Add contents of geoJson file to vector layer after download - openlayers-3

Question

I want to download features in geoJson format from a service and then add the features in it to a new layer on my map. I can download the features ok, I'm stuck as to how to add them to the map after the download.
I do not want to let OL read the file directly from the url as shown in every example I can find, since I want more control over when the features will be downloaded or what to do if the download fails for some reason.
I'm trying this (data contains my geoJson featurecollection):
var nwLayer = new ol.layer.Vector({
title: 'My Title',
source: new ol.source.Vector({
features: data.features,
format: new ol.format.GeoJSON()
}),
style: new ol.style.Style({
image: new ol.style.Circle({
radius: 7,
fill: new ol.style.Fill( { color: "yellow" } )
})
})
} );
map.addLayer(nwLayer);
This results in an error somewhere inside the ol library, apparently the ol feature type is not the same as a geoJson feature, it requires a getId() function.
I also tried to add the data as a whole:
features: data,
This has no visual effect at all.
How can I do this?

Answer 1

You are correct, OpenLayer features are not GeoJSON feature objects. To transform GeoJSON to OpenLayers features, use the readFeatures method of ol.format.GeoJSON.
With the rest of your example code:
var nwLayer = new ol.layer.Vector({
title: 'My Title',
source: new ol.source.Vector({
features: (new ol.format.GeoJSON()).readFeatures(data)
}),
style: new ol.style.Style({
image: new ol.style.Circle({
radius: 7,
fill: new ol.style.Fill( { color: "yellow" } )
})
})
});
map.addLayer(nwLayer);