Question

我有一个非常奇怪的空引用异常，它阻止了我的进展。

我正在制作一本书。每本书都有页面，每个页面都可以有文本项和图像。我试图将这些对象保存在Xml文件中。我第一次保存对象一切顺利。 Xml由c＃创建，加载，填充并保存。当我尝试向书中添加/保存新页面时，我无法获取已存在的Xml文件。问题是我的代码永远不会达到我可以读取文件的程度。当我创建一个空的XDocument对象时，它会出错。错误说＆＃34; documentType是一个空引用＆＃34;。

第一次调用create方法是我保存第一页的第一组对象。我没有收到任何错误，Xml被正确保存。但是当我再次尝试保存（新页面或当前页面）时，我收到错误（图片底部的帖子）。

调试器在XDocument doc之后停止; （在LoadXml中）然后抛出图像中显示的NullReferenceException。 通过向XML添加XDocumentType节点来解决此问题。

新错误： 新错误表明XDocument的Root是一个空引用。在DocumentType给出错误之前。

加载Xml

/// <summary>
/// Loads the XML file for the given path.
/// A new document will be created if the file does not exist or is corrupted.
/// </summary>
/// <param name="collectionId">The collectionId to load the file from.</param>
/// <param name="newFile">A boolean result which states if the returned file is new.</param>
/// <returns>The requested file or a new one.</returns>
public static XDocument LoadXml(int collectionId, int version, out bool newFile, CollectionType collectionType)
{
    newFile = false;
    XDocument doc; // Here I get the error when I run the code for a second time

    string file = GetXmlPath(collectionId, collectionType, version) + "/photobook.xml";

    if (System.IO.File.Exists(file))
    {
        try
        {
            doc = XDocument.Load(file);
        }
        catch
        {
            newFile = true;
            doc = CreateNewXml();
        }
    }
    else
    {
        newFile = true;
        doc = CreateNewXml();
    }

    return doc;
}

SaveNewPage

/// <summary>
/// Add and save a new page to an existing book. 
/// </summary>
/// <param name="pageInfoParam">New pageInfo object that has to be added to the collection.</param>
/// <param name="collectionId">Id of the collection which is being edited.</param>
/// <param name="version">Version of the collection which is being edited.</param>
/// <returns>True if succesful.</returns>
public static bool SaveNewPageInfo(PageInfo pageInfoParam, int collectionId, int version)
{

    bool result = false;
    // Make sure the collection exists
    if (!CollectionExists(collectionId, version))
    {
        Logger.log("Error: Collection {0} not found.", collectionId);
        throw new Exception("Fotoboek niet gevonden.");
    }

    Logger.log("Saving page info...");

    bool newFile;
    XDocument doc = XmlService.LoadXml(collectionId, version, out newFile, CollectionType.collection);

    if (!newFile)
    {
        // This should never happen, we just successfully saved the XML
        result = false;
        Logger.log("Xml could not be loaded when trying to save a new page.");
        throw new Exception("Fout bij het opslaan van de nieuwe pagina.");
    }

    // Get all current pages from the document.
    List<XElement> pages = doc.Root.Element("inner").Elements("page").ToList();

    #region New page in new book
    // If no pages available we have to add a new page element.

    #endregion

    #region Edit existing page in book
    // If pages exist find the page we edited, remove all text and add the new text.

    #endregion

    // Try to save the XML file
    if (!XmlService.SaveXml(doc, collectionId, version))
    {
        Logger.log("Xml could not be saved.");
        throw new Exception("De pagina kon niet worden opgeslagen.");
    }
    else
    {
        Logger.log("Page info for collection {0} saved successfully in Xml.", collectionId);
        result = true;
        return result;
    }
}

XML

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE Book SYSTEM "Book.dtd"> 
<album version="0.2" settingsVersion="1">   
    <size />   
    <cover />   
    <inner>
       <page>
           <pagenumber>1</pagenumber>
           <image>04.jpg</image>
           <textelements>
             <text>
               <value>Test </value>
               <font>arial</font>
               <size>18pt</size>
               <style>normal</style>
               <weight>normal</weight>
               <color>#77DD44</color>
               <rotation>0</rotation>
               <alignment>start</alignment>
               <position>
                   <x>50</x>
                   <y>50</y>
               </position>
             </text>
          </textelements>
        </page> 
    </inner> 
 </album>

lower_bound().

XDocument documentType null引用

0 个答案: