getImageWithCancelLoadingSupport method

ImageProvider<Object> getImageWithCancelLoadingSupport(
  1. TileCoordinates coordinates,
  2. TileLayer options,
  3. Future<void> cancelLoading
)
inherited

Retrieve a tile as an image, based on its coordinates and the TileLayer

For this method to be called instead of getImage, supportsCancelLoading must be overriden to true.

Usually redirects to a custom ImageProvider, with one parameter using getTileUrl, and one using cancelLoading.

For many implementations, this is the only method that will need implementing.

Supports cancelling loading tiles, which is designed to allow for implementations that can cancel HTTP requests or other processing in-flight, when the underlying tile is disposed before it is loaded. This may increase performance, and may decrease unnecessary tile requests. Note that this only applies to the web platform.

The cancelLoading future will complete when the underlying tile is disposed/pruned. The implementation should therefore listen for its completion, then cancel the loading. If an image Codec is required, decode transparentImage - it will never be visible anyway. Note that cancelLoading will always be completed on disposal, even if the tile has been fully loaded, but this side effect is not usually an issue.

See this example with 'package:dio's CancelToken:

final cancelToken = CancelToken();
cancelLoading.then((_) => cancelToken.cancel());

Implementation

ImageProvider getImageWithCancelLoadingSupport(
  TileCoordinates coordinates,
  TileLayer options,
  Future<void> cancelLoading,
) {
  throw UnimplementedError(
    'A `TileProvider` that overrides `supportsCancelLoading` to `true` must '
    'override `getImageWithCancelLoadingSupport`',
  );
}