另一个空引用异常

Question

我知道空引用异常通常总是模糊的，任何数量的东西都可以产生它，但我在这里没有想法了......发生的事情是当我尝试单击食谱类别链接时我收到此错误：

NullReferenceException: Object reference not set to an instance of an object.
Company.BusinessLayer.Recipes.SearchManager.GetRecipes(Int64 folderId, String searchTerm, Int32 pageIndex, Int32 pageSize, Int32& categoryCount, Int32& pageCount) +1020
TargetInvocationException: Exception has been thrown by the target of an invocation.
Comapny.Website.Controls.Recipes.CategoryControl.ods_Selected(Object sender, ObjectDataSourceStatusEventArgs e) +940


System.Web.UI.WebControls.ObjectDataSourceView.OnSelected(ObjectDataSourceStatusEventArgs e) +103
   System.Web.UI.WebControls.ObjectDataSourceView.InvokeMethod(ObjectDataSourceMethod method, Boolean disposeInstance, Object& instance) +431
   System.Web.UI.WebControls.ObjectDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments) +1953
   System.Web.UI.WebControls.BaseDataList.GetData() +56
   System.Web.UI.WebControls.DataList.CreateControlHierarchy(Boolean useDataSource) +177
   System.Web.UI.WebControls.BaseDataList.OnDataBinding(EventArgs e) +64
   System.Web.UI.WebControls.BaseDataList.DataBind() +55
   Company.Website.Controls.Recipes.CategoryControl.OnPreRender(EventArgs e) +138
   System.Web.UI.Control.PreRenderRecursiveInternal() +103
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Control.PreRenderRecursiveInternal() +175
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2496

我不能但不知道什么被处理为空。以下是来自 SearchManager.cs 的代码以及错误消息引用的 GetRecipes 方法。数据全部存在于数据库中，任何内容都不应该为空。在我升级该项目所依赖的程序集之前，它曾经一度工作过。唯一改变的是程序集使用 int64 而不是 int，但为了构建该死的项目，我必须将它们转换为 int。但在这种情况下我想这应该不重要。我不知道我在这里抓住了空气。

public ContentBase[] GetRecipes(long folderId, string searchTerm, int pageIndex, int pageSize, out int categoryCount, out int pageCount)
{
    ContentBase[] mergedResultset = null;

    IndexSearch idx = new IndexSearch();

    idx.XmlConfigId = 8;
    idx.FolderId = folderId;
    idx.Recursive = true;


    // if a search term is provided, search this term
    if (!string.IsNullOrEmpty(searchTerm))
    {
        searchTerm = searchTerm.Replace("'", "''");

        // INDEX SEARCH BASED ON INGREDIENTS
        Ektron.Cms.Controls.IndexSearch.SearchPram paramTerm = new Ektron.Cms.Controls.IndexSearch.SearchPram();
        paramTerm.DataType = Ektron.Cms.Common.EkEnumeration.XMLDataType.String;
        paramTerm.SearchType = Ektron.Cms.Common.EkEnumeration.XMLSearchRangeType.Contains;
        paramTerm.XPath = "/root/Ingredients";
        paramTerm.Value1 = searchTerm;
        idx.AddParm(paramTerm);

        idx.Search();
        mergedResultset = (ContentBase[])idx.EkItems;

        // CUSTOM SEARCH BASED ON TITLE
        FolderData[] childFolders = GetChildFolders(folderId, true);

        // Search based on title
        Ektron.Cms.API.Search.SearchManager search = new Ektron.Cms.API.Search.SearchManager();
        Ektron.Cms.ContentSearchCondition conditionAll = new Ektron.Cms.ContentSearchCondition();
        conditionAll.setType = EkEnumeration.SearchType.AND;

        ContentSearchCondition condFolderIds = new ContentSearchCondition();
        // add condition folder Id for current folder and for each sub folder
        condFolderIds.setType = EkEnumeration.SearchType.OR;
        AddFolderIdCondition(condFolderIds, folderId);
        foreach (FolderData fd in childFolders)
        {
            AddFolderIdCondition(condFolderIds, fd.Id);
        }
        conditionAll.AddCondition(condFolderIds);

        ContentSearchCondition condTerm = new ContentSearchCondition();
        condTerm.setType = EkEnumeration.SearchType.LIKE;
        condTerm.setValue = searchTerm;
        condTerm.setVariable = "content.content_title";
        conditionAll.AddCondition(condTerm);

        ContentSearchCondition condType = new ContentSearchCondition();
        condType.setType = EkEnumeration.SearchType.EQUAL;
        condType.setValue = 8;
        condType.setVariable = "content.xml_config_id";
        conditionAll.AddCondition(condType);

        ContentData[] contents = search.Execute(conditionAll);


        mergedResultset = MergeResultsets(idx.EkItems, contents, "/Recipes/Detail.aspx");

        // rewrite all quicklinks with url alias
        IDictionary<int, string> aliases = new UrlAliasApi().GetUrlAliasesByType(Company.DataLayer.Enumeration.UrlAliasType.Recipe);
        foreach (ContentBase recipe in mergedResultset)
        {
            // if alias exists, overwrite quicklink!
            string alias;
            if (aliases.TryGetValue((int)recipe.Id, out alias))
            {
                recipe.QuickLink = alias;
            }
        }

    }
        // otherwise search based without parameter (fake param)
    else
    {
        // if category recipes not already in cache, get them through ektron, otherwise, just get them from cache
        if (RecipeCategoryCache.Current.Categories.ContainsKey((int)folderId) && RecipeCategoryCache.Current.Categories[(int)folderId] != null && RecipeCategoryCache.Current.Categories[(int)folderId].Length > 0)
        {
            mergedResultset = RecipeCategoryCache.Current.Categories[(int)folderId];
        }
        else
        {
            Ektron.Cms.Controls.IndexSearch.SearchPram param = new Ektron.Cms.Controls.IndexSearch.SearchPram();
            param.DataType = Ektron.Cms.Common.EkEnumeration.XMLDataType.Boolean;
            param.SearchType = Ektron.Cms.Common.EkEnumeration.XMLSearchRangeType.True;
            param.XPath = "/root/Viewable";
            idx.AddParm(param);

            idx.Search();
            mergedResultset = (ContentBase[])idx.EkItems;

            // rewrite all quicklinks with url alias
            IDictionary<int, string> aliases = new UrlAliasApi().GetUrlAliasesByType(Company.DataLayer.Enumeration.UrlAliasType.Recipe);
            foreach (ContentBase recipe in mergedResultset)
            {
                // if alias exists, overwrite quicklink!
                string alias;
                if (aliases.TryGetValue((int)recipe.Id, out alias))
                {
                    recipe.QuickLink = alias;
                }
            }

            RecipeCategoryCache.Current.Categories[(int)folderId] = mergedResultset;
        }
    }

    categoryCount = mergedResultset.Length;

    // if page size provided is 0, No paging,
    // if more than 0, calculate paging
    if (pageSize > 0 && mergedResultset.Length > 0)
    {
        PagingHelper pgHelper = new PagingHelper();
        pgHelper.CalculatePagingInfo(pageIndex, categoryCount, pageSize);

        pageCount = pgHelper.NumberOfPages;

        List<ContentBase> lst = new List<ContentBase>();

        for (int i = pgHelper.StartIndex; i < pgHelper.EndIndex; i++)
        {
            lst.Add(mergedResultset[i]);
        }

        return lst.ToArray();

    }
    else
    {
        pageCount = 1;
        return mergedResultset;
    }

}

Answer 1

您需要添加大量错误处理代码。没有单一的“if (x != null)”或“if (x == null)”类型的语句。您需要重写所有代码以更具防御性。

是的，要找到这个特定的错误，您需要单步调试您的程序。看看它在哪里爆炸。但是如果你解决了这个问题，除非你添加了大量的错误检查代码，否则无法保证你的代码不会在 5 分钟后在其他地方崩溃。

看起来您正在整个方法中调用外部代码。基本上，您需要验证从中返回的所有内容，看起来您相信外部代码始终返回有效数据。

Answer 2

如果不在那里并能够深入研究您的代码，这几乎是不可能的。我可以告诉您要做的是查找为空的子对象。例如，假设您有一个 Car 对象：

class Car(){
string Color;
string Make;
string Model;
Passenger passenger; // Passenger is a another object defined elsewhere
}

在代码中的某个时刻，您执行类似...

Car car = new Car(); 的

操作然后你去某个地方使用它，在你的代码中，有些东西尝试访问 Passenger 的属性，但 Passenger 是 NULL。问题是，在更高的层面上，当你查看 Car 时，你会看到 car 不为空，所以你认为它没问题。理解？

所以...检查你的复杂对象是否有空值，看看它在哪里。顺便说一句，如果您在代码中尝试...catch 广泛定义的语句，它们会非常好地导致这种错误并使其很难找到...

Answer 3

为什么不在函数顶部设置一个中断并逐步调试并检查变量呢？这是找出空引用异常原因的最简单方法。