你能控制 TagBuilder 类呈现属性的顺序吗？

Question

I know this is kind of obsessive, but is there a way to control the order that the TagBuilder class renders the attributes of an HTML tag when you call ToString() ?

ie so that

var tb = new TagBuilder("meta");            
tb.Attributes.Add("http-equiv", "Content-Type");            
tb.Attributes.Add("content", "text/html; charset=utf-8");    
tb.ToString(TagRenderMode.SelfClosing)

will return

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

not

<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />

Changing the order that you add the attributes doesn't change it, it seems to be rendering in alphabetical order

Answer 1

Try using this class, which inherits the TagBuilder and overrides the ToString method, building a SortedDictionary from the Attributes and using that dictionary to render.

    public class MyTagBuilder : TagBuilder
    {
        //required to inherit from TagBuilder
        public MyTagBuilder(string tagName) : base(tagName){}

        //new hides the original ToString(TagRenderMode renderMode) 
        //The only changes in this method is that all calls to GetAttributesString
        //have been changed to GetMyAttributesString 
        public new string ToString(TagRenderMode renderMode)
        {
            switch (renderMode)
            {
                case TagRenderMode.StartTag:
                    return string.Format(CultureInfo.InvariantCulture, "<{0}{1}>", new object[] { this.TagName, this.GetMyAttributesString() });

                case TagRenderMode.EndTag:
                    return string.Format(CultureInfo.InvariantCulture, "</{0}>", new object[] { this.TagName });

                case TagRenderMode.SelfClosing:
                    return string.Format(CultureInfo.InvariantCulture, "<{0}{1} />", new object[] { this.TagName, this.GetMyAttributesString() });
            }
            return string.Format(CultureInfo.InvariantCulture, "<{0}{1}>{2}</{0}>", new object[] { this.TagName, this.GetMyAttributesString(), this.InnerHtml });
        }

        //Implement GetMyAttributesString where the Attributes are changed to a SortedDictionary
        private string GetMyAttributesString()
        {
            var builder = new StringBuilder();
            var myDictionary = new SortedDictionary<string, string>();     //new
            foreach (KeyValuePair<string, string> pair in this.Attributes) //new
            {                                                              //new
                myDictionary.Add(pair.Key, pair.Value);                    //new
            }                                                              //new 
            //foreach (KeyValuePair<string, string> pair in this.Attributes)
            foreach (KeyValuePair<string, string> pair in myDictionary)    //changed
            {
                string key = pair.Key;
                if (!string.Equals(key, "id", StringComparison.Ordinal) || !string.IsNullOrEmpty(pair.Value))
                {
                    string str2 = HttpUtility.HtmlAttributeEncode(pair.Value);
                    builder.AppendFormat(CultureInfo.InvariantCulture, " {0}=\"{1}\"", new object[] { key, str2 });
                }
            }
            return builder.ToString();
        }
    }

Answer 2

I disassembled TagBuilder.ToString() with Reflector, and this is the key bit of code:

foreach (KeyValuePair<string, string> pair in this.Attributes)
{
    string key = pair.Key;
    string str2 = HttpUtility.HtmlAttributeEncode(pair.Value);
    builder.AppendFormat(CultureInfo.InvariantCulture, " {0}=\"{1}\"", new object[] { key, str2 });
}

So I would say not - this.Attributes is an IDictionary<string,string> interface, when enumerating over that "the order in which the items are returned is undefined," according to MSDN.

Answer 3

I did not want to override all that code to modify the sort behaviour so I changed the Attributes-property to a regular unsorted Dictionary with reflection instead

private class MyTagBuilder: TagBuilder
{
    private static readonly MethodInfo tagBuilderAttrSetMethod = typeof(TagBuilder).GetProperty(nameof(Attributes)).SetMethod;

    public MyTagBuilder(string tagName) : base(tagName)
    {
        // TagBuilder internally uses SortedDictionary, render attributes according to the order they are added instead
        tagBuilderAttrSetMethod.Invoke(this, new object[] { new Dictionary<string, string>() });
    }
}