增加项目，分层

Store.Product/Models/Product/MainImageCollection.cs

@@ -0,0 +1,34 @@
+using Store.Product.Models.Product.Image;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Store.Product.Models.Product
+{
+    /// <summary>
+    /// 主图集合
+    /// </summary>
+    public class MainImageCollection : List<ProductImage>
+    {
+        /// <summary>
+        /// 随机排序
+        /// </summary>
+        public void RandomSort()
+        {
+            Random random = new Random();
+            List<ProductImage> newList = new List<ProductImage>();
+            foreach (ProductImage item in this.Take(4))
+            {
+                newList.Insert(random.Next(newList.Count + 1), item);
+            }
+            if (this.Count == 5)
+            {
+                newList.Add(this.Last());
+            }
+            this.Clear();
+            this.AddRange(newList);
+        }
+    }
+}