How to get ByteData from a File

Question

I want to convert a File to a ByteData object in flutter. Something like this:

import 'dart:io';
File file = getSomeCorrectFile(); //This file is correct
ByteData bytes = ByteData(file.readAsBytesSync()); //Doesnt compile
return bytes; 

I understood that ByteData constructor receives the length of the amount of bytes and initialize them with 0, so I could do something like ByteData(file.readAsBytesStync().length); but then how do I fill them? What am I missing?

Answer 1

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.