Openlayers & Cordova,openlayers cannot load app's local kml file with cdvfile

1. Recently, using cordova+openlayers to develop an ios map application, we encountered the problem that openlayers could not read the kml file in ios"s library folder,
2. Code
var cdvfile = "cdv file://localhost/library-nosync/A111/5000.KML";
var relativePath = "static/kml/5000.KML";
let vector = new ol.layer.Vector ({

)

source: new ol.source.Vector({
    url: relativePath,  //kml
    //url: cdvfile,    //
    format: new ol.format.KML()
})

});
3. Using the relative path can read the kml, but the relative path is packaged in the applicationDirectory of ios, which belongs to the application file, which must be unreasonable; using cdvfile to read the kml in the Libary/NoCloud cannot be obtained, the created vector object is empty, and the most important thing is that there are no printing errors on the console.
4. Is there any way to make openlayers load the kml file in Libary successfully in iOS?

Technology platform: cordova, openlayers4, Cordova-plugin-file, ios