flutter/dart错误:参数类型'Future <File>'无法分配给参数类型'File'

Question

我正在尝试用flutter和firebase构建我的第一个移动应用程序.当我尝试显示和存储照片时,我遇到以下问题:

错误:无法将参数类型"Future"分配给参数类型"File".(argument_type_not_assignable在[whereassistant] lib/main.dart:85)

我应该做一些铸造,但我不理解hox做得恰当.

这是我的Future文件声明:

Future<File> _imageFile;

我正在拍摄一张显示在屏幕上的照片:

    setState(() {
      _imageFile = ImagePicker.pickImage(source: source);
    });

但是在尝试将照片发送到Firebase时出现错误:

    final StorageUploadTask uploadTask = ref.put(_imageFile);
    final Uri downloadUrl = (await uploadTask.future).downloadUrl;

这是我基于代码示例使用的类:

class _MyHomePageState extends State<MyHomePage> {
  Future<File> _imageFile;

  void _onImageButtonPressed(ImageSource source) async {
    GoogleSignIn _googleSignIn = new GoogleSignIn();
    var account = await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleAuth = await account.authentication;
    final FirebaseUser user = await _auth.signInWithGoogle(
      accessToken: googleAuth.accessToken,
      idToken: googleAuth.idToken,
    );
    assert(user.email != null);
    assert(user.displayName != null);
    assert(!user.isAnonymous);
    assert(await user.getIdToken() != null);

    final FirebaseUser currentUser = await _auth.currentUser();
    assert(user.uid == currentUser.uid);

    setState(() {
      _imageFile = ImagePicker.pickImage(source: source);
    });
    var random = new Random().nextInt(10000);
    var ref = FirebaseStorage.instance.ref().child('image_$random.jpg');
    final StorageUploadTask uploadTask = ref.put(_imageFile);
    final Uri downloadUrl = (await uploadTask.future).downloadUrl;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: const Text('Where Assistant'),
      ),
      body: new Center(
        child: new FutureBuilder<File>(
          future: _imageFile,
          builder: (BuildContext context, AsyncSnapshot<File> snapshot) {
            debugPrint('test recup image');
            print(snapshot);

            if (snapshot.connectionState == ConnectionState.done &&
                snapshot.data != null) {
              return new Image.file(snapshot.data);
            } else if (snapshot.error != null) {
              return const Text('Error picking image.');
            } else {
              return const Text('No image so far.');
            }
          },
        ),
      ),
      floatingActionButton: new Column(
        mainAxisAlignment: MainAxisAlignment.end,
        children: <Widget>[
          new FloatingActionButton(
            onPressed: () => _onImageButtonPressed(ImageSource.gallery),
            tooltip: 'Pick an image from gallery',
            child: new Icon(Icons.photo_library),
          ),
          new Padding(
            padding: const EdgeInsets.only(top: 16.0),
            child: new FloatingActionButton(
              onPressed: () => _onImageButtonPressed(ImageSource.camera),
              tooltip: 'Take a Photo',
              child: new Icon(Icons.camera_alt),
            ),
          ),
        ],
      ),
    );
  }
}

Answer 1

ref.put请求一个Fileas参数.你传递的是一个Future<File>.

您需要等待未来的结果才能拨打电话.

您可以将代码更改为

final StorageUploadTask uploadTask = ref.put(await _imageFile);
final Uri downloadUrl = (await uploadTask.future).downloadUrl;

或_imageFile改为File而不是Future<File>