在C＃中如何在字符串列表中传递string.empty

Question

i have a list of string

Emails = new List<string>() { "R.Dun@domain.co.nz", "S.Dun@domain.co.nz" }

now i want to pass string.empty to first value of list

something like

policy.Emails = new List<string>(){string.Empty};

how to put a loop for eg for each value of list do something.

Answer 1

您可以将第一个元素直接设置为string.Empty：

policy.Emails[0]=string.Empty;

Answer 2

You can use indexof function for finding a string in the list as below,

List<string> strList = new List<string>() { "R.Dun@domain.co.nz", "S.Dun@domain.co.nz" };

int fIndex = strList.IndexOf("R.Dun@domain.co.nz");

if(fIndex != -1)
    strList[fIndex] = string.Empty;

Or if you want to replace first item with string.Empty then as dasblinkenlight mentioned you can do using the index directly,

strList[0] = string.Empty

Hope it helps.

Answer 3

You can prepend string.Empty to an existing list with concat:

var emails = new List<string> {"R.Dun@domain.co.nz", "S.Dun@domain.co.nz"};
policy.Emails = new[] {string.Empty}.Concat(emails).ToList();

Now policy.Emails looks like this:

{"", "R.Dun@domain.co.nz", "S.Dun@domain.co.nz"}

If you would like to replace the first item, use Skip(1) before concatenating:

policy.Emails = new[] {string.Empty}.Concat(emails.Skip(1)).ToList();

To generalize, replacing the initial n values with empty strings would look like this:

policy.Emails = Enumerable.Repeat(string.Empty, 1).Concat(emails.Skip(n)).ToList();

Note: It goes without saying that if you do not mind modifying the list in place, the simplest solution is to do

emails[0] = string.Empty;

Answer 4

如果要在列表的开头添加空字符串，可以执行以下操作：

emails.Insert(0, string.Empty);