UnitySerializedReferenceUI/Editor/Attributes/SerializeReferenceButtonAttributeDrawer.cs

#if UNITY_EDITOR
using System;
using System.Collections.Generic;
using UnityEditor; 
using UnityEngine;

[CustomPropertyDrawer(typeof(SerializeReferenceButtonAttribute))]
public class SerializeReferenceButtonAttributeDrawer : PropertyDrawer
{
    public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
    {
        return EditorGUI.GetPropertyHeight(property, true);
    }
 
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {    
        EditorGUI.BeginProperty(position, label, property);

        Rect labelPosition = new Rect(position.x, position.y, position.width, EditorGUIUtility.singleLineHeight);
        EditorGUI.LabelField(labelPosition, label);

        IEnumerable<Func<Type, bool>> typeRestrictions = SerializedReferenceUIDefaultTypeRestrictions.GetAllBuiltInTypeRestrictions(fieldInfo);
        property.DrawSelectionButtonForManagedReference(position, typeRestrictions);
        
        EditorGUI.PropertyField(position, property, GUIContent.none, true);
        
        EditorGUI.EndProperty(); 
    } 
}
#endif