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

[Christian Mayer]

Hi Roman,

you are absolutely right and your explanation brings it to the point. I
wasn't aware that the 'tileUrlFunction' should not be overwritten
directly. I changed my code according to your suggestion it works perfectly.

Thanks you very much! Great help!

Cheers
Chris


On 12.10.2017 14:48, Roman Zoller wrote:
> As far as I understand, the ol.source.VectorTile class wasn't
> specifically designed to have tileUrlFunction as a function that can
> be overriden and that will be called with a specific this context.
>
> I think the general idea is that you can just pass any function as
> options.tileUrlFunction, and it just happened to be called with a this
> context of the class before version 4.2.0, but I guess this was never
> really an intended feature.
>
> For your specific issue, I think you could rename the function in your
> class to avoid confusion, e.g.
>
> ol.source.GWCVT.prototype.defaultTileUrlFunction =
>     function(tileCoord, pixelRatio, projection) {
>   // ...
> };
>
> and then pass it as options.tileUrlFunction to the super class in your
> constructor, with correctly bound this:
>
> ol.source.GWCVT = function(options) {
>   var tileUrlFunction = options.tileUrlFunction ||
> this.defaultTileUrlFunction.bind(this);
>
>   ol.source.VectorTile.call(this, {
>     tileUrlFunction: tileUrlFunction,
>     ...
>   });
> };
>
> Hope that helps!
>
> Cheers,
>
> Roman
>
> On Thu, Oct 12, 2017 at 2:33 PM, Christian Mayer <ml-cm at meggsimum.de
> <mailto:ml-cm at meggsimum.de>> wrote:
>
>     Hi again,
>
>     here is some more information in addition to my previous mail:
>
>     The problem occurs for VectorTiles in GeoJSON format as well. So
>     there must be a more general problem with extending the
>     ol.source.VectorTile (or the way I do it).
>     The change / problem seems to be introduced with Version 4.2.0.
>     With version 4.1.1 everything works as expected.
>
>     Cheers
>     Chris
>
>
>     On 12.10.2017 13:45, Christian Mayer wrote:
>>
>>     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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