c# - StringBuilder - 查找字符的最后一个索引

Question

我想在 StringBuilder 中找到特定的最后一个字符。
我知道，我可以使用 while() 来解决它，但是是否有一个 build it 选项可以轻松做到这一点？

例如:

private static StringBuilder mySb = new StringBuilder("");
mySb.Add("This is a test[n] I like Orange juice[n] Can you give me some?");

现在:它应该找到 ] 并给我位置。喜欢:40

提前致谢

Answer 1

由于没有内置方法并且总是通过 ToString 从 StringBuilder 创建一个 string 可能效率很低，您可以创建一个扩展方法为此目的:

public static int LastIndexOf(this StringBuilder sb, char find, bool ignoreCase = false, int startIndex = -1, CultureInfo culture = null)
{
    if (sb == null) throw new ArgumentNullException(nameof(sb));
    if (startIndex == -1) startIndex = sb.Length - 1;
    if (startIndex < 0 || startIndex >= sb.Length) throw new ArgumentException("startIndex must be between 0 and sb.Lengh-1", nameof(sb));
    if (culture == null) culture = CultureInfo.InvariantCulture;

    int lastIndex = -1;
    if (ignoreCase) find = Char.ToUpper(find, culture);
    for (int i = startIndex; i >= 0; i--)
    {
        char c = ignoreCase ? Char.ToUpper(sb[i], culture) : (sb[i]);
        if (find == c)
        {
            lastIndex = i;
            break;
        }
    }
    return lastIndex;
}

将它添加到一个静态的、可访问的(扩展)类中，然后你就可以这样使用它了:

StringBuilder mySb = new StringBuilder("");
mySb.Append("This is a test[n] I like Orange juice[n] Can you give me some?");
int lastIndex = mySb.LastIndexOf(']');  // 39