Flutter Firebase 上传多张图片

Question

上传多张图片并等待URL列表，几秒钟后图片成功加载到firestore并返回url，但在此之前future函数返回null

Future<List<dynamic>> uploadImage() async {
     _imageFile.forEach((image) async {
      String rannum = Uuid().v1();
      StorageReference reference =
          FirebaseStorage.instance.ref().child('Reviews').child(rannum);
      StorageUploadTask uploadTask = reference.putFile(image);
      StorageTaskSnapshot downloadUrl = (await uploadTask.onComplete);
      String _url = await downloadUrl.ref.getDownloadURL();
      _urllist.add(_url);
    });

    return _urllist;
  }

Answer 1

你必须像这样调用你的函数：

uploadImage(_imageFile).then((List<String> urls) => urls.forEach((element) => print(element)))

我也改变了你的功能：

Future<List<String>> uploadImage(List<File> _imageFile) async {
    List<String> _urllist = [];
    await _imageFile.forEach((image) async {
      String rannum = Uuid().v1();
      StorageReference reference =
      FirebaseStorage.instance.ref().child('Reviews').child(rannum);
      StorageUploadTask uploadTask = reference.putFile(image);
      StorageTaskSnapshot downloadUrl = await uploadTask.onComplete;
      String _url = await downloadUrl.ref.getDownloadURL();
      _urllist.add(_url);
    });

    return _urllist;
  }

我也不明白你为什么用括号括起来“await uploadTask.onComplete”