在 C# 中转换列表<dynamic>列出<string>

Question

Suppose I have a List<dynamic> object containing strings:

var dlist = new List<dynamic>()
{
    "test",
    "test2",
    "test3"
};

Is there any efficient way of converting this into a proper List<string> object? I know I can iterate over this list and cast each element to a string, then add this to the result list, but maybe some Linq magic could do the trick in one line?

I tried using some Select() combined with ToList() and Cast<string> , but to no avail. How should this be done properly?

Note : By saying "efficient" I mean of course number of lines of code. I do not take execution time or performance into account. Also - let's suppose I do not need to type check, there will always be strings only in this dynamic list.

EDIT: Okay, so in regards to comments on "why Cast wasn't working for you" - looks like I had another problem regarding the data I receive (I'm using Dapper) and that's why it didn't work. Sorry for the confusion, I thought my list converting was wrong while the problem was not related to this.

Answer 1

Given

var dList = new List<dynamic>() { /*...initialize list */ };

If you are interested in extracting all the strings in the collection, ignoring all other types, you can use:

// Solution 1: Include only strings, no null values, no exceptions thrown
var strings = dlist.OfType<string>().ToList();

If you are certain that all the items in the list are strings (it will throw an exception if they are not), you can use:

// Solution 2: Include strings with null values, Exception for other data types thrown
var strings = dlist.Cast<string>().ToList();

If you want the default string representation, with null for null values, of all the items in the list, you can use:

// Solution 3: Include all, regardless of data type, no exceptions thrown
var strings = dlist.Select(item => item?.ToString()).ToList();

Answer 2

This answer is for dart/flutter

Given

List<dynamic> dList;

You can use

var sList = List<String>.from(dlist);

to convert a List<dynamic> to List<String>