UTF-16 safe substring in C# .NET

Question

I want to get a substring of a given length say 150. However, I want to make sure I don't cut off the string in between a unicode character.

e.g. see the following code:

var str = "Hello😀 world!";
var substr = str.Substring(0, 6);

Here substr is an invalid string since the smiley character is cut in half.

Instead I want a function that does as follows:

var str = "Hello😀 world!";
var substr = str.UnicodeSafeSubstring(0, 6);

where substr contains "Hello😀"

For reference, here is how I would do it in Objective-C using rangeOfComposedCharacterSequencesForRange

NSString* str = @"Hello😀 world!";
NSRange range = [message rangeOfComposedCharacterSequencesForRange:NSMakeRange(0, 6)];
NSString* substr = [message substringWithRange:range]];

What is the equivalent code in C#?

Answer 1

Looks like you're looking to split a string on graphemes, that is on single displayed characters.

In that case, you have a handy method: StringInfo.SubstringByTextElements:

var str = "Hello😀 world!";
var substr = new StringInfo(str).SubstringByTextElements(0, 6);