I have a project in OpenLayers 8.2, where there are many types of layers in a map. As introduced in ol 6.14, I am using the 'loadstart' and 'loadend' events of the map object (https://openlayers.org/en/latest/examples/load-events.html).
import { Map, View } from 'ol'
this.map = new Map({
...
});
this.map.on('loadstart', () => {
console.warn("loadstart");
});
This fires flawlessly for most kinds of layers (TileWMS, ImageWMS, XYZ) but it doesn't work for vector layer. Vector layer is using VectorSource with custom loader function, which sends a request to the data service with each change of a current extent.
import sourceVector from 'ol/source/Vector'
let vectorSource = new sourceVector({
loader: function (extent, resolution, projection) {
let features = // fetch data using current extent
this.addFeatures(features);
}
});
I would expect, that when a loader function is called for the vector source, the 'loadstart' event would be triggered for the map object. Is that a potential bug or am I understanding it wrong? Or is there a manual way of letting the map know, that my vector layer is being loaded?
Thanks for any hints, Vojtech
When using a custom loader
, you need to handle two additional arguments to make loadend
events work: a success
and a failure
callback:
import sourceVector from 'ol/source/Vector'
let vectorSource = new sourceVector({
loader: function (extent, resolution, projection, success, failure) {
try {
let features = // fetch data using current extent
this.addFeatures(features);
success(features);
} catch(e) {
vectorSource.removeLoadedExtent(extent);
failure();
}
}
});
Also see the API docs for the Vector source: https://openlayers.org/en/v8.1.0/apidoc/module-ol_source_Vector-VectorSource.html.