无法应用FragmentTransaction中的add()？

由于以下错误无法添加到片段事务,您将如何进行此操作？

add() in FragmentTransaction cannot be applied to:
Expected Parameters: Actual Arguments:
int R.id.mapWithOverlay  
android.support.v4.app.Fragment _mapFragment  (com.google.android.gms.maps.MapFragment)
String "map"

代码如下:

android.support.v4.app.FragmentTransaction fragTx = getSupportFragmentManager().beginTransaction();
if (fragTx != null) {
     _mapFragment = MapFragment.newInstance(mapOptions);
     fragTx.add(R.id.mapWithOverlay, _mapFragment, "map");
     fragTx.commit();
} else {
     Toast.makeText(this, "Could not display the map", Toast.LENGTH_SHORT).show();
}

提前致谢.