Update lib/src/models/special_item.dart

Co-authored-by: Alex Li <github@alexv525.com>

lib/src/models/special_item.dart

@@ -1,18 +1,20 @@
 import 'package:flutter/material.dart';
 import 'package:wechat_assets_picker/wechat_assets_picker.dart';
 
+/// Allow users to set a special item in the picker grid with specified [position].
+/// 允许用户在选择器中添加一个自定义item，并指定其位置。
 @immutable
-class SpecialItem {
-  SpecialItem({
-    required this.itemPosition,
-    this.itemBuilder,
+class SpecialItem<Path> {
+  const SpecialItem({
+    required this.builder,
+    required this.position,
   });
 
-  /// Allow users set a special item in the picker with several positions.
-  /// 允许用户在选择器中添加一个自定义item，并指定位置
-  final SpecialItemPosition itemPosition;
-
   /// The widget builder for the the special item.
-  /// 自定义item列表
-  final SpecialItemBuilder<AssetPathEntity>? itemBuilder;
+  /// 自定义item构建。
+  final SpecialItemBuilder<Path>? builder;
+
+  /// Define how the item will be positioned.
+  /// 定义如何摆放item。
+  final SpecialItemPosition position;
 }