XDocument保存有什么问题？

Question

I am trying to save some changes back to an XML file using Linq and I have seen many examples on SO and tutorial sites doing it like this but for some reason I am getting an error on the xmlDoc.Save(customerXMLPath); line Argument 1: cannot convert from 'string' to 'System.IO.Stream' .

Most of the samples I have seen are ASP.Net samples but I wouldn't think that should make much a difference on the syntax (this is a UWP app). Can someone please tell me what I am doing wrong?

private void SaveChange_Click(object sender, RoutedEventArgs e)
{
    string customerXMLPath = 
        Path.Combine(Package.Current.InstalledLocation.Path, "XML/Customers.xml");

    XDocument xmlDoc = XDocument.Load(customerXMLPath);

    var updateQuery = from r in xmlDoc.Descendants("Customer")
                      where r.Element("CustomerId").Value == txtCustomerId.Text
                      select r;

    foreach (var query in updateQuery)
    {
        query.Element("State").SetValue(txtState.Text);
    }

    xmlDoc.Save(customerXMLPath);
}

Edit: according to the comments there is no overload for Save in UWP. So does that mean (based on another comment) that I have to save as a stream? If that is the case wouldn't I have to overwrite the file? <-- that doesn't make sense when I am just trying to change a few values but maybe I misunderstood the answer.

My assumption is that there is a way to update a XML file in UWP so am I just going about this all wrong? What is the recommended way? By the way SQLite is not an option right now because the files have to remain in XML format

Answer 1

Instead of using your own "slash" mark in the Path.Combine statement, let it do that for you. So you know your path is acceptable to the operating system you are using.

Switch this:

string customerXMLPath = 
        Path.Combine(Package.Current.InstalledLocation.Path, "XML/Customers.xml");

To this:

string customerXMLPath = 
        Path.Combine(Package.Current.InstalledLocation.Path, "XML", "Customers.xml");

But that isn't necessarily your problem. It appears you are trying to write to a READ ONLY location. See this post for more . I'll quote the text portion of the answer here.

...the problem is we cannot update file content of the installation folder, this folder a read-only one, so the workaround is to place your xml file in the folder which we have both read and write rights...

Answer 2

I think I might have found a solution for this, but it involves overriding files. It might be dirty, but it works for me.

I created a xml file in the ApplicationData.Current.LocalFolder.Path location. Working in the install directory (Package.Current.InstalledLocation.Path) can be difficult since all the files in there are sand-boxed, you will not have permissions to modify them.

So the first section will look something like this.

string customerXMLPath = 
Path.Combine(ApplicationData.Current.LocalFolder.Path, "XML/Customers.xml");

After that you can run your XDocument code. But don't bother calling xmlDoc.Save(customerXMLPath) because that won't work in a UWP app.

So the second section will look something like this. Like you have already.

XDocument xmlDoc = XDocument.Load(customerXMLPath);

var updateQuery = from r in xmlDoc.Descendants("Customer")
                  where r.Element("CustomerId").Value == txtCustomerId.Text
                  select r;

foreach (var query in updateQuery)
{
    query.Element("State").SetValue(txtState.Text);
}

The last part is where you would have to save the contents of your XDocument to the file, overriding any content already in the file. Since this is an await operation, it would be advised that you make your method async as well. StorageFolder and StorageFile should be used to get the location and file recreation.

So the last part would look something like this.

StorageFolder storageFolder = ApplicationData.Current.LocalFolder;                
var newfile = await storageFolder.CreateFileAsync("Customers.xml",
CreationCollisionOption.ReplaceExisting);

await FileIO.WriteTextAsync(newfile, xmlDoc.ToString());

So the full example will look like this.

using System.Xml.Linq;
using Windows.Storage;
using System.IO;
using System.Linq;

private void cmdStart_Click(object sender, RoutedEventArgs e)
{
    SaveXml();
}

private async void SaveXml()
{
   string XML_DATA_FILE = "Customer.xml";
   string customerXMLPath = Path.Combine(ApplicationData.Current.LocalFolder.Path, XML_DATA_FILE);

    if (File.Exists(xmlPath))
    {             

      XDocument xmlDoc = XDocument.Load(customerXMLPath);

      var updateQuery = from r in xmlDoc.Descendants("Customer")
                  where r.Element("CustomerId").Value == txtCustomerId.Text
                  select r;

     foreach (var query in updateQuery)
     {
         query.Element("State").SetValue(txtState.Text);
     }                             

     StorageFolder storageFolder = ApplicationData.Current.LocalFolder;                
     var newfile = await storageFolder.CreateFileAsync(XML_DATA_FILE, 
     CreationCollisionOption.ReplaceExisting);

     await FileIO.WriteTextAsync(newfile, xmlDoc.ToString());                
    }            
}

I hope this helps and gives some guidance.

Cheers.