How to resolve an ImageProvider without BuildContext - flutter

Question

My question is pretty straightforward, I think, but I haven't been able to find an answer anywhere. I am passing an ImageProvider to my PixelData class to be able to access individual pixel color values, but I need to get the ui.Image and the image byte data out of the ImageProvider. I'm running into the issue shown below where I can't access those values without using createLocalImageConfiguration(buildContext) with the current BuildContext. I would like to be able to use this class outside of the BuildContext scope and so I need to be able to get the image data without the BuildContext.
I would really appreciate any help/guidance with this problem.
Thank you!
class PixelData {
ImageProvider imageProvider;
ui.Image _image;
ByteData _byteData;
int _width;
int _height;
PixelData(this.imageProvider) : assert(imageProvider != null);
int get width => _width;
int get height => _height;
Future<void> getByteData() async {
if (imageProvider == null) throw Exception("imageProvider is null");
// TODO here lies the problem.
// TODO how can I provide an ImageConfiguration without BuildContext?
// I can't use: createLocalImageConfiguration(buildContext)
imageProvider.resolve(configuration).addListener(
ImageStreamListener(
(info, _) async {
_image = info.image;
_width = _image.width;
_height = _image.height;
_byteData =
await _image.toByteData(format: ui.ImageByteFormat.rawRgba);
},
),
);
}
void getColorAt() {
// TODO
}
}
I tried using ImageConfiguration.empty, which is recommended when the context isn't available.
Here is the relevant updated code and the error that came after trying to run it.
/// getByteData must be called before trying to access pixel data
Future<void> getByteData() async {
if (imageProvider == null) throw Exception("imageProvider is null");
imageProvider.resolve(ImageConfiguration.empty).addListener(
ImageStreamListener(
(info, _) async {
print("code reached");
_image = info.image;
_width = _image.width;
_height = _image.height;
_byteData =
await _image.toByteData(format: ui.ImageByteFormat.rawRgba);
},
),
);
}
/// Pixel coordinates: (0,0) → (width-1, height-1).
Color pixelColorAt(int x, int y) {
if (_byteData == null ||
width == null ||
height == null ||
x < 0 ||
x >= width ||
y < 0 ||
y >= height)
return null;
else {
var byteOffset = 4 * (x + (y * width));
return _colorAtByteOffset(byteOffset);
}
}
test('test network image', () async {
String url =
"https://i0.wp.com/www.dignited.com/wp-content/uploads/2012/09/Magazine-QR-Code.jpg?fit=500%2C404&ssl=1";
final PixelData pixelData = PixelData(imageProvider: NetworkImage(url));
await pixelData.getByteData();
Color a = pixelData.pixelColorAt(282, 287);
Color b = pixelData.pixelColorAt(218, 105);
Color c = pixelData.pixelColorAt(160, 93);
Color d = pixelData.pixelColorAt(-1, 100);
print(a.value);
print(b.value);
print(c.value);
expect(d, null);
});
══╡ EXCEPTION CAUGHT BY IMAGE RESOURCE SERVICE ╞════════════════════════════════════════════════════
The following _CastError was thrown while resolving an image:
Null check operator used on a null value
When the exception was thrown, this was the stack:
#0 ImageProvider.resolveStreamForKey (package:flutter/src/painting/image_provider.dart:502:69)
#1 ImageProvider.resolve.<anonymous closure> (package:flutter/src/painting/image_provider.dart:333:9)
#2 ImageProvider._createErrorHandlerAndKey.<anonymous closure>.<anonymous closure> (package:flutter/src/painting/image_provider.dart:463:26)
#3 SynchronousFuture.then (package:flutter/src/foundation/synchronous_future.dart:41:35)
#4 ImageProvider._createErrorHandlerAndKey.<anonymous closure> (package:flutter/src/painting/image_provider.dart:460:11)
#8 ImageProvider._createErrorHandlerAndKey (package:flutter/src/painting/image_provider.dart:452:16)
#9 ImageProvider.resolve (package:flutter/src/painting/image_provider.dart:330:5)
#10 PixelData.getByteData (package:pixel_data/simplifying_image_pixels.dart:26:19)
#11 main.<anonymous closure> (file:///Users/graysonharrington/Documents/Programming/Flutter/apps/pixel_data/test/pixel_data_test.dart:14:21)
#12 Declarer.test.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart:175:19)
<asynchronous suspension>
#13 Declarer.test.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/declarer.dart)
#18 Declarer.test.<anonymous closure> (package:test_api/src/backend/declarer.dart:173:13)
#19 Invoker.waitForOutstandingCallbacks.<anonymous closure> (package:test_api/src/backend/invoker.dart:231:15)
#24 Invoker.waitForOutstandingCallbacks (package:test_api/src/backend/invoker.dart:228:5)
#25 Invoker._onRun.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart:383:17)
<asynchronous suspension>
#26 Invoker._onRun.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart)
#31 Invoker._onRun.<anonymous closure>.<anonymous closure> (package:test_api/src/backend/invoker.dart:370:9)
#32 Invoker._guardIfGuarded (package:test_api/src/backend/invoker.dart:415:15)
#33 Invoker._onRun.<anonymous closure> (package:test_api/src/backend/invoker.dart:369:7)
#40 Invoker._onRun (package:test_api/src/backend/invoker.dart:368:11)
#41 LiveTestController.run (package:test_api/src/backend/live_test_controller.dart:153:11)
#42 RemoteListener._runLiveTest.<anonymous closure> (package:test_api/src/remote_listener.dart:256:16)
#47 RemoteListener._runLiveTest (package:test_api/src/remote_listener.dart:255:5)
#48 RemoteListener._serializeTest.<anonymous closure> (package:test_api/src/remote_listener.dart:208:7)
#66 _GuaranteeSink.add (package:stream_channel/src/guarantee_channel.dart:125:12)
#67 new _MultiChannel.<anonymous closure> (package:stream_channel/src/multi_channel.dart:159:31)
#71 CastStreamSubscription._onData (dart:_internal/async_cast.dart:85:11)
#105 new _WebSocketImpl._fromSocket.<anonymous closure> (dart:_http/websocket_impl.dart:1145:21)
#113 _WebSocketProtocolTransformer._messageFrameEnd (dart:_http/websocket_impl.dart:338:23)
#114 _WebSocketProtocolTransformer.add (dart:_http/websocket_impl.dart:232:46)
#124 _Socket._onData (dart:io-patch/socket_patch.dart:2044:41)
#133 new _RawSocket.<anonymous closure> (dart:io-patch/socket_patch.dart:1580:33)
#134 _NativeSocket.issueReadEvent.issue (dart:io-patch/socket_patch.dart:1076:14)
(elided 104 frames from dart:async and package:stack_trace)
Image provider:
NetworkImage("https://i0.wp.com/www.dignited.com/wp-content/uploads/2012/09/Magazine-QR-Code.jpg?fit=500%2C404&ssl=1",
scale: 1.0)
Image configuration: ImageConfiguration()
Image key:
NetworkImage("https://i0.wp.com/www.dignited.com/wp-content/uploads/2012/09/Magazine-QR-Code.jpg?fit=500%2C404&ssl=1",
scale: 1.0)
════════════════════════════════════════════════════════════════════════════════════════════════════
The pixelColorAt() function has been tested previously using ui.Image objects and works as expected. I'm just trying to get the class to work with ImageProvider constructor variables rather than ui.Image.

Answer 1

Just look at the source code:
ImageConfiguration createLocalImageConfiguration(BuildContext context, { Size size }) {
return ImageConfiguration(
bundle: DefaultAssetBundle.of(context),
devicePixelRatio: MediaQuery.of(context, nullOk: true)?.devicePixelRatio ?? 1.0,
locale: Localizations.localeOf(context, nullOk: true),
textDirection: Directionality.of(context),
size: size,
platform: defaultTargetPlatform,
);
}
Thus, as long as you provide those things like bundle, devicePixelRatio, etc, manually, then you can happily create the ImageConfiguration.
Actually some parts can be null. For example, locale: Localizations.localeOf(context, nullOk: true) has nullOk: true. Thus you can simply write ImageConiguration(locale: null, ...). Other parts are similar.
In conclusion, write a method like:
ImageConfiguration myOwnCreateLocalImageConfigurationWithoutBuildContext() {
return ImageConfiguration(
bundle: maybenullorsomething,
devicePixelRatio: 1.0,
locale: null,
textDirection: Directionality.ltr, // or something you like
size: null,
platform: defaultTargetPlatform,
);
}

Answer 2

why don't just create default one?
imageProvider.resolve(const ImageConfiguration())