You should not be storing the full sprite in string, you should create some kind of ID for a sprite in a scriptableObject or something and save that in the extras. I created a little class that helps me store data in a single string in a KvP way, hope it helps:
public class SingleStringKvP
{
private readonly Dictionary<string, string> _kvPairs = new();
private const char PairSeparator = ';';
private const char KeyValueSeparator = ':';
public SingleStringKvP(string startingValue)
{
Parse(startingValue);
}
public SingleStringKvP()
{
}
public void AddValue(string key, string value)
{
_kvPairs[key] = value;
}
public string GetValue(string key)
{
return _kvPairs.TryGetValue(key, out var value) ? value : string.Empty;
}
public override string ToString()
{
var builder = new StringBuilder();
foreach (var kvp in _kvPairs)
{
if (builder.Length > 0)
builder.Append(PairSeparator);
builder.Append($"{kvp.Key}{KeyValueSeparator}{kvp.Value}");
}
return builder.ToString();
}
private void Parse(string startingValue)
{
if (string.IsNullOrEmpty(startingValue)) return;
var pairs = startingValue.Split(PairSeparator);
foreach (var pair in pairs)
{
var kv = pair.Split(KeyValueSeparator);
if (kv.Length == 2)
{
var key = kv[0];
var value = kv[1];
AddValue(key, value);
}
}
}
}