string的常用操作

001-集合中的元素，用某个字符串连起来

还可以只把复杂类型的List中的某个字段/属性连接

有一个数据结构

public class Student
{
    public int ID { get; set; }

    public string Name { get; set; }
} 

List<int> list1 = new List<int> { 1, 2, 3, 4, 5, 7, 9 };
string result1 = string.Join(",", list1);
//结果：1,2,3,4,5,7,9

List<Student> list2 = new List<Student>();
for (int i = 0; i < 5; i++)
{
    list2.Add(new Student() { ID = i, Name = "SW" + i.ToString() });
}
string result2 = string.Join(",", list2.Select(t => t.Name));
//结果：SW0,SW1,SW2,SW3,SW4 

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002-去掉字符串两端空格以及去掉字符串中多余空格保留一个空格 

string str = "   abcd    efg        hij klmno pq ";
string[] strs = str.Trim().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
string finallStr = string.Join(" ", strs);
//结果："abcd efg hij klmno pq"