Dart Flutter 错误通过 Firebase 存储调用照片

Question

我有这样的代码：

    class MainScreen extends StatefulWidget {
      @override
      State<MainScreen> createState() => _MainScreenState();
    }
    class _MainScreenState extends State<MainScreen> {
      @override
      Widget build(BuildContext context) {
        return Column(
          children: <Widget>[
            Column(
              children: [
                Container(
                  height: 100,
                  width: 100,
                  child: FutureBuilder<String>(
                    future: downloadURLExample(),
                    builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
                      if(snapshot.hasData) 
                      return Image.network(snapshot.data);
                    }
                  ),
                ),
                SizedBox(height: 10),
                Text(
                  "Hello",
                  style: TextStyle(
                    fontSize: 20,
                    fontWeight: FontWeight.bold,
                    color: Colors.white,
                  ),
                ),
              ],
            ),
          ] 
        );
      }
    }
  Future<String> downloadURLExample() {
    var downloadURL = FirebaseStorage.instance.ref('defaultProfilePhoto.png').getDownloadURL();
    return downloadURL;
  }

我的目标是在应用中显示我上传到 Firebase Storage 的照片。 Firebase 存储：

当我运行代码时，它会将我重定向到 debug.dart.

的 throw FlutterError.fromParts(<DiagnosticsNode>[ 代码行

还有控制台：

════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building FutureBuilder<String>(dirty, state: _FutureBuilderState<String>#a8e50):
A build function returned null.

The offending widget is: FutureBuilder<String>
Build functions must never return null.

To return an empty space that causes the building widget to fill available room, return "Container()". To return an empty space that takes as little room as possible, return "Container(width: 0.0, height: 0.0)".

The relevant error-causing widget was
FutureBuilder<String>
When the exception was thrown, this was the stack
#0      debugWidgetBuilderValue.<anonymous closure>
#1      debugWidgetBuilderValue
#2      ComponentElement.performRebuild
#3      StatefulElement.performRebuild
#4      Element.rebuild
#5      ComponentElement._firstBuild
#6      StatefulElement._firstBuild
#7      ComponentElement.mount
...     Normal element mounting (10 frames)
#17     Element.inflateWidget
#18     MultiChildRenderObjectElement.inflateWidget
#19     MultiChildRenderObjectElement.mount
#20     Element.inflateWidget
#21     MultiChildRenderObjectElement.inflateWidget
#22     MultiChildRenderObjectElement.mount
...     Normal element mounting (198 frames)
#220    Element.inflateWidget
#221    MultiChildRenderObjectElement.inflateWidget
#222    MultiChildRenderObjectElement.mount
...     Normal element mounting (126 frames)
#348    Element.inflateWidget
#349    MultiChildRenderObjectElement.inflateWidget
#350    MultiChildRenderObjectElement.mount
...     Normal element mounting (45 frames)
#395    Element.inflateWidget
#396    MultiChildRenderObjectElement.inflateWidget
#397    MultiChildRenderObjectElement.mount
...     Normal element mounting (15 frames)
#412    Element.inflateWidget
#413    MultiChildRenderObjectElement.inflateWidget
#414    MultiChildRenderObjectElement.mount
...     Normal element mounting (206 frames)
#620    Element.inflateWidget
#621    MultiChildRenderObjectElement.inflateWidget
#622    MultiChildRenderObjectElement.mount
...     Normal element mounting (362 frames)
#984    Element.inflateWidget
#985    Element.updateChild
#986    RenderObjectToWidgetElement._rebuild
#987    RenderObjectToWidgetElement.mount
#988    RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure>
#989    BuildOwner.buildScope
#990    RenderObjectToWidgetAdapter.attachToRenderTree
#991    WidgetsBinding.attachRootWidget
#992    WidgetsBinding.scheduleAttachRootWidget.<anonymous closure>
(elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)
════════════════════════════════════════════════════════════════════════════════
Restarted application in 2.960ms.
W/DynamiteModule( 7575): Local module descriptor class for com.google.android.gms.providerinstaller.dynamite not found.
I/DynamiteModule( 7575): Considering local module com.google.android.gms.providerinstaller.dynamite:0 and remote module com.google.android.gms.providerinstaller.dynamite:0
W/ProviderInstaller( 7575): Failed to load providerinstaller module: No acceptable module com.google.android.gms.providerinstaller.dynamite found. Local version is 0 and remote version is 0.
W/ProviderInstaller( 7575): Failed to report request stats: com.google.android.gms.common.security.ProviderInstallerImpl.reportRequestStats [class android.content.Context, long, long]
W/ConnectivityManager.CallbackHandler( 7575): callback not found for CALLBACK_AVAILABLE message
W/NetworkRequest( 7575): No App Check token for request.

我的目标是在 Flutter 应用程序中显示我上传到 Firebase Storage 的图像。我怎么解决这个问题？在此先感谢您的帮助。

Answer 1

我认为问题出在这里：

builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
  if(snapshot.hasData) 
    return Image.network(snapshot.data);
}

您需要 return 一些东西，即使快照还没有数据（还）。例如：

builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
  if(snapshot.hasData) 
    return Image.network(snapshot.data);
  return CircularProgressIndicator(); // 
}

Dart Flutter 错误通过 Firebase 存储调用照片

Dart Flutter Error calling photo via Firebase Storage

android

firebase

flutter

firebase-storage