你能控制 TagBuilder 类呈现属性的顺序吗？答案

【问题标题】：Can you control the order in which the TagBuilder class renders attributes?你能控制 TagBuilder 类呈现属性的顺序吗？
【发布时间】：2011-03-28 18:50:54
【问题描述】：

我知道这有点强迫症，但是当您调用ToString() 时，有没有办法控制TagBuilder 类呈现HTML 标记的属性的顺序？

即这样

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)

会回来

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

不是

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

更改添加属性的顺序并不会改变它，它似乎是按字母顺序呈现的

【问题讨论】：

标签： c# asp.net tagbuilder

【解决方案1】：

尝试使用这个类，它继承 TagBuilder 并覆盖 ToString 方法，从 Attributes 构建一个 SortedDictionary 并使用该字典进行渲染。

    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();
        }
    }

【讨论】：

【解决方案2】：

我用 Reflector 反汇编了TagBuilder.ToString()，这是代码的关键位：

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 });
}

所以我会说不是 - this.Attributes 是一个 IDictionary<string,string> 接口，当枚举“项目返回的顺序未定义”时，根据 MSDN。

【讨论】：

仅供参考，如果您查看标签构建器构造函数，IDictionary 实际上是一个 SortedDictionary

【解决方案3】：

我不想重写所有代码来修改排序行为，所以我将 Attributes-property 更改为带有反射的常规未排序字典

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>() });
    }
}

【讨论】：