How to get ByteData from a File

In Dart 2.5.0 or later, I believe that the following should work:

import 'dart:io';
import 'dart:typed_data';

...
File file = getSomeCorrectFile();
Uint8List bytes = file.readAsBytesSync();
return ByteData.view(bytes.buffer);

(Prior to Dart 2.5.0, the file.readAsBytesSync() line should be:

Uint8List bytes = file.readAsBytesSync() as Uint8List;

File.readAsBytes/File.readAsBytesSync used to be declared to return a List<int>, but the returned object was actually a Uint8List subtype.)

Once you have the bytes as a Uint8List, you can extract its ByteBuffer and construct a ByteData from that.

in Dart 2.9:

import 'dart:io';
import 'dart:typed_data';

final file = getSomeCorrectFile(); // File
final bytes = await file.readAsBytes(); // Uint8List
final byteData = bytes.buffer.asByteData(); // ByteData

return byteData;

this is worked for me ...

  Uint8List uint8list = Uint8List.fromList(File(path).readAsBytesSync())