Rewriting into xml

Question

I have a listbox and a textbox in my WPF. Im saving these values into an xml like this:

private void textBox1_LostFocus(object sender, RoutedEventArgs e)
{
    if (listBox1.SelectedValue != null)
    {
        writer.WriteStartElement("Attribute",textBox1.Text);
        ListBoxItem a = listBox1.SelectedValue as ListBoxItem;
        if (a != null)
        {
            writer.WriteAttributeString("Name", a.Content.ToString());
        }
        //writer.WriteAttributeString("Value", textBox1.Text);
        writer.WriteEndElement();
        writer.Flush();
    }
}

But when I select an item that is already selected and saved, i want my xml to be re-written. Now i get something like this:

<?xml version="1.0" encoding="utf-8"?>
<Query_advanced>
  <Query>
    <Attribute Name="Patient Name" xmlns="John" />
    <Attribute Name="Patient Age" xmlns="23" />
    <Attribute Name="Patient ID" xmlns="12" />
    <Attribute Name="Patient Name" xmlns="Mary" />
  </Query>
</Query_advanced>

How can I go about this? Thanks!

Answer 1

Taking @bitbonk's answer answer into account and modifying, this worked for me:

private void textBox1_LostFocus(object sender, RoutedEventArgs e){
    if (listBox2.SelectedValue != null){
         string name = listBox2.SelectedItem.ToString();
         string value = textBox1.Text;
         if(!attributes_dict.ContainsKey(name)){
             //attributes.Add(name, value);
             attributes_dict[name] = value;
             //UpdateXml();
         }else{
             attributes_dict.Remove(name);
             attributes_dict.Add(name, value);
             //UpdateXml();
         }
     }
}


private  void button1_Click(object sender, RoutedEventArgs e){
     foreach (KeyValuePair<string, string> attribute in this.attributes_dict){
          writer.WriteStartElement("Attribute", textBox1.Text);
          if(attribute.Key != null){
               writer.WriteAttributeString("Name1", attribute.Key);
          }
          writer.WriteAttributeString("Value1", attribute.Value);                                     
          writer.WriteEndElement();
     }
     writer.Flush();
     writer.WriteEndElement();
     writer.Flush();
     writer.WriteEndDocument();
     writer.Close();
}