
- Vector tiles are highly optimized by content and are not uniform like the image tile schemes are (we optimize heavily with overzoom where we can). See the ArcGIS Pro Create Vector Tile Index documentation for an illustration of what I mean.
Hope this helps.
