Inserting new elements in the end of an svg file-CodePudding

I have an svg file in which I would like to insert, say, a circle, using c# and XPath :

This is the file content before:

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="594.75pt" height="841.5pt" viewBox="0 0 594.75 841.5" style="border: 1px solid red">
<circle cx="50%" cy="50%" r="50" fill="red" />
</svg>

I would like this file content after:

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="594.75pt" height="841.5pt" viewBox="0 0 594.75 841.5" style="border: 1px solid red">
<circle cx="50%" cy="50%" r="50" fill="red" />
<circle stroke="blue" stroke-width="3" cx="148.63pt" cy="401.02pt" r="84.15" fill-opacity="0.1"/> 
</svg>

I'm using the following code:

XmlDocument doc = new XmlDocument();
doc.Load(@"D:\\test.svg");

XmlNamespaceManager xmlnsManager = new XmlNamespaceManager(doc.NameTable);
xmlnsManager.AddNamespace("xlink", "http://www.w3.org/1999/xlink");
xmlnsManager.AddNamespace("svg", "http://www.w3.org/2000/svg");

XmlDocumentFragment xmlDocFrag = doc.CreateDocumentFragment();
xmlDocFrag.InnerXml = @"<circle stroke=\"blue\" stroke-width=\"3\" cx=\"148.63pt\" cy=\"401.02pt\" r=\"84.15\" fill-opacity=\"0.1\"/>";

XmlElement mapElement = (XmlElement)doc.SelectSingleNode(@"//svg[last()]", xmlnsManager);
mapElement.AppendChild(xmlDocFrag);  // <----- null !!

doc.Save(path);

However, mapElement is null after SelectSingleNode :( I expected it to be the existing circle element.

CodePudding user response：

The reason you are getting null is because you are not adding the namespace alias defined in xmlnsManager to your XPath.

XmlElement mapElement = (XmlElement)doc.SelectSingleNode(@"//svg:svg[last()]", xmlnsManager);

Or more simply

XmlElement mapElement = (XmlElement)doc.SelectSingleNode(@"/svg:svg", xmlnsManager);

You don't even need XPath at all

XmlElement mapElement = (XmlElement)doc["svg"];

dotnetfiddle

It seems much easier to just use the newer XDocument and XElement classes

var xDoc = XDocument.Load(path);
var xmlns = xDoc.Root.GetDefaultNamespace();
xDoc.Root.Add(new XElement(xmlns   "circle",
                        new XAttribute("stroke","blue"),
                        new XAttribute("stroke-width","3"),
                        new XAttribute("cx","148.63pt"),
                        new XAttribute("cy","401.02pt"),
                        new XAttribute("r","84.15"),
                        new XAttribute("fill-opacity","0.1")
                          )
             );

xDoc.Save(path);

dotnetfiddle