Creating New Tile Providers

One common requirement is a custom TileProvider, and potentially a custom ImageProvider inside. This will allow your plugin to intercept all tile requests made by a map, and take your own action(s), before finally returning a tile.

Check the Plugins List for providers that already implement the behaviour you wish to replicate.

1. Extending TileProvider

To create your own usable TileProvider, the first step is making a class that extends the abstract class, and adding a constructor.

The constructor should accept an argument of super.headers, without a constant default.

class CustomTileProvider extends TileProvider {
    CustomTileProvider({
        // Suitably initialise your own custom properties
        super.headers, // Accept a `Map` of custom HTTP headers
    })
}

If using an object that needs closing/cancelling, such as an HttpClient, override the dispose method.

2. Setup Tile Retrieval

TileProviders must implement a method to return an ImageProvider (the image of a tile), given its coordinates and the TileLayer it is used within.

It is best to put as much logic as possible into a custom ImageProvider, to avoid blocking the main thread.

There's two methods that could be called by flutter_map internals to retrieve a tile: getImage or getImageWithCancelLoadingSupport.

Prefer overriding getImageWithCancelLoadingSupport for TileProviders that can cancel the loading of a tile in-flight, if the tile is pruned before it is fully loaded. An example of a provider that may be able to do this is one that makes HTTP requests, as HTTP requests can be aborted on the web (although Dart does not 'natively' support it yet, so a library such as Dio is necessary). Otherwise, getImage must be overridden.

With Cancel Loading Support

In addition to the coordinates and TileLayer, the method also takes a Future<void> that is completed when the tile is pruned. It should be listened to for completion (for example, with then), then used to trigger the cancellation.

For an example of this, see CancellableNetworkTileProvider.

    @override
    bool get supportsCancelLoading => true;
    
    @override
    ImageProvider getImageWithCancelLoadingSupport(
        TileCoordinates coordinates,
        TileLayer options,
        Future<void> cancelLoading,
    ) =>
        CustomCancellableImageProvider(
            url: getTileUrl(coordinates, options),
            fallbackUrl: getTileFallbackUrl(coordinates, options),
            cancelLoading: cancelLoading,
            tileProvider: this,
        );

Without Cancel Loading Support

    @override
    ImageProvider getImage(TileCoordinates coordinates, TileLayer options) =>
        CustomImageProvider(
            url: getTileUrl(coordinates, options),
            fallbackUrl: getTileFallbackUrl(coordinates, options),
            tileProvider: this,
        );

If developing a plugin, you may wish to adjust the 'User-Agent' header has been to further differentiate your plugin's traffic from vanilla 'flutter_map' traffic.

(Optionally) Override URL Generation

Some custom TileProviders may want to change the way URLs are generated for tiles, given a coordinate.

It's possible to override:

• how the urlTemplate's placeholders are populated: populateTemplatePlaceholders

• the values used to populate those placeholders: generateReplacementMap

• the generation method itself: getTileUrl and/or getTileFallbackUrl

Avoid overriding the generation method itself, as it is not usually necessary.