How to Save and Load a list of Scriptable Objects from a File?

Why overcomplicate this and not just use AssetDatabase? Using AssetDatabase.CreateAsset() you can save a scriptableobject to an asset file. At editor-time you can load it via AssetDatabase.LoadAssetAtPath() and you can also add it to any form of asset retrieval method (assetbundles, addressables ...) for loading at runtime. As your ScrptableObjects are not supposed to be altered at runtime, this should be the easiest way.

Saving and loading data can be done by writing and reading variables to and from a file. I will get to how you can do that later, but just a quick explanation on files.

Files can store data that contain text. This text could be a string, a number, a bool or byte etc. It's important to note that not all data types can be converted to a string perfectly. Therefore, we need to save a string that represents that data type, and when we read the file, we need to interpret that string correctly.

Let's take the example of saving the position of a game object to a file. You can't save the transform of the object, but you can save 3 floats that contain the x, y and z position of the object. Or use Vector3.ToString().

Reading and Writing from/to a file

You need to be using System.IO to perform operations on files.

Reading a file

You can use the File class to read all lines from the file into a single string, or use the StreamReader to read the file line by line, and perform operations on the line that is currently being read by the stream reader. For example:

     void ReadFile(string directory)
     {
         // Getting raw text
         string text = File.ReadAllText(directory);
 
         // Using a stream reader
         StreamReader reader = new StreamReader(directory);
 
         string line;
         while ((line = reader.ReadLine()) != null)
         {
             if (line == "Line 4: ")
             {
                 // Do stuff
             }
             // etc.
         }
     }

Writing to a file

You can write to a file using the File class or by using the StreamWriter as well:

     void WriteToFile(string directory)
     {
         // Overwrites any text already in the file
         File.WriteAllText(directory, "Hello world");
 
         // Adds on to the end of an existing file
         File.AppendAllText(directory, "Hello world");
 
         // Overwrites any text already in the file
         StreamWriter writer = new StreamWriter(directory);
         writer.Write("Hello world");
     }

If the file does not exist already, it will be created. Nice.

Saving your data

To save the scriptable objects, it would be good practice to go through every object, save the index of that object in the list, then underneath, save its properties, then leave a space for the next object. Here's an example:

Scriptable object called Item:

 [CreateAssetMenu(fileName = "New Inventory")]
 public class Item : ScriptableObject
 {
     public string Name;
     public int ID;
     public float Price;
     public Vector3 Position;
 }

Class called 'Backpack' with a list of scriptable objects called inventory:

 public class Backpack : MonoBehaviour
 {
     public List<Item> Inventory;
 }

The Save() method would look something like this:

     void SaveInventory(string directory)
     {
         for (int i = 0; i < Inventory.Count; i++)
         {
             Item item = Inventory[i];
 
             File.AppendAllText
             (
                 // Saves object index
                 directory, "Object " + i.ToString() + "\n" +
 
                 // Saves object properties
                 item.name + "\n" +
                 item.ID.ToString() + "\n" +
                 item.Price.ToString() + "\n" +
                 item.Position.ToString() + "\n\n"
             );
         }
     }

And the Load() method would look something like this:

     void LoadInventory(string directory)
     {
         StreamReader reader = new StreamReader(directory);
         string text = reader.ReadToEnd();
 
         // Remember to close the stream IMPORTANT!
         reader.Close();
 
         string[] lines = text.Split('\n');
 
         for (int i = 0; i < lines.Length; i++)
         {
             // Is a new object
             if (lines[i].Contains("Object"))
             {
                 // Get properties
                 string name = lines[i + 1];
                 int id = int.Parse(lines[i + 2]);
                 float price = float.Parse(lines[i + 3]);
                 Vector3 position = StringToVector3(lines[i + 4]);
 
                 // Create new scriptable object and add to inventory
                 Item item = ScriptableObject.CreateInstance<Item>();
 
                 item.Name = name;
                 item.ID = id;
                 item.Price = price;
                 item.Position = position;
 
                 Inventory.Add(item);
             }
         }
     }
 
     Vector3 StringToVector3(string sVector)
     {
         // Remove the parentheses
         if (sVector.StartsWith("(") && sVector.EndsWith(")"))
         {
             sVector = sVector.Substring(1, sVector.Length - 2);
         }
 
         // split the items
         string[] sArray = sVector.Split(',');
 
         // store as a Vector3
         Vector3 result = new Vector3(
             float.Parse(sArray[0]),
             float.Parse(sArray[1]),
             float.Parse(sArray[2]));
 
         return result;
     }

Let me know if this works or not, and I'll try to help. @SaintA721