Add custom field to contact in Xamarin Android - xamarin.android

Question

I'd like to add an custom field to contacts for permission management in my app.
f.e. Contact => Name, Number, Permission ("allowed"/"denied")
In my App I have a part which can receive commands by SMS.
Now I want to add a "Permission Management".
So that SMS from users, which are not allowed to send commands, not would be processed.
The "Permission Management" I'd like to realize with a custom field in the contactlist.
f.e. Contact => Name, Number, Permission ("allowed"/"denied")
Who can I add (programmatically) a custom filed to a contact?
(look at method "AddFieldtoContact" in ContactHelper.cs)
I found a solution where a custom mime type must be added: How to add new field(s) to the contact?
How can I add a custom mime type to add it in a contact?
-----------------------------------------------------------------------------
File StatusInAppPermission.cs
namespace Appname.Models
{
public class StatusInAppPermission
{
public const string Allowed = "allowed";
public const string Denied = "denied";
public const string NotSet = "notset";
public string Status = "";
public StatusInAppPermission(string sta)
{
switch (sta)
{
case Allowed:
Status = Allowed;
break;
case Denied:
Status = Denied;
break;
case NotSet:
Status = NotSet;
break;
default:
Status = NotSet;
break;
}
}
}
}
-----------------------------------------------------------------------------
File Contact.cs
namespace Appname.Models
{
public class Contact
{
public int Id { get; set; }
public string DisplayName { get; set; }
public string Number { get; set; }
public StatusInAppPermission StatusPermission { get; set; }
}
}
-----------------------------------------------------------------------------
File ContactHelper.cs
using Android.Provider;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Appname.Interfaces;
using Appname.Models;
using Xamarin.Forms;
[assembly: Xamarin.Forms.Dependency(typeof(Appname.Droid.ContactHelper))]
namespace Appname.Droid
{
class ContactHelper : IContactHelper
{
public async Task<List<Contact>> GetDeviceContactsAsync()
{
Contact selectedContact = new Contact();
List<Contact> contactList = new List<Contact>();
var uri = ContactsContract.CommonDataKinds.Phone.ContentUri;
//TODO: Add element for custom field "AppnamePermission"
string[] projection = { ContactsContract.Contacts.InterfaceConsts.Id, ContactsContract.Contacts.InterfaceConsts.DisplayName, ContactsContract.CommonDataKinds.Phone.Number /*, custom field "AppnamePermission" */ };
var cursor = Forms.Context.ContentResolver.Query(
uri,
projection,
null,
null,
ContactsContract.ContactsColumns.DisplayName + " ASC");
if (cursor.MoveToFirst())
{
do
{
// Get StatusInAppPermission from contact if saved
string status = "";
try
{
//TODO: Get custom field "AppnamePermission" value if exists
status = cursor.GetString(cursor.GetColumnIndex(projection[3]));
}
catch (Exception ex) { }
// Create new contact-object and add it to a List
contactList.Add(new Contact()
{
Id = cursor.GetInt(cursor.GetColumnIndex(projection[0]))
,DisplayName = cursor.GetString(cursor.GetColumnIndex(projection[1]))
,Number = cursor.GetString(cursor.GetColumnIndex(projection[2])).Replace("(", "").Replace(")", "").Replace("-", "").Replace(" ", "")
,StatusPermission = new StatusInAppPermission(status)
});
} while (cursor.MoveToNext());
}
return contactList;
}
public async Task<Contact> GetDeviceContactByNumber(string Number)
{
Contact selectedContact = new Contact();
List<Contact> contactList = new List<Contact>();
contactList = await GetDeviceContactsAsync();
foreach (Contact c in contactList)
{
if (c.Number.Equals(Number))
{
selectedContact = c;
}
}
return selectedContact;
}
public void AddFieldtoContact(Contact contact, string fieldname, string fieldvalue)
{
int ContactId = contact.Id;
// f.i. add fieldvalue by ContactId and fieldname
// fieldname => mimetype
// replace "clsContacts.FORMALITY_MIMETYPE" with mimetype
// the following code is adapted from: https://stackoverflow.com/questions/2733589/how-to-add-new-fields-to-the-contact
try
{
ContentValues values = new ContentValues();
int mod = Forms.Context.ContentResolver.Update(
uri
,values
,Data.InterfaceConsts.RawContactId + "=" + ContactId + " AND "
+ Data.InterfaceConsts.Mimetype + "= '"
+ clsContacts.FORMALITY_MIMETYPE + "'", null);
if (mod == 0)
{
values.Put(Data.InterfaceConsts.RawContactId, ContactId);
values.Put(Data.InterfaceConsts.Mimetype, clsContacts.FORMALITY_MIMETYPE);
Forms.Context.ContentResolver.Insert(uri, values);
}
}
catch (Exception e)
{
}
}
public string GetFieldFromContact(Contact contact, string fieldname)
{
int ContactId = contact.Id;
string fieldvalue = "";
// f.i. get fieldvalue by ContactId and fieldname
return fieldvalue;
}
}
}