记一次线上报错 GList AddChildAt NullReferenceException

文章目录

- 问题描述
- 分析
- 结果
- 总结

问题描述

后台日志大量报错，去主干看无法复现
c# exception:System.NullReferenceException: Object reference not set to an instance of an object. at FairyGUI.GCompone
nt.AddChildAt (FairyGUI.GObject child, System.Int32 index) [0x00000] in <00000000000000000000000000000000>:0 at Fairy
GUI.GList.AddChildAt (FairyGUI.GObject child, System.Int32 index) [0x00000] in <00000000000000000000000000000000>:0 a
t FairyGUI.GComponent.AddChild (FairyGUI.GObject child) [0x00000] in <00000000000000000000000000000000>:0 at FairyGUI
.GList.set_numItems…

分析

看逻辑是没有问题的，但是在调用numItems时c#层报错。看FairyGUI的代码，

public int numItems
{get{if (_virtual)return _numItems;elsereturn _children.Count;}set{if (_virtual){if (itemRenderer == null)throw new Exception("FairyGUI: Set itemRenderer first!");_numItems = value;if (_loop)_realNumItems = _numItems * 6;//设置6倍数量，用于循环滚动else_realNumItems = _numItems;//_virtualItems的设计是只增不减的int oldCount = _virtualItems.Count;if (_realNumItems > oldCount){for (int i = oldCount; i < _realNumItems; i++){ItemInfo ii = new ItemInfo();ii.size = _itemSize;_virtualItems.Add(ii);}}else{for (int i = _realNumItems; i < oldCount; i++)_virtualItems[i].selected = false;}if (_virtualListChanged != 0)Timers.inst.Remove(this.RefreshVirtualList);//立即刷新this.RefreshVirtualList(null);}else{int cnt = _children.Count;if (value > cnt){for (int i = cnt; i < value; i++){if (itemProvider == null)AddItemFromPool();elseAddItemFromPool(itemProvider(i));}}else{RemoveChildrenToPool(value, cnt);}if (itemRenderer != null){for (int i = 0; i < value; i++)itemRenderer(i, GetChildAt(i));}}}
}

AddChild 发生在 AddItemFromPool 中

/// <summary>
/// Add a item to list, same as GetFromPool+AddChild
/// </summary>
/// <returns>Item object</returns>
public GObject AddItemFromPool()
{GObject obj = GetFromPool(null);return AddChild(obj);
}/// <summary>
/// Add a item to list, same as GetFromPool+AddChild
/// </summary>
/// <param name="url">Item resource url</param>
/// <returns>Item object</returns>
public GObject AddItemFromPool(string url)
{GObject obj = GetFromPool(url);return AddChild(obj);
}

AddChild 的参数为空引用，看GetFromPool如何拿到

public GObject GetFromPool(string url)
{if (string.IsNullOrEmpty(url))url = _defaultItem;GObject ret = _pool.GetObject(url);if (ret != null)ret.visible = true;return ret;
}

最终定位到GObjectPool.GetObject,对象是从对象池池子中取出的，没取到则创建一个

        public GObject GetObject(string url){url = UIPackage.NormalizeURL(url);if (url == null)return null;Queue<GObject> arr;if (_pool.TryGetValue(url, out arr)&& arr.Count > 0)return arr.Dequeue();GObject obj = UIPackage.CreateObjectFromURL(url);if (obj != null){if (initCallback != null)initCallback(obj);}return obj;}

从上面的代码可以得出报错的原因

可能池子里拿出来的对象在lua层已经被销毁了
可能创建对象没有成功，资源存在问题

在lua代码报错的地方加入以下定位代码

    local list = self._listviewlocal obj, nullNum, lossNumfor i = list.numChildren + 1, infoLen do -- 先处理已经销毁了的obj, nullNum, lossNum = self:getItmeFromPool(list)if obj thenlist:AddChild(obj)elseif SDKCtrl thenSDKCtrl:reportError(" warning 上报定位  get null tiems:" .. nullNum .. "  get Disposed times: " .. lossNum)endendendlist.numItems = infoLenlist:ResizeToFit(infoLen)

function mod:getItmeFromPool(list)local objlocal lossNum, nullNum = 0, 0while lossNum < 100 and nullNum < 100 doobj = list:GetFromPool()if not obj thennullNum = nullNum + 1elseif obj.isDisposed thenlossNum = lossNum + 1elsebreakendendreturn obj, nullNum, lossNum
end