AFAIK the files in the assets directory don’t get unpacked.
Instead, they are read directly from the APK (ZIP) file.
So, you really can’t make stuff that expects a file accept an asset ‘file’.
Instead, you’ll have to extract the asset and write it to a seperate file, like Dumitru suggests:
File f = new File(getCacheDir()+"/m1.map");
if (!f.exists()) try {
InputStream is = getAssets().open("m1.map");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
FileOutputStream fos = new FileOutputStream(f);
fos.write(buffer);
fos.close();
} catch (Exception e) { throw new RuntimeException(e); }
mapView.setMapFile(f.getPath());