當我嘗試使用flutter_svg庫在flutter中預快取SVG檔案時出現以下錯誤：
> flutter: ══╡ EXCEPTION CAUGHT BY SVG ╞═══════════════════════════════════════════════════════════════════════
> flutter: The following _CastError was thrown resolving a single-frame picture stream:
> flutter: Null check operator used on a null value
> flutter:
> flutter: When the exception was thrown, this was the stack:
> flutter: #0 PlatformAssetBundle.load (package:flutter/src/services/asset_bundle.dart:235:39)
> flutter: #1 AssetBundle.loadString (package:flutter/src/services/asset_bundle.dart:72:33)
> flutter: #2 CachingAssetBundle.loadString.<anonymous closure> (package:flutter/src/services/asset_bundle.dart:172:56)
> flutter: #3 _LinkedHashMapMixin.putIfAbsent (dart:collection-patch/compact_hash.dart:453:23)
> flutter: #4 CachingAssetBundle.loadString (package:flutter/src/services/asset_bundle.dart:172:27)
> flutter: #5 AssetBundlePictureProvider._loadAsync (package:flutter_svg/src/picture_provider.dart:546:42)
> flutter: #6 AssetBundlePictureProvider.load (package:flutter_svg/src/picture_provider.dart:531:7)
> flutter: #7 PictureProvider.resolve.<anonymous closure>.<anonymous closure>
> (package:flutter_svg/src/picture_provider.dart:378:19)
> flutter: #8 PictureCache.putIfAbsent (package:flutter_svg/src/picture_cache.dart:91:22)
> flutter: #9 PictureProvider.resolve.<anonymous closure> (package:flutter_svg/src/picture_provider.dart:376:17)
> flutter: #10 SynchronousFuture.then (package:flutter/src/foundation/synchronous_future.dart:41:35)
> flutter: #11 PictureProvider.resolve (package:flutter_svg/src/picture_provider.dart:372:24)
> flutter: #12 precachePicture (package:flutter_svg/svg.dart:198:21)
> flutter: #13 main (package:svg_caching/main.dart:7:9)
> flutter: #14 _runMainZoned.<anonymous closure>.<anonymous closure> (dart:ui/hooks.dart:130:25)
> flutter: #19 _runMainZoned.<anonymous closure> (dart:ui/hooks.dart:126:5)
> flutter: #20 _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:297:19)
> flutter: (elided 5 frames from class _RawReceivePortImpl and dart:async)
> flutter:
> flutter: Picture provider: ExactAssetPicture(name: "images/octocat.svg", bundle: null, colorFilter: null)
> flutter: Picture key: AssetBundlePictureKey(bundle: PlatformAssetBundle#868b3(), name: "images/octocat.svg",
> flutter: colorFilter: null, theme: SvgTheme(currentColor: null, fontSize: 14.0, xHeight: 7.0))
> flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
這是我正在使用的代碼：
import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
const String svgSource = 'images/octocat.svg';
Future<void> main() async {
// Trying to pre-cache here:
await precachePicture(
ExactAssetPicture(
SvgPicture.svgStringDecoderBuilder,
svgSource,
),
null);
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
const MyHomePage({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('SVG test'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
SvgPicture.asset(
svgSource,
height: 250,
),
],
),
),
);
}
}
我的 pubspec.yaml：
name: svg_caching
description: A new Flutter project.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev
version: 1.0.0 1
environment:
sdk: ">=2.16.2 <3.0.0"
dependencies:
flutter:
sdk: flutter
cupertino_icons: ^1.0.2
flutter_svg: ^1.0.3
dev_dependencies:
flutter_test:
sdk: flutter
flutter_lints: ^1.0.0
flutter:
uses-material-design: true
assets:
- images/
顫振醫生輸出：
[?] Flutter (Channel stable, 2.10.5, on macOS 12.3.1 21E258 darwin-arm, locale en-GB)
[?] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
[?] Xcode - develop for iOS and macOS (Xcode 13.3.1)
[?] Chrome - develop for the web
[?] Android Studio (version 2021.1)
[?] IntelliJ IDEA Community Edition (version 2022.1)
[?] VS Code (version 1.66.2)
[?] HTTP Host Availability
有什么建議我可能做錯了嗎？當我不嘗試快取 SVG 檔案時，它可以正常顯示。此錯誤在 Android 和 iOS（物理設備和模擬器）上都發生。
uj5u.com熱心網友回復：
在預快取之前將此行添加到您的main()方法呼叫中：
WidgetsFlutterBinding.ensureInitialized();
轉載請註明出處，本文鏈接：https://www.uj5u.com/ruanti/475355.html