Refactor using an extension method (LINQ to XML)

This example builds on the previous example, Retrieve the text of the paragraphs, by refactoring the concatenation of strings using a pure function that's implemented as an extension method.

The previous example used the Aggregate standard query operator to concatenate multiple strings into one string. However, it's more convenient to write an extension method to do this, because the resulting query is smaller and simpler.

Example: Retrieve the paragraphs, their styles, and their text

This example processes a WordprocessingML document, retrieving the paragraphs and the style and text for each paragraph. This example builds on the previous examples in this tutorial.

The example contains multiple overloads of the StringConcatenate method.

The instructions for creating the source document for this example are in Create the source Office Open XML document.

This example uses classes from the WindowsBase assembly. It uses types in the System.IO.Packaging namespace.

public static class LocalExtensions
{
    public static string StringConcatenate(this IEnumerable<string> source)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string s in source)
            sb.Append(s);
        return sb.ToString();
    }

    public static string StringConcatenate<T>(this IEnumerable<T> source,
        Func<T, string> func)
    {
        StringBuilder sb = new StringBuilder();
        foreach (T item in source)
            sb.Append(func(item));
        return sb.ToString();
    }

    public static string StringConcatenate(this IEnumerable<string> source, string separator)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string s in source)
            sb.Append(s).Append(separator);
        return sb.ToString();
    }

    public static string StringConcatenate<T>(this IEnumerable<T> source,
        Func<T, string> func, string separator)
    {
        StringBuilder sb = new StringBuilder();
        foreach (T item in source)
            sb.Append(func(item)).Append(separator);
        return sb.ToString();
    }
}

Example: Use all four overloads of the StringConcatenate method

There are four overloads of the StringConcatenate method. One overload simply takes a collection of strings and returns a single string. Another overload can take a collection of any type, and a delegate that projects from a singleton of the collection to a string. There are two more overloads that allow you to specify a separator string.

The following code uses all four overloads:

string[] numbers = { "one", "two", "three" };

Console.WriteLine("{0}", numbers.StringConcatenate());
Console.WriteLine("{0}", numbers.StringConcatenate(":"));

int[] intNumbers = { 1, 2, 3 };
Console.WriteLine("{0}", intNumbers.StringConcatenate(i => i.ToString()));
Console.WriteLine("{0}", intNumbers.StringConcatenate(i => i.ToString(), ":"));

This example produces the following output:

onetwothree
one:two:three:
123
1:2:3:

Example: Use the new extension method

Now the example can be modified to take advantage of the new extension method:

public static class LocalExtensions
{
    public static string StringConcatenate(this IEnumerable<string> source)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string s in source)
            sb.Append(s);
        return sb.ToString();
    }

    public static string StringConcatenate<T>(this IEnumerable<T> source,
        Func<T, string> func)
    {
        StringBuilder sb = new StringBuilder();
        foreach (T item in source)
            sb.Append(func(item));
        return sb.ToString();
    }

    public static string StringConcatenate(this IEnumerable<string> source, string separator)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string s in source)
            sb.Append(s).Append(separator);
        return sb.ToString();
    }

    public static string StringConcatenate<T>(this IEnumerable<T> source,
        Func<T, string> func, string separator)
    {
        StringBuilder sb = new StringBuilder();
        foreach (T item in source)
            sb.Append(func(item)).Append(separator);
        return sb.ToString();
    }
}

class Program
{
    static void Main(string[] args)
    {
        const string fileName = "SampleDoc.docx";

        const string documentRelationshipType =
          "http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument";
        const string stylesRelationshipType =
          "http://schemas.openxmlformats.org/officeDocument/2006/relationships/styles";
        const string wordmlNamespace =
          "http://schemas.openxmlformats.org/wordprocessingml/2006/main";
        XNamespace w = wordmlNamespace;

        XDocument xDoc = null;
        XDocument styleDoc = null;

        using (Package wdPackage = Package.Open(fileName, FileMode.Open, FileAccess.Read))
        {
            PackageRelationship docPackageRelationship =
              wdPackage.GetRelationshipsByType(documentRelationshipType).FirstOrDefault();
            if (docPackageRelationship != null)
            {
                Uri documentUri = PackUriHelper.ResolvePartUri(new Uri("/", UriKind.Relative),
                  docPackageRelationship.TargetUri);
                PackagePart documentPart = wdPackage.GetPart(documentUri);

                //  Load the document XML in the part into an XDocument instance.
                xDoc = XDocument.Load(XmlReader.Create(documentPart.GetStream()));

                //  Find the styles part. There will only be one.
                PackageRelationship styleRelation =
                  documentPart.GetRelationshipsByType(stylesRelationshipType).FirstOrDefault();
                if (styleRelation != null)
                {
                    Uri styleUri =
                      PackUriHelper.ResolvePartUri(documentUri, styleRelation.TargetUri);
                    PackagePart stylePart = wdPackage.GetPart(styleUri);

                    //  Load the style XML in the part into an XDocument instance.
                    styleDoc = XDocument.Load(XmlReader.Create(stylePart.GetStream()));
                }
            }
        }

        string defaultStyle =
            (string)(
                from style in styleDoc.Root.Elements(w + "style")
                where (string)style.Attribute(w + "type") == "paragraph" &&
                      (string)style.Attribute(w + "default") == "1"
                select style
            ).First().Attribute(w + "styleId");

        // Find all paragraphs in the document.
        var paragraphs =
            from para in xDoc
                         .Root
                         .Element(w + "body")
                         .Descendants(w + "p")
            let styleNode = para
                            .Elements(w + "pPr")
                            .Elements(w + "pStyle")
                            .FirstOrDefault()
            select new
            {
                ParagraphNode = para,
                StyleName = styleNode != null ?
                    (string)styleNode.Attribute(w + "val") :
                    defaultStyle
            };

        // Retrieve the text of each paragraph.
        var paraWithText =
            from para in paragraphs
            select new
            {
                ParagraphNode = para.ParagraphNode,
                StyleName = para.StyleName,
                Text = para
                       .ParagraphNode
                       .Elements(w + "r")
                       .Elements(w + "t")
                       .StringConcatenate(e => (string)e)
            };

        foreach (var p in paraWithText)
            Console.WriteLine("StyleName:{0} >{1}<", p.StyleName, p.Text);
    }
}

This example produces the following output:

StyleName:Heading1 >Parsing WordprocessingML with LINQ to XML<
StyleName:Normal ><
StyleName:Normal >The following example prints to the console.<
StyleName:Normal ><
StyleName:Code >using System;<
StyleName:Code ><
StyleName:Code >class Program {<
StyleName:Code >    public static void (string[] args) {<
StyleName:Code >        Console.WriteLine("Hello World");<
StyleName:Code >    }<
StyleName:Code >}<
StyleName:Normal ><
StyleName:Normal >This example produces the following output:<
StyleName:Normal ><
StyleName:Code >Hello World<

This refactoring is a variant of refactoring into a pure function. The next article in this tutorial shows in more detail how to refactor this code into pure functions:

• Refactor using a pure function

See also

• Tutorial: Manipulate content in a WordprocessingML document
• Refactor into pure functions