Use XmlWriter rather than XmlTextWriter (#824)

* handle the element namespace directly as a property of an element, 
  rather than adding it to the collection of attributes
* use XmlWriter rather than XmlTextWriter (see #693)
* explicitly call XmlWriter.Flush()
* add XmlDoc recommendation on XmlWriter usage
* closes #693

Author: xprl-gjf

Source/Metadata/SvgDocumentMetadata.cs

@@ -25,7 +25,7 @@ protected override void Render(ISvgRenderer renderer)
             // Do nothing. Children should NOT be rendered.
         }
 
-        protected override void WriteChildren(XmlTextWriter writer)
+        protected override void WriteChildren(XmlWriter writer)
         {
             writer.WriteRaw(this.Content); // write out metadata as is
         }

Source/Scripting/SvgScript.cs

@@ -1,4 +1,4 @@
-using System.Xml;
+using System.Xml;
 
 namespace Svg
 {
@@ -41,7 +41,7 @@ public override SvgElement DeepCopy()
             return DeepCopy<SvgScript>();
         }
 
-        protected override void WriteChildren(XmlTextWriter writer)
+        protected override void WriteChildren(XmlWriter writer)
         {
             if (!string.IsNullOrEmpty(Content))
             {

Source/SvgDocument.cs

@@ -723,7 +723,7 @@ public virtual void RasterizeDimensions(ref SizeF size, int rasterWidth, int ras
             }
         }
 
-        public override void Write(XmlTextWriter writer)
+        public override void Write(XmlWriter writer)
         {
             //Save previous culture and switch to invariant for writing
             var previousCulture = Thread.CurrentThread.CurrentCulture;
@@ -742,11 +742,13 @@ public override void Write(XmlTextWriter writer)
 
         public void Write(Stream stream, bool useBom = true)
         {
-
-            var xmlWriter = new XmlTextWriter(stream, useBom ? Encoding.UTF8 : new UTF8Encoding(false))
+            var settings = new XmlWriterSettings
             {
-                Formatting = Formatting.Indented
+                Encoding = useBom ? Encoding.UTF8 : new System.Text.UTF8Encoding(false),
+                Indent = true
             };
+
+            using var xmlWriter = XmlWriter.Create(stream, settings);
             xmlWriter.WriteStartDocument();
             xmlWriter.WriteDocType("svg", "-//W3C//DTD SVG 1.1//EN", "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd", null);
 
@@ -766,7 +768,7 @@ public void Write(string path, bool useBom = true)
             }
         }
 
-        protected override void WriteStartElement(XmlTextWriter writer)
+        protected override void WriteStartElement(XmlWriter writer)
         {
             base.WriteStartElement(writer);
 

Source/SvgElement.cs

@@ -589,7 +589,7 @@ public virtual bool ShouldWriteElement()
             return !string.IsNullOrEmpty(this.ElementName);
         }
 
-        protected virtual void WriteStartElement(XmlTextWriter writer)
+        protected virtual void WriteStartElement(XmlWriter writer)
         {
             if (!string.IsNullOrEmpty(this.ElementName))
             {
@@ -599,14 +599,14 @@ protected virtual void WriteStartElement(XmlTextWriter writer)
             this.WriteAttributes(writer);
         }
 
-        protected virtual void WriteEndElement(XmlTextWriter writer)
+        protected virtual void WriteEndElement(XmlWriter writer)
         {
             if (!string.IsNullOrEmpty(this.ElementName))
             {
                 writer.WriteEndElement();
             }
         }
-        protected virtual void WriteAttributes(XmlTextWriter writer)
+        protected virtual void WriteAttributes(XmlWriter writer)
         {
             //properties
             var styles = WritePropertyAttributes(writer);
@@ -662,7 +662,7 @@ protected virtual void WriteAttributes(XmlTextWriter writer)
             }
         }
 
-        private Dictionary<string, string> WritePropertyAttributes(XmlTextWriter writer)
+        private Dictionary<string, string> WritePropertyAttributes(XmlWriter writer)
         {
             var styles = _styles.ToDictionary(_styles => _styles.Key, _styles => _styles.Value.Last().Value);
 
@@ -956,7 +956,20 @@ private bool TryResolveParentAttributeValue(string attributeKey, out object pare
             return resolved;
         }
 
-        public virtual void Write(XmlTextWriter writer)
+        /// <summary>
+        /// Write this SvgElement out using a given XmlWriter.
+        /// </summary>
+        /// <param name="writer">The XmlWriter to use.</param>
+        /// <remarks>
+        /// Recommendation is to create an XmlWriter by calling a factory method,<br/>
+        /// e.g. <see cref="XmlWriter.Create(System.IO.Stream)"/>,
+        /// as per <a href="https://docs.microsoft.com/dotnet/api/system.xml.xmltextreader#remarks">Microsoft documentation</a>.<br/>
+        /// <br/>
+        /// However, unlike an <see cref="XmlTextWriter"/> created via 'new XmlTextWriter()',<br/>
+        /// a factory-constructed XmlWriter will not flush output until it is closed<br/>
+        /// (normally via a using statement), or unless the client explicitly calls <see cref="XmlWriter.Flush()"/>.
+        /// </remarks>
+        public virtual void Write(XmlWriter writer)
         {
             if (ShouldWriteElement())
             {
@@ -966,7 +979,7 @@ public virtual void Write(XmlTextWriter writer)
             }
         }
 
-        protected virtual void WriteChildren(XmlTextWriter writer)
+        protected virtual void WriteChildren(XmlWriter writer)
         {
             if (this.Nodes.Any())
             {

Source/SvgExtentions.cs

@@ -50,12 +50,14 @@ public static string GetXML(this SvgElement elem)
             try
             {
                 Thread.CurrentThread.CurrentCulture = CultureInfo.InvariantCulture;
-                using (var str = new StringWriter())
-                using (var xml = new XmlTextWriter(str))
-                {
-                    elem.Write(xml);
-                    result = str.ToString();
-                }
+
+                var writerSettings = new XmlWriterSettings { Encoding = System.Text.Encoding.UTF8 };
+
+                using var str = new StringWriter();
+                using var xml = XmlWriter.Create(str, writerSettings);
+                elem.Write(xml);
+                xml.Flush();
+                result = str.ToString();
             }
             finally
             {