add onError which allows the user to supply their own response to firebase storage errors

Author: rsnider19

lib/src/firebase_image.dart

@@ -9,8 +9,11 @@ import 'package:firebase_storage/firebase_storage.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 
+import 'cache_manager.dart';
 import 'image_fetch_strategy.dart';
 
+typedef FirebaseImageError = Uint8List Function(Exception exception);
+
 class FirebaseImage extends ImageProvider<FirebaseImage> {
   // Default: True. Specified whether or not an image should be cached (optional)
   final bool shouldCache;
@@ -33,6 +36,11 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
   /// Default: FETCH_TO_MEMORY. Specifies the strategy in which to fetch the image from Firebase (optional)
   final ImageFetchStrategy imageFetchStrategy;
 
+  /// An optional response to when an error occurs (optional)
+  final FirebaseImageError onError;
+
+  final FirebaseImageCacheManager _cacheManager;
+
   /// Fetches, saves and returns an ImageProvider for any image in a readable Firebase Cloud Storeage bucket.
   ///
   /// [location] The URI of the image, in the bucket, to be displayed
@@ -49,11 +57,16 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
     this.cacheRefreshStrategy = CacheRefreshStrategy.BY_METADATA_DATE,
     this.firebaseApp,
     this.imageFetchStrategy = ImageFetchStrategy.FETCH_TO_MEMORY,
+    this.onError,
   }) : _imageObject = FirebaseImageObject(
           bucket: _getBucket(location),
           remotePath: _getImagePath(location),
           reference: _getImageRef(location, firebaseApp),
-        );
+        ),
+      _cacheManager = FirebaseImageCacheManager(
+        cacheRefreshStrategy: cacheRefreshStrategy,
+        imageFetchStrategy: imageFetchStrategy,
+      );
 
   /// Returns the image as bytes
   Future<Uint8List> getBytes() {
@@ -79,29 +92,34 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
 
   Future<Uint8List> _fetchImage() async {
     Uint8List bytes;
-    FirebaseImageCacheManager cacheManager = FirebaseImageCacheManager(
-      cacheRefreshStrategy: cacheRefreshStrategy,
-      imageFetchStrategy: imageFetchStrategy,
-    );
 
-    if (shouldCache) {
-      await cacheManager.open();
-      FirebaseImageObject localObject =
-          await cacheManager.get(_imageObject.uri, this);
+    try {
+      if (shouldCache) {
+        await _cacheManager.open();
+        FirebaseImageObject localObject =
+        await _cacheManager.get(_imageObject.uri, this);
 
-      if (localObject != null) {
-        bytes = await cacheManager.localFileBytes(localObject);
-        if (bytes == null) {
-          bytes = await cacheManager.upsertRemoteFileToCache(
+        if (localObject != null) {
+          bytes = await _cacheManager.localFileBytes(localObject);
+          if (bytes == null) {
+            bytes = await _cacheManager.upsertRemoteFileToCache(
               _imageObject, this.maxSizeBytes);
+          }
+        } else {
+          bytes = await _cacheManager.upsertRemoteFileToCache(
+            _imageObject, this.maxSizeBytes);
         }
       } else {
-        bytes = await cacheManager.upsertRemoteFileToCache(
-            _imageObject, this.maxSizeBytes);
+        bytes =
+        await _cacheManager.remoteFileBytes(_imageObject, this.maxSizeBytes);
+      }
+    }
+    catch (ex) {
+      await delete();
+
+      if (this.onError != null) {
+        bytes = this.onError(ex);
       }
-    } else {
-      bytes =
-          await cacheManager.remoteFileBytes(_imageObject, this.maxSizeBytes);
     }
 
     return bytes;
@@ -112,6 +130,13 @@ class FirebaseImage extends ImageProvider<FirebaseImage> {
         .instantiateImageCodec(await _fetchImage());
   }
 
+  Future<bool> delete() async {
+    await _cacheManager.open();
+    await _cacheManager.delete(_imageObject.uri);
+
+    return super.evict();
+  }
+
   @override
   Future<FirebaseImage> obtainKey(ImageConfiguration configuration) {
     return SynchronousFuture<FirebaseImage>(this);