Check if a file exists before loading it

Question

What I want to do is load an image in a Material Widget to use it in a ListTile, but this asset might not exist.

class MyImage extends StatelessWidget {
  final imagePath;

  MyIcon(String iconName) {
    try { // check if imagePath exists. Here is the problem
      imagePath = check('assets/$iconName.png/');
    } catch (e, s) { // if not
      imagePath = 'assets/$iconName.png/';
    }
  }

 @override
  Widget build(BuildContext context) {
    return Material(...here I will load the imagePath...);
 }
}

So, since I'm using a Stateless widget, I have to know beforehand if the image exists, otherwise I'll load a null right?

score 102 · Accepted Answer · edited Mar 13 '22 at 12:26

102

In order to see whether or not a file exists in internal local storage of the app use:

import 'dart:io' as io;
var syncPath = await path;

// for a file
await io.File(syncPath).exists();
io.File(syncPath).existsSync();

// for a directory
await io.Directory(syncPath).exists();
io.Directory(syncPath).existsSync();

edited Mar 13 '22 at 12:26

Sisir

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answered Mar 06 '19 at 14:17

Nae

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How to check if given path is filepath in device or network path from server? – Jay Mungara Sep 27 '19 at 10:41
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@JayMungara You can use **isURL('path')** method from [Validators](https://pub.dev/packages/validators) plugin to differentiate b/w Local and Network links. – CodeGeek Dec 11 '20 at 16:25
3

File(path).exists() returns a future bool. To implement this in a stateless widget, or to just check using if statement, use File(path).existsSync() which returns a bool data type. – jayesh saha Dec 29 '20 at 04:59
@JayMungara - did you find an answer? – Ayush Mandowara Dec 25 '21 at 12:56
@CodeGeek your solution is not applicable to this problem. – Ayush Mandowara Dec 25 '21 at 13:43
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@Nae Pls don't recommend the slow async API. Dart itself discourages this, see the Linter Rule "avoid_slow_async_io" -> https://dart-lang.github.io/linter/lints/avoid_slow_async_io.html – Georg Muehlenberg Oct 18 '22 at 11:57

score 40 · Answer 2 · answered Sep 26 '20 at 15:42

40

For me simply worked this:

import 'dart:io';
File("path/to/file").exists()

or, for checking it synchronously

import 'dart:io';
File("path/to/file").existsSync()

answered Sep 26 '20 at 15:42

Giuse Petroso

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`await File("path/to/file").exists()` is the same as `File("path/to/file").existsSync()` right? Why do they both exist? – Joran Dec 12 '20 at 12:56
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@Joran I think they exists because you may be in a closure which isn't marked with async keyword but you want to wait for the result. I think it's on purpose. – Giuse Petroso Jan 07 '21 at 17:43

Richard Heap · Answer 3 · 2018-10-03T22:05:26.907

17

Looks like you want to try to load an ImageProvider from a folder where the image may or may not exist and then, if it does not, load a fallback asset image (which you can be sure will exist as you'll put it in your root bundle).

Try this:

ImageProvider getImageProvider(File f) {
  return f.existsSync()
      ? FileImage(f)
      : const AssetImage('images/fallback.png');
}

edited Oct 03 '18 at 22:05

answered Oct 03 '18 at 21:58

Richard Heap

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Thanks! That's what I was looking for, but for some reason `f.existsSync()` always returns `false`. – Isaac Oct 04 '18 at 09:37
3

Ok, I think that this does not work. `f.existsSync` is always going to be false because assets are not files. They are bundles within the executable, according to a comment from this new question I asked https://stackoverflow.com/questions/52653032/flutter-file-existssync-always-returns-false – Isaac Oct 05 '18 at 12:39
As I said before, you don't need to test whether assets exist - you know that at build time. But in the comment you say "which I'll previously download (semi-automatically)", so these you will have written to a read/write folder and can test whether they exist. – Richard Heap Oct 05 '18 at 13:27
I don't understand. These files are written to the assets folder, the assets folder is mentioned in the pubspec, then the app is compiled. Then I need to test whenever the user want to see some info from this team, if its icon exists because it's not sure that every team has its icon. – Isaac Oct 05 '18 at 15:29
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So, what you really want to know is whether an asset exists. The best way to do this is to include an additional (text? json?) asset that is a list of all the other assets. In fact, flutter creates one for you. It's called `AssetManifest.json`. It's an implementation detail, so may change, but seems to work for now. – Richard Heap Oct 05 '18 at 15:37
Great! I'll take a look at that – Isaac Oct 05 '18 at 15:48

score -3 · Answer 4 · answered Oct 22 '21 at 17:01

-3

In order to see whether or not a file exists in local storage (as with image.network) now you can use :

Image.file(File("path/to/file"),
errorBuilder: (BuildContext context, Object exception, StackTrace? stackTrace) {return Text('file access error');

answered Oct 22 '21 at 17:01

MaB

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This does not answer the op's question. – Mahesh Jamdade Nov 09 '21 at 07:19

Check if a file exists before loading it

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