Android get user account email (but not work)

GetAccountPlugin.java

import android.accounts.AccountManager;
import android.accounts.Account;

public class GetAccountPlugin {
	//CANNOT GET CORRECT PURCHASED USER'S EMAIL
	public String GetGoogleAccountEmail(Activity activity){
		AccountManager manager = (AccountManager) activity.getSystemService(Context.ACCOUNT_SERVICE);
		Account[] accounts =  manager.getAccounts();
		//Log.d(tag, "GetGoogleAccountEmail-LENGTH " + accounts.length);
		String strGmail = "";
		
		for (Account account : accounts) {
			String possibleEmail = account.name;
			String type = account.type;
			
			if (type.equals("com.google")) {
					strGmail = possibleEmail;
					//Log.d(tag, "GetGoogleAccountEmail-GMAIL " + strGmail);
					break;
			}
		}
		return strGmail;
	}
}