未处理的异常：类型为'Future< void>'不是“ Future< Photography>”类型的子类型在Firestore上 [英] Unhandled Exception: type 'Future<void>' is not a subtype of type 'Future<Photography>' on Firestore

问题描述

我需要从Firestore数据库中获取所有数据。
我遵循这种方式， https://stackoverflow.com/a/55865045/9139407

I need to get all the data from the firestore database. I follow this way, https://stackoverflow.com/a/55865045/9139407

 Future<Photography> getPhotography() {
  Future<Photography> data =  await db
    .collection('photography')
    .document('0yUc5QBGHNNq6WK9CyyF')
    .setData(jsonDecode(jsonEncode(Photography(
  [AllImages(["list"])],
  "image_url",
  "Shanika",
  "image_url",
  "lovely couple",
  "Bhanuka"
))));

return data;
}

错误消息是：

未处理的异常：键入'Future< void>不是
Future<类型的子类型摄影>'

Unhandled Exception: type 'Future< void >' is not a subtype of type 'Future< Photography> '

摄影模型类

import 'package:json_annotation/json_annotation.dart';
part 'Model.g.dart';

@JsonSerializable()
class Photography{
   List<AllImages> all_images;
   String couplePhoto;
   String female;
   String image_url;
   String info;
   String male;

  Photography();

  factory Photography.fromJson(Map<String, dynamic> json) => _$PhotographyFromJson(json);
   Map<String,dynamic> toJson() => _$PhotographyToJson(this);
}

@JsonSerializable()
class AllImages {
  final List<String> imageUrl;

  AllImages(this.imageUrl);

  factory AllImages.fromJson(Map<String, dynamic> json) => _$AllImagesFromJson(json);
  Map<String,dynamic> toJson() => _$AllImagesToJson(this);
}

下一个问题是，如何在bloc上添加这些数据

  Sink<Photography> get inFirestore => _firestoreController.sink;

像这样吗？但错误是，不能将参数类型'Future'分配给参数类型'摄影'

final result = db.getPhotography();
inFirestore.add(result);

推荐答案

Document.setData（） 返回 Future< void> -表示将来完成时不会返回任何数据。这当然对二传手来说是合理的。这就是为什么您无法将其变成任何东西的原因。目前尚不清楚您打算从何处获取数据。您从一个空的（？）摄影开始，对其进行编码，解码并存储，然后期望返回某些内容。什么？原来的空物体？ （您可以退还-但我认为那不是您想要的。）

Document.setData() returns a Future<void> - meaning that when it completes in the future it won't return any data. That's reasonable for a setter of course. That's why you can't turn it into anything. It's not clear where you intend to get data from. You start with an empty(?) Photography, encode it, decode it, and store it then expect to return something. What? The original empty object? (You could just return that - but I don't think that's what you want.)

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