C# implements case-insensitive retrieval and highlighting sample code sharing

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C# retrieval insensitive Detailed explanation of case and highlight display examples

Today, I encountered a problem: How to highlight case-insensitive keywords in a web page

For example: text abcaBcabCaBCabcaBCa, keyword bc, in case of insensitivity, there are 6 matches in total.

　What is displayed on the web page is abcaBcabCaBCabcaBCa.

Many people think of the replace function. But in c# the replace function cannot solve the letter case problem.

For example, bc, Bc, bC, and BC have all been searched, but they cannot be replaced by a single text.

The above text is reproduced from the article of Daniel "Wancang Yimi" - -"Highlight case-insensitive keywords - ASP".

But his article was written in the ASP version, and today I am writing the C# version; let’s talk about the solution below.

Solution: Use IndexOf

##                                                   ''''''''''''''''''''''''‑‑‑‑‑‑‐‐‐‐‐‐‐‐‐‐‐‐‐ The index of the first occurrence in the object. Parameters

value
类型： System. String 
要搜寻的字符串。
startIndex
类型： System. Int32 
搜索起始位置。
comparisonType
类型： System. StringComparison 
指定搜索规则的枚举值之一。
（OrdinalIgnoreCase：使用序号排序规则并忽略被比较字符串的大小写，对字符串进行比较。）

Code

/// <summary>
    /// 高亮查找关键字。
    /// </summary>
    /// <param name="str">文本。</param>
    /// <param name="keyword">关键字</param>
    /// <returns>含高亮标识的文本。</returns>
    /// <remarks>
    ///  1、字母不区分大小写。 
    ///  2、CssClass 名称为 highlight。
    /// </remarks>
    private string HighLightKeyword(string str, string keyword)
    {
      int index;
      var startIndex = 0;
      const string highLightBegin = "<span class=&#39;highlight&#39;>";
      const string highLightEnd = "</span>";
      var length = highLightBegin.Length + keyword.Length;
      var lengthHighlight = length + highLightEnd.Length;

      while ((index = str.IndexOf(keyword, startIndex, StringComparison.OrdinalIgnoreCase)) > -1)
      {
        str = str.Insert(index, highLightBegin).Insert(index + length, highLightEnd);
        startIndex = index + lengthHighlight;
      }

      return str;
    }

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