1、使用StringBuilder替換

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication2
{
  class Program
  {
    static void Main(string[] args)
    {
      string str = "hello world! cjavapy!!!";
      StringBuilder sb = new StringBuilder(str);
      str = sb.Replace("!", "b", 0, str.IndexOf("!") + 1).ToString(); ;//指定替換的范圍實現替換一次,并且指定范圍中要只有一個替換的字符串
      Console.WriteLine(str);//輸出：hello worldb cjavapy!!!
      Console.ReadKey();
    }
  }
}

2、使用正則表達式(Regex)替換

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication2
{
  class Program
  {
    static void Main(string[] args)
    {
      string str = "hello world! cjavapy!!!";
      Regex regex = new Regex("!");//要替換字符串"!"
      str = regex.Replace(str, "b", 1);//最后一個參數是替換的次數
      Console.WriteLine(str);//輸出：hello worldb cjavapy!!!
      Console.ReadKey();
    }
  }
}

3、使用IndexOf和Substring替換

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication2
{
  class Program
  {
    static void Main(string[] args)
    {
      string str = "hello world! cjavapy!!!";
      StringBuilder sb = new StringBuilder(str);
      int index = str.IndexOf("!");
      str = str.Substring(0, index) + "b" + str.Substring(index + 1);//指定替換的范圍實現替換一次,并且指定范圍中要只有一個替換的字符串
      Console.WriteLine(str);//輸出：hello worldb cjavapy!!!
      Console.ReadKey();
    }
  }
}

4、通過擴展方法實現ReplaceOne

擴展方法實現代碼：

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication2
{
  public static class StringReplace
  {
  public static string ReplaceOne(this string str, string oldStr, string newStr)
    {
        StringBuilder sb = new StringBuilder(str);
      int index = str.IndexOf(oldStr);
      if (index > -1)
        return str.Substring(0, index) + newStr + str.Substring(index + oldStr.Length);
      return str;
    }
   }
}

調用代碼：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace ConsoleApplication2
{
  class Program
  {
    static void Main(string[] args)
    {
      string str = "hello world! cjavapy!!!";
      str = str.ReplaceOne("!","b");//通過擴展方法替換
      Console.WriteLine(str);//輸出：hello worldb cjavapy!!!
      Console.ReadKey();
    }
  }
}