问如何提取由空格分隔的字符串的一部分？

EN

string str ="hhB2LWq50a+9HZiNLKuwdQ==.pdf aaaaaaaa bbbbbbbbb cccccdddddeee";
int spacePos = str.IndexOf(' ');
if (spacePos == -1)
    return null;
else
    return str.Substring(0, spacePos);

string str ="hhB2LWq50a+9HZiNLKuwdQ==.pdf aaaaaaaa bbbbbbbbb cccccdddddeee";
string[] parts = str.Split(' ');
if (parts != null)
{
   string firstPart = parts[0];
}

using System.Linq;

string firstPart = str.Split(' ').First();

string tem = "test test";
string[] s = tem.Split(' ');
Console.WriteLine(s[0]);
Console.ReadLine();