Cant import android files in gluon mobile

问题:

my problem is that

import android.content.res.AssetFileDescriptor;
import android.media.AudioManager;
import javafx.scene.media.MediaPlayer;
import javafxports.android.FXActivity;

return The import android cannot be resolved. although the class containing those imports is inside the android folder in the gluon single view project and the sdk is referenced.