Improving the ability to drag items, there are still some issues.

改进拖动物品的功能，仍然存在一些问题。

scripts/Config.cs

@@ -170,6 +170,12 @@ public static class Config
     ///<para>在禁用版本隔离时用的</para>
     /// </remarks>
     public const string DefaultVersionName = "Default";
+    
+    /// <summary>
+    /// <para>EmptyVariant</para>
+    /// <para>空变量</para>
+    /// </summary>
+    public static readonly Variant EmptyVariant  = new();
 
 
     /// <summary>
@@ -231,7 +237,13 @@ public static class Config
         /// <para>remove</para>
         /// <para>移除</para>
         /// </summary>
-        Remove
+        Remove,
+        
+        /// <summary>
+        /// <para>Replace</para>
+        /// <para>被替换</para>
+        /// </summary>
+        Replace
     }
 
     public enum OsEnum

scripts/character/CharacterTemplate.cs

@@ -789,7 +789,7 @@ public partial class CharacterTemplate : CharacterBody2D
         {
             return;
         }
-
+        item.ItemContainer = null;
         NodeUtils.CallDeferredAddChild(NodeUtils.FindContainerNode(node2D, GetNode("/root")), node2D);
         switch (item)
         {

scripts/inventory/IItem.cs

@@ -45,6 +45,12 @@ public interface IItem
     /// <para>是否选中</para>
     /// </summary>
     bool IsSelect { get; set; }
+    
+    /// <summary>
+    /// <para>The container in which the item is located</para>
+    /// <para>物品所在的物品容器</para>
+    /// </summary>
+    IItemContainer? ItemContainer { get; set; }
 
     /// <summary>
     /// <para>Calculate how many items can be merged with other items</para>

scripts/inventory/IItemContainer.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Collections.Generic;
 using ColdMint.scripts.map.events;
 
 namespace ColdMint.scripts.inventory;
@@ -76,6 +75,21 @@ public interface IItemContainer
     /// <returns></returns>
     IItem? GetItem(int index);
 
+    /// <summary>
+    /// <para>ReplaceItem</para>
+    /// <para>替换物品</para>
+    /// </summary>
+    /// <remarks>
+    ///<para>Even if the item corresponding to the index is null, it can be successfully replaced.</para>
+    ///<para>即使索引对应的物品为null，也可以成功的替换。</para>
+    /// </remarks>
+    /// <param name="index"></param>
+    /// <param name="item"></param>
+    /// <returns></returns>
+    bool ReplaceItem(int index, IItem item);
+
+    bool ReplaceItem(IItem oldItem, IItem newItem);
+    
     /// <summary>
     /// <para>Gets the item in the specified location, equivalent to <see cref="GetItem"/></para>
     /// <para>获取指定位置的物品，等同于<see cref="GetItem"/></para>
@@ -114,6 +128,14 @@ public interface IItemContainer
     /// </returns>
     int RemoveItem(int itemIndex, int number);
 
+    /// <summary>
+    /// <para>Remove item</para>
+    /// <para>移除物品</para>
+    /// </summary>
+    /// <param name="item"></param>
+    /// <returns></returns>
+    int RemoveItem(IItem item, int number);
+
     /// <summary>
     /// <para>Gets the used capacity of the item container</para>
     /// <para>获取物品容器已使用的容量</para>

scripts/inventory/ItemSlotNode.cs

@@ -32,9 +32,17 @@ public partial class ItemSlotNode : MarginContainer, IItemDisplay
 
     public override Variant _GetDragData(Vector2 atPosition)
     {
+        switch (Item)
+        {
+            case null:
+                return Config.EmptyVariant;
+            case PlaceholderItem:
+                return Config.EmptyVariant;
+        }
+
         if (_iconTextureRect == null)
         {
-            return new Variant();
+            return Config.EmptyVariant;
         }
 
         var textureRect = new TextureRect();
@@ -47,15 +55,25 @@ public partial class ItemSlotNode : MarginContainer, IItemDisplay
 
     public override bool _CanDropData(Vector2 atPosition, Variant data)
     {
-        if (Item == null)
+        var type = data.VariantType;
+        if (type == Variant.Type.Nil)
         {
             return false;
         }
-        if (Item is PlaceholderItem)
+        switch (Item)
         {
-            return false;
+            case null:
+            case PlaceholderItem:
+                return true;
+            default:
+                var itemSlotNode = data.As<ItemSlotNode>();
+                var sourceItem = itemSlotNode.Item;
+                if (sourceItem == null)
+                {
+                    return false;
+                }
+                return Item.MergeableItemCount(sourceItem, sourceItem.Quantity) > 0;
         }
-        return true;
     }
 
     public override void _DropData(Vector2 atPosition, Variant data)
@@ -63,26 +81,21 @@ public partial class ItemSlotNode : MarginContainer, IItemDisplay
         var type = data.VariantType;
         if (type == Variant.Type.Nil)
         {
-            //The passed variable is null.
-            //传入的变量为null。
             return;
         }
         var itemSlotNode = data.As<ItemSlotNode>();
         var sourceItem = itemSlotNode.Item;
         if (sourceItem == null)
         {
-            //Return null when trying to get the source item.
-            //尝试获取源物品时返回null。
             return;
         }
+        if (Item is null || Item is PlaceholderItem)
+        {
+            sourceItem.ItemContainer?.RemoveItem(sourceItem, -1);
+            Item?.ItemContainer?.ReplaceItem(Item, sourceItem);
+        }
     }
 
-    /// <summary>
-    /// <para>Whether to place a backpack in the current slot</para>
-    /// <para>当前槽位是否允许放置背包</para>
-    /// </summary>
-    public bool BackpackAllowed { get; set; }
-
 
     private void UpdateBackground(bool isSelect)
     {

scripts/inventory/PlaceholderItem.cs

@@ -15,6 +15,7 @@ public class PlaceholderItem : IItem
     public int Quantity { get; set; } = 1;
     public int MaxQuantity { get; } = 1;
     public bool IsSelect { get; set; }
+    public IItemContainer? ItemContainer { get; set; }
 
     public int MergeableItemCount(IItem other, int unallocatedQuantity)
     {

scripts/inventory/UniversalItemContainer.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using ColdMint.scripts.debug;
 using ColdMint.scripts.map.events;
 
 namespace ColdMint.scripts.inventory;
@@ -87,7 +86,6 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
         _nextAvailableIndex = UnknownIndex;
         if (totalCapacity <= 0)
         {
-            LogCat.Log("Next available item"+_nextAvailableIndex);
             return;
         }
         for (var i = 0; i < totalCapacity; i++)
@@ -96,7 +94,6 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
             if (!contains)
             {
                 _nextAvailableIndex = i;
-                LogCat.Log("Next available item"+_nextAvailableIndex);
                 return;
             }
         }
@@ -113,6 +110,7 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
 
             var nextAvailableIndex = _nextAvailableIndex;
             _itemDictionary[nextAvailableIndex] = item;
+            item.ItemContainer = this;
             UpdateNextAvailableIndex();
             UpdateSelectStatus(nextAvailableIndex, item);
             ItemDataChangeEvent?.Invoke(new ItemDataChangeEvent
@@ -171,6 +169,7 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
         }
         var finalNextAvailableIndex = _nextAvailableIndex;
         _itemDictionary[finalNextAvailableIndex] = item;
+        item.ItemContainer = this;
         UpdateNextAvailableIndex();
         UpdateSelectStatus(finalNextAvailableIndex, item);
         ItemDataChangeEvent?.Invoke(new ItemDataChangeEvent
@@ -205,6 +204,27 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
         return _itemDictionary.TryGetValue(index, out var item) ? item : null;
     }
 
+    public bool ReplaceItem(int index, IItem item)
+    {
+        var oldItem = GetItem(index);
+        _itemDictionary[index] = item;
+        ItemDataChangeEvent?.Invoke(new ItemDataChangeEvent
+        {
+            NewItem = item,
+            NewIndex = index,
+            OldIndex = index,
+            OldItem = oldItem,
+            Type = Config.ItemDataChangeEventType.Replace
+        });
+        return true;
+    }
+
+    public bool ReplaceItem(IItem oldItem, IItem newItem)
+    {
+        var index = GetIndexByItem(oldItem);
+        return index != UnknownIndex && ReplaceItem(index, newItem);
+    }
+
     public int RemoveSelectItem(int number)
     {
         return RemoveItem(_selectIndex, number);
@@ -221,7 +241,7 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
         {
             return 0;
         }
-        
+
         var originalQuantity = item.Quantity;
         if (number < 0)
         {
@@ -256,6 +276,37 @@ public class UniversalItemContainer(int totalCapacity) : IItemContainer
         return removed;
     }
 
+    public int RemoveItem(IItem item, int number)
+    {
+        var index = GetIndexByItem(item);
+        return index == UnknownIndex ? 0 : RemoveItem(index, number);
+    }
+
+
+    /// <summary>
+    /// <para>Find the corresponding index based on the item object</para>
+    /// <para>根据物品对象查找对应的索引</para>
+    /// </summary>
+    /// <param name="item"></param>
+    /// <returns></returns>
+    private int GetIndexByItem(IItem item)
+    {
+        if (totalCapacity <= 0)
+        {
+            return UnknownIndex;
+        }
+        for (var i = 0; i < totalCapacity; i++)
+        {
+            var contains = _itemDictionary.ContainsKey(i);
+            if (!contains) continue;
+            if (item == _itemDictionary[i])
+            {
+                return i;
+            }
+        }
+        return UnknownIndex;
+    }
+
     public int GetUsedCapacity()
     {
         return _itemDictionary.Count;

scripts/pickable/PickAbleTemplate.cs

@@ -78,6 +78,7 @@ public partial class PickAbleTemplate : RigidBody2D, IItem
 
     public int MaxQuantity { get; set; } = 1;
     public bool IsSelect { get; set; }
+    public IItemContainer? ItemContainer { get; set; }
 
     private Label? _tipLabel;