{"id":535,"date":"2003-11-06T20:58:13","date_gmt":"2003-11-07T00:58:13","guid":{"rendered":"http:\/\/wordpress.cephas.net\/?p=535"},"modified":"2003-11-06T20:58:13","modified_gmt":"2003-11-07T00:58:13","slug":"c-indexers","status":"publish","type":"post","link":"https:\/\/cephas.net\/blog\/2003\/11\/06\/c-indexers\/","title":{"rendered":"C# Indexers"},"content":{"rendered":"

At Mindseye<\/a> we’ve written a content management system, which is really just the net result of writing and improving upon a modular code base for a bunch of different websites in a variety of programming languages (ASP.NET, ASP, ColdFusion, and Java). In this content management system, which we’ve affectionately called ‘Element’<\/a>, a website is distilled down in various ‘objects’; things like events, newsletters, products, etc. Long story short, each object (in whatever language) is usually represented as a specific type and is represented internally as an XML document. In the .NET\/C# version that I’ve been working with lately, a newsletter would look vaguely like this:
\n
\npublic class Newsletter {
\n  private XmlDocument<\/a> newsletter;
\n  public Newsletter(XmlDocument doc) {
\n   this.newsletter = doc;
\n  }
\n  \/\/ other methods left out
\n}
\n<\/code>
\nPutting aside your opinion on this being a good or bad design for a second, I’ve always struggled with how to best make the elements of the encapsulated xml document available to external classes. Right now I have a method:
\n
\npublic string GetProperty(string label) {
\n  \/\/ retrieve the appropriate element and return as string
\n  return theValue;
\n}
\n<\/code>
\nand this works pretty well, but it’s lengthy. Another way of doing it would be to make each element of the XmlDocument a public property<\/a>, but this would require alot of typing and would require that you recompile the class everytime the data structure it represented changed. So tonight, during nerd time (ie: extended time by myself at Barnes and Noble) I read about C# indexers. You’ve probably used an indexer before; for instance the NameValueCollection<\/a> class contains a public property called Item<\/a>, which itself is a indexer for a specific entry in the NameValueCollection. Unbeknownst to me before tonight, you can create your own indexers, so instead of having to access an element of an object like this:
\n
\nstring newsletterLabel = newsletterInstance.GetProperty(\"label\");
\n<\/code>
\nyou could instead use this syntax:
\n
\nstring newsletterLabel = newsletterInstance[\"label\"];
\n<\/code>
\nwhich just feels more natural to me. Implementing the indexer in your class is simple. Using the example ‘Newsletter’ class above:
\n
\npublic class Newsletter {
\n  private XmlDocument newsletter;
\n  public Newsletter(XmlDocument doc) {
\n   this.newsletter = doc;
\n  }
\n  \/\/ indexer
\n  public string this [string index] {
\n    get {
\n      \/\/ logic to retrieve appropriate element from xmldoc by name
\n      return theValue;
\n    }
\n  }
\n}
\n<\/code>
\nI’m guessing that generally the index will be an integer rather than the string that I have above, nothing much changes if the parameter is integer:
\n
\npublic string this [int index] {
\n  get {
\n    \/\/ logic to retrieve appropriate element from xmldoc by index
\n    return theValue;
\n  }
\n}
\n<\/code>
\nExtremely handy stuff to know! Couple more thoughts on the subject:<\/p>\n

· Indexers<\/a>
\n· Comparison Between Properties and Indexers<\/a>
\n· Properties<\/a>
\n· Developer.com: Using Indexers<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

At Mindseye we’ve written a content management system, which is really just the net result of writing and improving upon a modular code base for a bunch of different websites in a variety of programming languages (ASP.NET, ASP, ColdFusion, and Java). In this content management system, which we’ve affectionately called ‘Element’, a website is distilled … Continue reading C# Indexers<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[17],"tags":[],"_links":{"self":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts\/535"}],"collection":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/comments?post=535"}],"version-history":[{"count":0,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/posts\/535\/revisions"}],"wp:attachment":[{"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/media?parent=535"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/categories?post=535"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cephas.net\/blog\/wp-json\/wp\/v2\/tags?post=535"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}