[OpenLayers-Dev] Lost scope in tileUrlFunction when extending ol.source.VectorTile (MVT)

[Christian Mayer]

Hi all,

I extended the class ol.source.VectorTile in order to load VectorTiles
in different formats (GeoJSON and MVT) from a local GWC cache. While
upgrading from OpenLayers v3.20 to OpenLayers v4.x it seems that for MVT
the scope in the "tileUrlFunction" gets lost. It seems to be "window".
For GeoJSON-based VectorTiles everything is still running fine.

Below you find the crutial parts of my class:

ol.inherits(ol.source.GWCVT, ol.source.VectorTile);

ol.source.GWCVT.prototype.tileUrlFunction =
    function(tileCoord, pixelRatio, projection) {

// here 'this' becomes 'window' in the second call

// assembling the URL
// ...

}

ol.source.GWCVT.prototype.setTileUrlFunction = function(tileUrlFunction) {

  ol.source.VectorTile.prototype.setTileUrlFunction.call(this,
tileUrlFunction);
};

Thanks for any hint!

Cheers
Chris
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