How to read and write from file in C# UWA (Universal Windows App)

Question

I am trying to figure out how to read and write files in a UWA application. I understand that I need to open a FileStreamm, but I can't figure out how to do that.

I started with this code:

FileStream fs = new FileStream(@"C:\XML\test.txt", FileMode.Create, FileAccess.Write);

seems to work, no red lines.

At the end of all of that I am told to put in Flush and Close, like this:

FileStream fs = new FileStream(@"C:\XML\test.txt", FileMode.Create, 

...

fs.Flush();
fs.Close();

Now, this is where I hit a snag, because fs.Close(); is not even on the list of functions on fs. I just get a red line in my IDE if I try to hardcode it.

Can someone please take the time to help me understand how to do this with UWA? For some reason it seems like there is a different approach in Windows 10 apps, and I have a VERY hard time finding anything that shows me how to do it right. All the tutorials and SOF forum input are about older versions (non-UWA).

When I do this in a console application it all works as expected.

My end goal is to be able to read and write to an XML file in this kind of fashion:

XDocument doc = XDocument.Load(input);
XElement person = doc.Element("Person");
person.Add(new XElement("Employee",
           new XElement("Name", "David"),
           new XElement("Dept", "Chef")));
doc.Save(output);

I'm going down this path because an answer to my previous question told me to use a FileStream, but I simply cannot make that work in UWA.

Answer 1

Okay, the (simple) solution is to put the xml-file in the PROJECTFOLDER/bin/x86/debug/appX and then write the data to a list this way:

public class dataRaw
    {
        public string data { get; set; }
        public string firstName { get; set; }
        public string lastName { get; set; }
    }

    //You can call this class with x = collectionGenerator.getList() (it returns a list<T>)
    public class collectionGenerator
    {
       public static List<dataRaw> getList()
        {
            //This is the xml file in the folder
            var doc = XDocument.Load("Data.xml"); 

            //This parse the XML and adds in to the list "dataList"
            var dataList = doc.Root
                .Descendants("Person")
                .Select(node => new dataRaw
                {
                    //data, firstName and lastName are in app variables from dataRaw put into listData.
                    //Number, FirstName and LastName are the nodes in the XML file.
                    data = node.Element("Number").Value,
                    firstName = node.Element("FirstName").Value,
                    lastName = node.Element("LastName").Value,
                })
            .ToList();
            return dataList;
        }
    }

Answer 2

You cannot just access any file from a Universal Windows App. Access to the file system is restricted.

See the documentation for details.

To help you further we need to know more about your application. What kind of files do you want to access for what reason?

---

Example on how to read an Xml File, modify it and store it in an Universal app. You need a button with the following Click handler and a TextBox named "TextBoxLog".

private async void ButtonDemo_Click(object sender, RoutedEventArgs e)
{
     // Get our local storage folder
     var localFolder = ApplicationData.Current.LocalFolder;

     XmlDocument xmlDocument;

     // Try to get file 
     var file = await localFolder.TryGetItemAsync("MyData.xml") as IStorageFile;

     if(file != null)
     {
          // File exists -> Load into XML document
          xmlDocument = await XmlDocument.LoadFromFileAsync(file);
     }
     else
     {
          // File does not exist, create new document in memory
          xmlDocument = new XmlDocument();
          xmlDocument.LoadXml(@"<?xml version=""1.0"" encoding=""UTF-8""?>" + Environment.NewLine + "<root></root>");
     }

     // Now show the current contents
     TextBoxLog.Text = "";

     var lEntries = xmlDocument.GetElementsByTagName("Entry");
     foreach(var lEntry in lEntries)
     {
          TextBoxLog.Text += lEntry.InnerText + Environment.NewLine;
     }

     // Now add a new entry
     var node = xmlDocument.CreateElement("Entry");
     node.InnerText = DateTime.Now.ToString();
     xmlDocument.DocumentElement.AppendChild(node);

     // If the file does not exist yet, create it
     if(file == null)
     {
          file = await localFolder.CreateFileAsync("MyData.xml");
     }

     // Now save the document
     await xmlDocument.SaveToFileAsync(file);

}