How to read bytes of a local image file in Dart/Fl

问题:

I would like to use a placeholder image file that I've added to my code as "assets/placeholder.png", but I'm getting a File not found error. This is how I'm doing it from the dartlang documentation...

var bytes = await new File('assets/placeholder.png').readAsBytes();
String base64 = CryptoUtils.bytesToBase64(bytes);

The bytes variable errors every time. How can I save the bytes of a locally saved image file?

回答1:

With Flutter environment, you have to use AssetBundle if you want to access to your assets (https://flutter.io/assets-and-images/).

import 'package:flutter/services.dart' show rootBundle;


ByteData bytes = await rootBundle.load('assets/placeholder.png');

回答2:

In dart Uint8List is equal to byte[].

1. Create one function and pass file path, It will return Bytes.

   Future<Uint8List> _readFileByte(String filePath) async {
       Uri myUri = Uri.parse(filePath);
       File audioFile = new File.fromUri(myUri);
       Uint8List bytes;
       await audioFile.readAsBytes().then((value) {
       bytes = Uint8List.fromList(value); 
       print('reading of bytes is completed');
     }).catchError((onError) {
         print('Exception Error while reading audio from path:' +
         onError.toString());
     });
     return bytes;
   }
   

2. Now call the function in to get bytes of file.

   try{
     Uint8List audioByte;
     String myPath= 'MyPath/abc.png';
     _readFileByte(myPath).then((bytesData) {
       audioByte = bytesData;
     //do your task here 
     });
   } catch (e) {
      // if path invalid or not able to read
     print(e);
   }
   

3. If you want base64String then use below code:

   String audioString = base64.encode(audioByte);

for base64 import 'dart:convert';

I hope it will help!