I am getting below error when try to rebuild the project in release mode.

Severity Code Description Project File Line Suppression State
Error (active) CS8795 Partial method ‘MyContactsService.GetContactsAsync()’ must have an implementation part because it has accessibility modifiers. ContactsDemo (net8.0-maccatalyst), ContactsDemo (net8.0-windows10.0.19041.0)

Because of the above error I can’t create the APK file.

I am using a service to fetch the local phone book contacts and that class causes this error. Check the below class:

namespace ContactsDemo.Service
{
    public partial class MyContactsService
    {
        public partial List<MyContact> GetContactsAsync();
    }
}

We have added the service classes on both Android and iOS platforms.

Android Service

namespace ContactsDemo.Service
{
    public partial class MyContactsService 
    {
        const string ThumbnailPrefix = "thumb";
        List<MyContact> contactList;
        public partial List<MyContact> GetContactsAsync()
        {
            FillContacts();
            return contactList;
        }

        void FillContacts()
        {
            var uri = ContactsContract.Contacts.ContentUri;

            string[] projection = {
                ContactsContract.Contacts.InterfaceConsts.Id,
                ContactsContract.Contacts.InterfaceConsts.DisplayName,
                ContactsContract.Contacts.InterfaceConsts.PhotoId,
            };


            var ctx = Android.App.Application.Context;

            var cursor = ctx.ApplicationContext.ContentResolver.Query(uri, new string[]
{
                        ContactsContract.Contacts.InterfaceConsts.Id,
                        ContactsContract.Contacts.InterfaceConsts.DisplayName,
                        ContactsContract.Contacts.InterfaceConsts.PhotoThumbnailUri
}, null, null, $"{ContactsContract.Contacts.InterfaceConsts.DisplayName} ASC");

            contactList = new List<MyContact>();

            if (cursor.MoveToFirst())
            {
                do
                {
                    var contact = CreateContact(cursor, ctx);
                    if (!string.IsNullOrWhiteSpace(contact.Name))
                    {
                        contactList.Add(contact);
                    }
                } while (cursor.MoveToNext());
            }
        }

        MyContact CreateContact(ICursor cursor, Context ctx)
        {
            var contactId = GetString(cursor, ContactsContract.Contacts.InterfaceConsts.Id);

            var numbers = GetNumbers(ctx, contactId);
            var emails = GetEmails(ctx, contactId);

            var uri = GetString(cursor, ContactsContract.Contacts.InterfaceConsts.PhotoThumbnailUri);
            string path = null;
            if (!string.IsNullOrEmpty(uri))
            {
                try
                {
                    using (var stream = Android.App.Application.Context.ContentResolver.OpenInputStream(Android.Net.Uri.Parse(uri)))
                    {
                        path = Path.Combine(Path.GetTempPath(), $"{ThumbnailPrefix}-{Guid.NewGuid()}");
                        using (var fstream = new FileStream(path, FileMode.Create))
                        {
                            stream.CopyTo(fstream);
                            fstream.Close();
                        }

                        stream.Close();
                    }


                }
                catch (Exception ex)
                {
                    System.Diagnostics.Debug.WriteLine(ex);
                }

            }
            var contact = new MyContact
            {
                Name = GetString(cursor, ContactsContract.Contacts.InterfaceConsts.DisplayName),
                Emails = emails,
                Image = path,
                PhoneNumbers = numbers,
            };

            return contact;
        }

        string[] GetNumbers(Context ctx, string contactId)
        {
            var key = ContactsContract.CommonDataKinds.Phone.Number;

            var cursor = ctx.ApplicationContext.ContentResolver.Query(
                ContactsContract.CommonDataKinds.Phone.ContentUri,
                null,
                ContactsContract.CommonDataKinds.Phone.InterfaceConsts.ContactId + " = ?",
                new[] { contactId },
                null
            );

            return ReadCursorItems(cursor, key)?.ToArray();
        }

        string[] GetEmails(Context ctx, string contactId)
        {
            var key = ContactsContract.CommonDataKinds.Email.InterfaceConsts.Data;

            var cursor = ctx.ApplicationContext.ContentResolver.Query(
                ContactsContract.CommonDataKinds.Email.ContentUri,
                null,
                ContactsContract.CommonDataKinds.Email.InterfaceConsts.ContactId + " = ?",
                new[] { contactId },
                null);

            return ReadCursorItems(cursor, key)?.ToArray();
        }

        IEnumerable<string> ReadCursorItems(ICursor cursor, string key)
        {
            while (cursor.MoveToNext())
            {
                var value = GetString(cursor, key);
                yield return value;
            }

            cursor.Close();
        }

        string GetString(ICursor cursor, string key)
        {
            return cursor.GetString(cursor.GetColumnIndex(key));
        }

    }
}

iOS Service

namespace ContactsDemo.Service
{
    public partial class MyContactsService
    {
        const string ThumbnailPrefix = "thumb";

        List<MyContact> contacts = new List<MyContact>();

        public partial List<MyContact> GetContactsAsync()
        {
            NSError error = null;
            var keysToFetch = new[] { CNContactKey.PhoneNumbers, CNContactKey.GivenName, CNContactKey.FamilyName, CNContactKey.EmailAddresses, CNContactKey.ImageDataAvailable, CNContactKey.ThumbnailImageData };

            var request = new CNContactFetchRequest(keysToFetch: keysToFetch);
            request.SortOrder = CNContactSortOrder.GivenName;

            using (var store = new CNContactStore())
            {
                var result = store.EnumerateContacts(request, out error, new CNContactStoreListContactsHandler((CNContact c, ref bool stop) =>
                {

                    string path = null;
                    if (c.ImageDataAvailable)
                    {
                        path = path = Path.Combine(Path.GetTempPath(), $"{ThumbnailPrefix}-{Guid.NewGuid()}");

                        if (!File.Exists(path))
                        {
                            var imageData = c.ThumbnailImageData;
                            imageData?.Save(path, true);


                        }
                    }

                    var contact = new MyContact()
                    {
                        Name = string.IsNullOrEmpty(c.FamilyName) ? c.GivenName : $"{c.GivenName} {c.FamilyName}",
                        Image = path,
                        PhoneNumbers = c.PhoneNumbers?.Select(p => p?.Value?.StringValue).ToArray(),
                        Emails = c.EmailAddresses?.Select(p => p?.Value?.ToString()).ToArray(),

                    };

                    if (!string.IsNullOrWhiteSpace(contact.Name))
                    {
                        contacts.Add(contact);
                    }
                }));
            }

            return contacts;
        }
    }
}

I am able to run the app in debug mode with this error. But in release mode can’t rebuild the app and can’t create the APK file.

I have created a demo project for reproducing this issue.