network_to_file_image 2.2.4

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pub package

network_to_file_image #

This is a mixture of FileImage and NetworkImage. It will download the image from the url once, save it locally in the file system, and then use it from there in the future.

In more detail:

Given a file and url of an image, it first tries to read it from the local file. It decodes the given File object as an image, associating it with the given scale.

However, if the image doesn't yet exist as a local file, it fetches the given URL from the network, associating it with the given scale, and then saves it to the local file. The image will be cached regardless of cache headers from the server.

Notes:

  • If the provided url is null or empty, NetworkToFileImage will default to FileImage. It will read the image from the local file, and won't try to download it from the network.

  • If the provided file is null, NetworkToFileImage will default to NetworkImage. It will download the image from the network, and won't save it locally.

Use the package #

If you also listed path_provider in your pubspec.yaml file:

path_provider: ^1.4.4

Then you can create a file from a file name:

Future<File> file(String filename) async {
  Directory dir = await getApplicationDocumentsDirectory();
  String pathName = p.join(dir.path, filename);
  return File(pathName);
}

var myFile = await file("myFileName.png"),

Then, create the image:

Image(image: NetworkToFileImage(url: "http://example.com/someFile.png", file: myFile))

If you make debug: true it prints to the console whether the image was read from the file or fetched from the network:

Image(image: NetworkToFileImage(url: "http://example.com/someFile.png", file: myFile, debug: true))    

Don't forget to check the example tab.

Canvas #

You can also load images to use with the Canvas object of the paint method of a CustomPainter.

ImageProviders can't be used directly with the Canvas object, but you can use the provided ImageForCanvas class.

For example: Suppose a User object that contains url and filename properties:

 var imageForCanvas = ImageForCanvas<User>(
        imageProviderSupplier: (User user) => NetworkToFileImage(file: user.file, url: user.url),
        keySupplier: (User user) => user.filename,
        loadCallback: (image, obj, key) => setState((){}),
      );

 // While the image is downloading, this will return null.
 var myImage = imageForCanvas.image(user);

 if (myImage != null) {
    canvas.drawImage(myImage, ...);
    }

It will use the regular image cache from Flutter, and works not only with NetworkToFileImage provider, but any other image providers.

Tests #

You can set mock files (local and in the network). Please see methods:

  • setMockFile(File file, Uint8List bytes)
  • setMockUrl(String url, Uint8List bytes)
  • clearMocks()
  • clearMockFiles()
  • clearMockUrls()

Your mocked urls are usually only seen by the NetworkToFileImage class. However, you may override the default Dart http methods so that these urls are visible to other ImageProviders.

To that end, simply call this method:

NetworkToFileImage.startHttpOverride();

You can stop the http override by calling:

NetworkToFileImage.stopHttpOverride();

See also #


Special Thanks: Hugo Passos helped me with the http override.

The Flutter packages I've authored:

---
Marcelo Glasberg:
https://github.com/marcglasberg
https://twitter.com/glasbergmarcelo
https://stackoverflow.com/users/3411681/marcg
https://medium.com/@marcglasberg

[2.2.4] - 2019/12/21

  • Http override (mock urls visible to the whole app).

[2.2.1] - 2019/12/11

[2.1.5] - 2019/10/31

  • ImageForCanvas.

[2.0.7] - 2019/09/12

  • ErrorDescription.

[2.0.6] - 2019/08/13

  • Docs improvement.

[2.0.2] - 2019/06/24

  • Commented out the informationCollector, until version 1.7.8.

[2.0.0] - 2019/06/24

  • Reverted back to stable Flutter version 1.5.X.

[1.7.8] - 2019/06/24

  • Fixed for versions 1.7.8 and up.

[1.0.4] - 2019/02/22

  • This version works for the stable Flutter version 1.5.X.

[1.0.3] - 2019/01/16

  • Allow mock urls.

[1.0.2] - 2019/01/04

  • Details.

[1.0.1] - 2019/01/04

  • Allow mock files.

[1.0.0] - 2018/12/11

  • Tested thoroughly.

[0.0.2] - 2018/12/10

  • Corrected changelog and license.

[0.0.1] - 2018/12/10

  • Reads from the file, or fetches from the network and saves to the file.

example/lib/main.dart

import 'dart:async';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:network_to_file_image/network_to_file_image.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';

String flutterLogoUrl =
    "https://upload.wikimedia.org/wikipedia/commons/1/17/Google-flutter-logo.png";

String flutterLogoFileName = "flutter.png";

void main() async {
  runApp(
    MaterialApp(
      home: Demo(
        url: flutterLogoUrl,
        file: await file(flutterLogoFileName),
      ),
    ),
  );
}

Future<File> file(String filename) async {
  WidgetsFlutterBinding.ensureInitialized();
  Directory dir = await getApplicationDocumentsDirectory();
  String pathName = p.join(dir.path, filename);
  return File(pathName);
}

class Demo extends StatelessWidget {
  final String url;
  final File file;

  const Demo({Key key, this.url, this.file}) : super(key: key);

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(title: const Text('Network to file image example')),
        body: Padding(
          padding: const EdgeInsets.all(30.0),
          child: Image(image: NetworkToFileImage(url: url, file: file, debug: true)),
        ),
      );
}

Use this package as a library

1. Depend on it

Add this to your package's pubspec.yaml file:


dependencies:
  network_to_file_image: ^2.2.4

2. Install it

You can install packages from the command line:

with Flutter:


$ flutter pub get

Alternatively, your editor might support flutter pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:


import 'package:network_to_file_image/network_to_file_image.dart';
  
Popularity:
Describes how popular the package is relative to other packages. [more]
91
Health:
Code health derived from static analysis. [more]
100
Maintenance:
Reflects how tidy and up-to-date the package is. [more]
100
Overall:
Weighted score of the above. [more]
95
Learn more about scoring.

We analyzed this package on Jan 27, 2020, and provided a score, details, and suggestions below. Analysis was completed with status completed using:

  • Dart: 2.7.1
  • pana: 0.13.4
  • Flutter: 1.12.13+hotfix.5

Health suggestions

Fix lib/image_for_canvas.dart. (-0.50 points)

Analysis of lib/image_for_canvas.dart reported 1 hint:

line 68 col 44: The member 'load' can only be used within instance members of subclasses of 'package:flutter/src/painting/image_provider.dart'.

Format lib/network_to_file_image.dart.

Run flutter format to format lib/network_to_file_image.dart.

Dependencies

Package Constraint Resolved Available
Direct dependencies
Dart SDK >=2.7.0 <3.0.0
flutter 0.0.0
Transitive dependencies
collection 1.14.11 1.14.12
meta 1.1.8
sky_engine 0.0.99
typed_data 1.1.6
vector_math 2.0.8
Dev dependencies
flutter_test
path_provider ^1.4.4