Unable to update value to XML file in Windows Phone 8

Question

I want to set the attributes pro_id and prod_xml to empty whenever I press on unfavorite icon from the application bar. After all, the values were set to empty, however it also added one more root element to the XML file like this:

<?xml version="1.0" encoding="utf-8"?>
<favorites>
  <favorite id="1" pro_id="" prod_xml="" />
  <favorite id="2" pro_id="" prod_xml="" />
  <favorite id="3" pro_id="" prod_xml="" />
  <favorite id="4" pro_id="" prod_xml="" />
</favorites> />
</favorites>

This is how I create xml file from blank (no error):

public void createFavXML()
{
    // Get the local folder.
    System.IO.IsolatedStorage.IsolatedStorageFile local =
        System.IO.IsolatedStorage.IsolatedStorageFile.GetUserStoreForApplication();

    // Create a new folder named DataFolder.
    if (!local.DirectoryExists("Favorite"))
            local.CreateDirectory("Favorite");
 //       local.DeleteFile("Favorite\\favorite.xml");
        if (!local.FileExists("Favorite\\favorite.xml"))
        {
            // Create a new file named DataFile.txt.
            using (var isoFileStream = 
new System.IO.IsolatedStorage.IsolatedStorageFileStream("Favorite\\Favorite.xml", System.IO.FileMode.OpenOrCreate, local))
        {

            XmlWriterSettings settings = new XmlWriterSettings();
            settings.Indent = true;
            using (XmlWriter writer = XmlWriter.Create(isoFileStream, settings))
            {
                writer.WriteStartElement("favorites", "");
                // favorite id 1
                writer.WriteStartElement("favorite", "");
                // attribute id
                writer.WriteStartAttribute("id", "");
                writer.WriteString("1");
                writer.WriteEndAttribute();
                // attribute product id
                writer.WriteStartAttribute("pro_id", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                // attribute prod_xml
                writer.WriteStartAttribute("prod_xml", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                writer.WriteEndElement();

                // favorite id 2
                writer.WriteStartElement("favorite", "");
                // attribute id
                writer.WriteStartAttribute("id", "");
                writer.WriteString("2");
                writer.WriteEndAttribute();
                // attribute product id
                writer.WriteStartAttribute("pro_id", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                // attribute prod_xml
                writer.WriteStartAttribute("prod_xml", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                writer.WriteEndElement();

                // favorite id 3
                writer.WriteStartElement("favorite", "");
                // attribute id
                writer.WriteStartAttribute("id", "");
                writer.WriteString("3");
                writer.WriteEndAttribute();
                // attribute product id
                writer.WriteStartAttribute("pro_id", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                // attribute prod_xml
                writer.WriteStartAttribute("prod_xml", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                writer.WriteEndElement();

                // favorite id 4
                writer.WriteStartElement("favorite", "");
                // attribute id
                writer.WriteStartAttribute("id", "");
                writer.WriteString("4");
                writer.WriteEndAttribute();
                // attribute product id
                writer.WriteStartAttribute("pro_id", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                // attribute prod_xml
                writer.WriteStartAttribute("prod_xml", "");
                writer.WriteString("");
                writer.WriteEndAttribute();
                writer.WriteEndElement();



                // Ends the document
                writer.WriteEndElement();

                writer.Flush();
            }


        }
    }

}

This is where I write data to xml file for the specific id passed to it (working fine)

   public void writeTOFavxml(string favId,string pro_id,string prod_xml)
    {

        var storage = IsolatedStorageFile.GetUserStoreForApplication();
        fileName = "Favorite\\Favorite.xml";
        using (IsolatedStorageFileStream isoStream = new IsolatedStorageFileStream(fileName, FileMode.Open, storage))
        {

                   XDocument doc = XDocument.Load(isoStream);
                    foreach (var item in (from item in doc.Descendants("favorite")
                                     where item.Attribute("id").Value.Equals(favId)
                                     select item).ToList())
                    {

                        item.Attribute("pro_id").SetValue(pro_id);
                        item.Attribute("prod_xml").SetValue(prod_xml);

                    }                  
                    //First way
                    isoStream.Position = 0;
                    doc.Save(isoStream);                  
                }

    }

After the attributes prod_id and prod_xml have data, I want to be able to set it to be empty again for the specific id that pass to UnwriteXML() method (Problem is here)

public void UnwriteXML(string pro_id)
{
    var storage = IsolatedStorageFile.GetUserStoreForApplication();
    fileName = "Favorite\\Favorite.xml";
    XDocument docx = null;
    using (IsolatedStorageFileStream isoStreamx = new IsolatedStorageFileStream(fileName, FileMode.Open, storage))
    {
        docx = XDocument.Load(isoStreamx);
        foreach (var item in (from item in docx.Descendants("favorite")
                                      where item.Attribute("pro_id").Value.Equals(pro_id)
                                      select item).ToList())
        {
            item.Attribute("pro_id").SetValue("");
            item.Attribute("prod_xml").SetValue("");
        }

        //First way
        isoStreamx.Position = 0;
        docx.Save(isoStreamx);
    }  
}

I followed exactly the same steps as in the question from here updating an existing xml file in Windows Phone by setting isoStream to position 0, because I think he has the same problem as me, but the problem still remains.

Isn't it that you try to overwrite the old xml but since the new one is shorter than the original one you see leftovers at the end of the stream? — Pawel, Sep 29 '14 at 06:38
@har07 from above link I followed the second way is "save XML document in the newly opened stream." `using (var stream = storage.OpenFile(fileName, FileMode.Open, FileAccess.Write)) { doc.Save(stream); }` I've tried both way, but still the same error. — Houy Narun, Sep 29 '14 at 07:04
@Pawel I'm sure I'm not creating new xml overwrite old one. Because as I debug it at UnwriteXML() method and use ISETool.exe to download isolated storage contents, I see in xml file that only one specific id that passed to UnwriteXML() was cleared to be empty, other attributes of `pro_id` and `prod_xml` in other favorite elements still have the same value. Therefore, I think it updated rather than creating new xml. — Houy Narun, Sep 29 '14 at 09:47
@HouyNarun - you are writing to a stream you read from so it looks to me you are overwriting the old xml. You can easily verify this by creating a new stream for the modified document and check if the contents is mangled - I am pretty sure it won't be because the new stream wont have any old data. — Pawel, Sep 29 '14 at 16:49
@Pawel please check my edited question. I could able to create a blank xml file, I could able to write some data for specific id in xml file, however, I met problem when trying to empty the xml after it has data. If I only create it, add data to attributes pro_id and prod_xml and read it works fine, but if I try to empty it, it will create an extra element like above and show error, then I could not read again. — Houy Narun, Sep 30 '14 at 01:48

score 0 · Accepted Answer · answered Sep 30 '14 at 01:46

0

you should set your stream length, this will fix the issue

stream.SetLength(xdoc.ToString().Length);

answered Sep 30 '14 at 01:46

Mahender

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thanks where should I add it? or add it to every method that uses xml file such as CreateFavXML(), WriteToXml() and UnWriteToXML()? – Houy Narun Sep 30 '14 at 04:49
Thanks for answer, I put it after `XDocument.Load(stream)` and it works fine :) – Houy Narun Sep 30 '14 at 05:10
you should put this after resetting the stream position (isoStreamx.Position = 0;) – Mahender Oct 01 '14 at 03:05

Unable to update value to XML file in Windows Phone 8

1 Answers1