无法在首次构建时加载资产，但会在热重启Flutter时加载

Question

当我第一次在模拟器或真实设备上启动应用程序八时，出现此错误：

flutter: ══╡ EXCEPTION CAUGHT BY IMAGE RESOURCE SERVICE ╞════════════════════════════════════════════════════
flutter: The following assertion was thrown resolving an image codec:
flutter: Unable to load asset: assets/New alert button.png
flutter:
flutter: When the exception was thrown, this was the stack:
flutter: #0      PlatformAssetBundle.load (package:flutter/src/services/asset_bundle.dart:221:7)
flutter: <asynchronous suspension>
flutter: #1      AssetBundleImageProvider._loadAsync (package:flutter/src/painting/image_provider.dart:484:44)
flutter: #2      AssetBundleImageProvider.load (package:flutter/src/painting/image_provider.dart:469:14)
flutter: #3      ImageProvider.resolve.<anonymous closure>.<anonymous closure>.<anonymous closure> (package:flutter/src/painting/image_provider.dart:327:17)
flutter: #4      ImageCache.putIfAbsent (package:flutter/src/painting/image_cache.dart:160:22)
flutter: #5      ImageProvider.resolve.<anonymous closure>.<anonymous closure> (package:flutter/src/painting/image_provider.dart:325:84)
flutter: (elided 13 frames from package dart:async)
flutter:
flutter: Image provider: AssetImage(bundle: null, name: "assets/New alert button.png")
flutter: Image key: AssetBundleImageKey(bundle: PlatformAssetBundle#3cb5b(), name: "assets/New alert
flutter:   button.png", scale: 1.0)
flutter: ════════════════════════════════════════════════════════════════════════════════════════════════════
flutter: Another exception was thrown: Unable to load asset: assets/New route button.png
flutter: Another exception was thrown: Unable to load asset: assets/Center map button.png

阅读与该问题相关的其他帖子（不同的解决方案建议使用不同的方式）我尝试了不同的缩进，所以我都尝试了两种方法：

flutter:
  uses-material-design: true
  assets:
  - assets/

和

flutter:
  uses-material-design: true
  assets:
    - assets/

但没有任何变化。如果执行热重启，则将正确加载资产。 我遇到的另一个问题，或者可能是真正潜在问题的暗示，是如果我将图像从IDE拖放到资产文件夹中，则会出现错误：

这是使用资产的一个按钮：

IconButton(
                        icon: Image.asset('assets/Center map button.png'),
                        iconSize: 60,
                        onPressed: () {
                          print('Center map button pressed');
                          _mapController.move(userLocation, 16);
                        }),

峡谷发现我在做什么错？ 一如既往，非常感谢您的时间和帮助。