parse method Null safety

Parse source as a, possibly signed, integer literal and return its value.

The source must be a non-empty sequence of base-radix digits, optionally prefixed with a minus or plus sign ('-' or '+'). It must not be null.

The radix must be in the range 2..36. The digits used are first the decimal digits 0..9, and then the letters 'a'..'z' with values 10 through 35. Also accepts upper-case letters with the same values as the lower-case ones.

If no radix is given then it defaults to 10. In this case, the source digits may also start with 0x, in which case the number is interpreted as a hexadecimal integer literal, When int is implemented by 64-bit signed integers, hexadecimal integer literals may represent values larger than 2⁶³, in which case the value is parsed as if it is an unsigned number, and the resulting value is the corresponding signed integer value.

For any int n and valid radix r, it is guaranteed that n == int.parse(n.toRadixString(r), radix: r).

If the source string does not contain a valid integer literal, optionally prefixed by a sign, a FormatException is thrown (unless the deprecated onError parameter is used, see below).

Instead of throwing and immediately catching the FormatException, instead use tryParse to handle a parsing error. Example:

var value = int.tryParse(text);
if (value == null) ... handle the problem

The onError parameter is deprecated and will be removed. Instead of int.parse(string, onError: (string) => ...), you should use int.tryParse(string) ?? (...).

When the source string is not valid and onError is provided, whenever a FormatException would be thrown, onError is instead called with source as argument, and the result of that call is returned by parse.