c# - PCLStorage FileSystem is only available in Android, not iOS -

i'm writing cross platform application in xamarin, android , ios, , need save text files local storage. i'm using pclstorage, whenever mouse on pclstorage code, says "myapplication.android: available, myapplication.ios not available". how can use pclstorage store files on both platforms? or there way can this? here's example of of code:

public async task createrealfileasync(string filename, string filebody)     {         // hold of file system         ifolder rootfolder = filesystem.current.localstorage;          // create folder, if 1 not exist         ifolder folder = await rootfolder.createfolderasync("dadappfiles", creationcollisionoption.openifexists);          // create file, overwriting existing file         ifile file = await folder.createfileasync(filename, creationcollisionoption.replaceexisting);          // populate file text         await file.writealltextasync(filebody);     }