How to get ByteData from a File

问题

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?

回答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.

回答2:

Try this:

File file = getSomeCorrectFile(); 
ByteData bytes = await file.readAsBytes().then((data) => ByteData.view(data as ByteBuffer)); 
return bytes;

回答3:

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;

来源：https://stackoverflow.com/questions/56044473/how-to-get-bytedata-from-a-file

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dart

Flutter