Firebase_Cached_Image

Cache Manager and Cached ImageProvider for Firebase Cloud Storage Objects.

Set up

Setup firebase (https://firebase.google.com/docs/flutter/setup).

Note

No support for caching in web, everything will be downloaded from server.

Firebase Image Provider

If you want to show image from your cloud storage then pass FirebaseImageProvider as ImageProvider to Image Widget. In FirebaseImageProvider pass FirebaseUrl.

Image(
  image: FirebaseImageProvider(
    FirebaseUrl("gs://bucket_f233/logo.jpg")
  ),
),

You can declare FirebaseUrl in following ways:

FirebaseUrl("gs://bucket_f233/logo.jpg")
FirebaseUrl("https://firebasestorage.googleapis.com/b/bucket/o/logo.jpg")
FirebaseUrl.fromReference(FirebaseStorage.instance.ref("images/image.jpg"));

You can alter default caching behaviour by passing CacheOptions to provider.

Image(
  image: FirebaseImageProvider(
    FirebaseUrl("gs://bucket_f233/logo.jpg"),
    options: CacheOptions(
      // Source from image will be fetched
      //
      // Default [Source.cacheServer]
      source: Source.server,
    ),
    errorBuilder: (context, error, stackTrace) {
      // [ImageNotFoundException] will be thrown if image does not exist on server.
      if (error is ImageNotFoundException) {
        return const Text('Image not found on Cloud Storage.');
      } else {
        return Text('Error loading image: $error');
      }
    },
    // The loading progress may not be accurate as Firebase Storage API
    // does not provide a stream of bytes downloaded. The progress updates only at the start and end of the loading process.
    loadingBuilder: (_, Widget child, ImageChunkEvent? loadingProgress) {
      if (loadingProgress == null) {
        // Show the loaded image if loading is complete.
        return child;
      } else {
        return CircularProgressIndicator();
      }
    },
  ),
),

By default it will first try to fetch the image from cache, if image exists then it will be returned otherwise image will be fetched from server and then cached.

If you want to always fetch latest image from server then pass Source.server to CacheOptions.source.

  source: Source.server,

If you want to fetch image from server only if it is updated after last fetched then set checkIfFileUpdatedOnServer to false.

  checkIfFileUpdatedOnServer: true,

Image updation is checked by fetching image's metadata (modified timestamp) from server then comparing to cached image's metadata (modified timestamp).

Note: Metadata retrieval is a Class B operation in google cloud storage. you will be charged for that. Check pricing here (https://cloud.google.com/storage/pricing#price-tables) .Google does offer 50,000 free Class B operations per month.

---

Firebase Cache Manager

if you want to work with any type of cloud storage file and want more functionality then use FirebaseCacheManager.

Download and cache any file.

final file = await FirebaseCacheManager().getSingleFile(
  FirebaseUrl("gs://bucket_f233/doc.docx"),
);
print(file); // Cached file's path, can be used for sharing file

Download and cache file before use. Can be useful for caching frequently used image at app's load time.

await FirebaseCacheManager().preCache(
  FirebaseUrl("gs://bucket_f233/profile_pic.jpg"),
)

Refresh already cached file..

Checks if the file has been updated in server, then download the file if it has been updated and saves it to cache.

await FirebaseCacheManager().refreshCachedFile(
  FirebaseUrl("gs://bucket_f233/profile_pic.jpg"),
);

Copy file to cache

To manually copy file to cache, use this method. To avoid downloading the file again. It will copy the file from [filePath] to cache and return the cached file path.

final filePath = "/storage/file.jpg";
final cachedFilePath = await FirebaseCacheManager().copyToCache(
  FirebaseUrl("gs://bucket_f233/profile_pic.jpg"),
  filePath,
)

Delete specific file from cache.

await FirebaseCacheManager().delete(
  FirebaseUrl("gs://bucket_f233/logo.jpg"),
);

Clear all the cache.

await FirebaseCacheManager().clearCache();

// Delete files older than 20 days
await FirebaseCacheManager().clearCache(modifiedBefore: Duration(days: 20));

Use custom sub-directory to save files in desired directory in system's temporary directory. Default is "flutter_cached_image"

final manager = FirbaseCacheManager(subDir: "profile_pictures");

Also helpful in saving files in multiple folders

final profilePicturesCacheManager = FirbaseCacheManager(subDir: "profile_pictures");
final postsCacheManager = FirbaseCacheManager(subDir: "posts");

// Only delete files in posts directory
await postsCacheManger.clearCache();