Flutter Error: Invalid argument(s): No host specified in URI file:///null

Question

我想从 Firebase 实时数据库访问我的图像。但我还没有将图像保存在 Db 上，所以它应该显示默认图像，但相反，我得到了这张蓝色图像，它与 Welcome Back Hania 一起显示。我收到这张图片：

我的 Db 还没有图像 URL:

所以如果没有 URL 保存在数据库中，它应该像这样显示我的默认图像：

我在 Future 函数中获取图像的代码是：

Future<String> getPicture() async {
    User cuser = await firebaseAuth.currentUser;
    return ref.child('User_data').child(cuser.uid).once().then((DataSnapshot snap) {
      return snap.value['profile_photo'].toString();
    });
  }

Future Builder 用于从数据库获取图像的代码：

 Container(
                alignment: Alignment.centerRight,
                width: size.width,
                padding: EdgeInsets.symmetric(horizontal: 33),
                child: CircleAvatar(
                  radius: 46,
                  backgroundColor: Colors.white,
                  child: FutureBuilder(
                    future: getPicture(),
                    builder: (context, snapshot) {
                      if (snapshot.hasData) {
                        return CircleAvatar(
                          radius: 40,
                          backgroundImage: NetworkImage(snapshot.data),
                        );
                      } else {
                        return CircleAvatar(
                            radius: 40,
                            backgroundImage:
                                AssetImage("assets/images/avatar.jpg"));
                      }
                    },
                  ),
                ),
              ),

我会在编辑USer的个人资料时存储图片，暂时不添加。那么我的错误的解决方案是什么。请帮助我，因为我是 Flutter 的新手

错误：

════════ Exception caught by image resource service ════════════════════════════════════════════════
The following ArgumentError was thrown resolving an image codec:
Invalid argument(s): No host specified in URI file:///null

When the exception was thrown, this was the stack: 
#0      _HttpClient._openUrl (dart:_http/http_impl.dart:2425:9)
#1      _HttpClient.getUrl (dart:_http/http_impl.dart:2346:48)
#2      NetworkImage._loadAsync (package:flutter/src/painting/_network_image_io.dart:89:59)
#3      NetworkImage.load (package:flutter/src/painting/_network_image_io.dart:50:14)
#4      ImageProvider.resolveStreamForKey.<anonymous closure> (package:flutter/src/painting/image_provider.dart:503:13)
...
Image provider: NetworkImage("null", scale: 1.0)
Image key: NetworkImage("null", scale: 1.0)
════════════════════════════════════════════════════════════════════════════════════════════════════

Answer 1

问题出在这一行：

return snap.value['profile_photo'].toString();

由于 snap.value['profile_photo'] 是 null，因此 null.toString() 导致“null” - null 的字符串值。

你需要做的是稍微调整一下这个语句：

return snap.value['profile_photo']?.toString();

现在，如果 snap.value['profile_photo'] 是 null，那么实际的 null 值将从这个未来返回，而不是它的字符串表示。

Flutter Error: Invalid argument(s): No host specified in URI file:///null

Flutter Error: Invalid argument(s): No host specified in URI file:///null

dart

firebase-realtime-database

flutter

firebase-storage