One of my tile providers is never called in offline mode (Worked in 3.0.5.)

[GoogleCodeExporter]

What steps will reproduce the problem?
I don't think I can explain this problem on a step by step basis, because I 
don't completely understand it, so let's try with a brief description. 

I instantiate three tile providers and add them to the mTileProviderList. Two 
of them are of the type MapTileFileSystemProvider (one is used for cache 
providing and the other for actual user downloaded offline map tiles providing) 
and a MapTileNetworkProvider, which fetches the tiles from the tile server you 
guys so kindly maintain.

In the case when there is no map tile available from the two 
FileSystemProviders, We let the NetworkProvider handle this situation and 
return a locally generated tile which displays an 'offline' icon with short 
text 'not available in offline mode'.

What is the expected output? What do you see instead?
With version 3.0.5. this worked exactly as described above, but with 3.0.10., 
the NetworkProvider's (or rather, its inner TileLoader's) loadTile method is 
never even called, instead the FileSystemProvider's does, returns null and in 
the places where I have no actual tiles to display, the empty mapview 
background is shown.

What version of the product are you using? On what operating system?
I am using osmdroid-android-3.0.10, Eclipse SDK 4.2.2, Windows 7 x64 
Professional. Tested on three different android 4.0.3 devices.

Please provide any additional information below.
I'm guessing that it has something to do with the selection process of which 
TileProvider to use from the mTileProviderList. I've looked through the 
description here:
http://code.google.com/p/osmdroid/wiki/ModularTileProviderArchitecture

By the description it seems that all Providers are checked until one of them 
returns a tile or neither of them does. Since I haven't made any changes other 
than switching from osmdroid-android 3.0.5., where it worked, to 3.0.10., where 
it doesn't, the obvious conclusion to me is that you guys somehow changed the 
selection process and right now I don't fully understand how. Could you point 
me in the right direction pleas? In the mean time I'll give it another shot in 
trying to figure it out on my own. Thanks in advance!

Original issue reported on code.google.com by matej.di...@gmail.com on 14 May 2013 at 12:06

[GoogleCodeExporter]

Tell me what your NetworkProvider is - is it a TileDownloader subclass, a 
completely custom modular tile provider, etc...

It sounds like you have an "offline" mode for your app - how are you setting 
that?

Finally what TileSource are you using?

Some possible reasons a tile provider would not get called include:
 * If osmdroid is offline, the TileDownloader class will be skipped.
 * If a tile provider can not service a zoom level (because of min/max zoom level of tile provider or tile source).

Original comment by kurtzm...@gmail.com on 14 May 2013 at 12:31

[GoogleCodeExporter]

Also note: "OnlineTileSourceBase classes are the only tile sources that the 
MapTileDownloader can serve."

Original comment by kurtzm...@gmail.com on 14 May 2013 at 12:31

[GoogleCodeExporter]

Thanks for the quick response!

You helped me narrow it down :)

I have a NetworkManager singleton which keeps track of network state for the 
app. There are three states in the state enum, ONLINE, OFFLINE and UNAVAILABLE. 
Whenever an action is about to be performed which depends on, or alters the 
network state, the state is updated and returned to the caller so adequate 
actions can be taken depending on which state the app is in.

My NetworkProvider is a direct subclass of MapTileModuleProviderBase, and not 
of TileDownloader. My TileSource is of type OnlineTileSourceBase. Based on 
these two things I deduced that it probably has nothing to do with two of the 
three points you mentioned:
- If osmdroid is offline, the TileDownloader class will be skipped.
- OnlineTileSourceBase classes are the only tile sources that the 
MapTileDownloader can serve.

Which left me with:

- If a tile provider can not service a zoom level (because of min/max zoom 
level of tile provider or tile source) it might not be called

How my NetworkProvider was supposed to work is that if the current mode is not 
OFFLINE and the tileSource us not null, then the respective min and max zoom 
levels from the source are returned. Otherwise the Provider will give the 
maximum possible zoom level for getMaximumZoomLevel and minimum possible zoom 
level for getMinimumZoomLevel, so it will be always used because it can provide 
tiles for all the zoom levels, and how it does this is that for offline mode it 
generates tiles with an offline icon on them to let the user know that he can't 
see them because of his network state.

The screw-up was in the getMinZoomLevel and getMaxZoomLevel methods, as they 
returned the exact opposite of what they were supposed to return, in the case 
the app is offline (Min returned the max value and Max returned the min value, 
so it was never used for offline cases). 

Why this worked before I have no idea, but I'm new on the project that I'm 
working on, which has an extensive preexisting code base, so I'm still getting 
the hang of things finding my way around.

I hope this helps anyone who might have a similar issue somewhere down the line.

Once again, thank you for the quick responses and for the useful pointers :)

Original comment by matej.di...@gmail.com on 14 May 2013 at 2:19

[GoogleCodeExporter]

Good to hear! The behavior where tile modules are skipped if they can not 
service a zoom level is a relatively new change (3.0.9?) so it probably didn't 
manifest itself in the past. It is an optimization - if a tile module can not 
service a zoom level, then there is no reason to call it. This is particularly 
useful for TileDownloaders so they don't bother putting network traffic out 
there that will only result in a 404.

It sounds like this issue can be closed.

Original comment by kurtzm...@gmail.com on 15 May 2013 at 1:11

• Changed state: Fixed