String s = "one.two";
//Removes everything after first '.'
String result = s.substring(0, s.indexOf('.'));
print(result);
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to keep it even simpeler, with 's' as the initial string one.two then
s.substring(0, s.indexOf('.')) produces: one
and s.substring(s.indexOf('.') + 1) produces: two
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In case there are more than one '.' in the String it will use the first occurrance.
If you need to use the last one (to get rid of a file extension, for example) change
indexOf to lastIndexOf. If you are unsure there is at least one occurrance, you
should also add some validation to avoid triggering an exception.
String s = "one.two.three";
//Remove everything after last '.'
var pos = s.lastIndexOf('.');
String result = (pos != -1)? s.substring(0, pos): s;
print(result);