从MSDN:

如果指定的路径之一是长度为零的字符串，则此方法返回另一个路径。如果path2包含一个绝对路径，该方法返回path2。

在你的例子中，path2是绝对的。

遵循Christian Graus在他的博客“我讨厌微软的事情”中的建议。合并本质上是无用的。”下面是我的解决方案:

public static class Pathy
{
    public static string Combine(string path1, string path2)
    {
        if (path1 == null) return path2
        else if (path2 == null) return path1
        else return path1.Trim().TrimEnd(System.IO.Path.DirectorySeparatorChar)
           + System.IO.Path.DirectorySeparatorChar
           + path2.Trim().TrimStart(System.IO.Path.DirectorySeparatorChar);
    }

    public static string Combine(string path1, string path2, string path3)
    {
        return Combine(Combine(path1, path2), path3);
    }
}

一些人建议名称空间应该冲突，…为了避免与System.IO.Path的名称空间冲突，我选择了Pathy。

编辑:增加空参数检查

这是. net Reflector for Path的反汇编代码。结合的方法。检查ispathoot函数。如果第二个路径是根路径(以DirectorySeparatorChar开头)，则返回第二个路径。

public static string Combine(string path1, string path2)
{
    if ((path1 == null) || (path2 == null))
    {
        throw new ArgumentNullException((path1 == null) ? "path1" : "path2");
    }
    CheckInvalidPathChars(path1);
    CheckInvalidPathChars(path2);
    if (path2.Length == 0)
    {
        return path1;
    }
    if (path1.Length == 0)
    {
        return path2;
    }
    if (IsPathRooted(path2))
    {
        return path2;
    }
    char ch = path1[path1.Length - 1];
    if (((ch != DirectorySeparatorChar) &&
         (ch != AltDirectorySeparatorChar)) &&
         (ch != VolumeSeparatorChar))
    {
        return (path1 + DirectorySeparatorChar + path2);
    }
    return (path1 + path2);
}


public static bool IsPathRooted(string path)
{
    if (path != null)
    {
        CheckInvalidPathChars(path);
        int length = path.Length;
        if (
              (
                  (length >= 1) &&
                  (
                      (path[0] == DirectorySeparatorChar) ||
                      (path[0] == AltDirectorySeparatorChar)
                  )
              )

              ||

              ((length >= 2) &&
              (path[1] == VolumeSeparatorChar))
           )
        {
            return true;
        }
    }
    return false;
}

In my opinion this is a bug. The problem is that there are two different types of "absolute" paths. The path "d:\mydir\myfile.txt" is absolute, the path "\mydir\myfile.txt" is also considered to be "absolute" even though it is missing the drive letter. The correct behavior, in my opinion, would be to prepend the drive letter from the first path when the second path starts with the directory separator (and is not a UNC path). I would recommend writing your own helper wrapper function which has the behavior you desire if you need it.

这段代码应该做到这一点:

        string strFinalPath = string.Empty;
        string normalizedFirstPath = Path1.TrimEnd(new char[] { '\\' });
        string normalizedSecondPath = Path2.TrimStart(new char[] { '\\' });
        strFinalPath =  Path.Combine(normalizedFirstPath, normalizedSecondPath);
        return strFinalPath;

由于不知道实际的细节，我猜测它尝试像连接相对uri那样连接。例如:

urljoin('/some/abs/path', '../other') = '/some/abs/other'

这意味着当您使用前面的斜杠连接路径时，实际上是将一个基底连接到另一个基底，在这种情况下，第二个基底优先。