对 Flutter 应用程序的 getX dart 包中的 RxList 进行排序

Question

我无法按给定属性对可观察的 RxList 进行排序。当我使用 BloC 方法时，排序工作正常，使用一个简单的列表。

最近我将状态管理更改为 GetX (https://github.com/jonataslaw/getx) 包，因为我看到了几个优点（不需要上下文、转换到页面等）。

这里有两个场景，我的不好，前面没有解释，我放小黄瓜的

场景 1：

Given user in Posts Screen
When user Pull down to get Newest posts
Then user get the newly fetched posts on top of the previous loaded list

场景 2：

Given user in Posts Screen
When user reaches the end of the list
Then user get more posts at the end of the previous loaded list

post_model.dart

class Post {
  final int id;
  final String title;
  final DateTime date;
  final User user;

Post({
    @required this.id,
    @required this.title,
    @required this.date,
    this.user});
 
}

post_controller.dart

import 'dart:async';

import 'package:get/state_manager.dart';
import 'package:blog/models/post.dart';
import 'package:blog/services/posts_api.dart';

class PostsController extends GetxController {
  int _page = 0;

  ---------HERE OBS LIST-----------
  RxList posts = [].obs;

  @override
  void onReady() {
    super.onReady();
    this.loadPosts();
  }

  Future<void> loadPosts({isRefreshLoad = false}) async {
    int pager;
    if (isRefreshLoad) {
      pager = 1;
    } else {
      increment();
      pager = this._page;
    }

    Map<String, String> arguments = {'page': '$pager'};
    final List<Post> newPosts =
        await PostsApi.instance.getPosts(arguments: arguments);

    // remove duplicates
    posts.addAll(
      newPosts.where(
        (newPosts) => posts.every((post) => newPosts.id != post.id),
      ),
    );

    //----------HERE'S THE EXCEPTION----------
    posts.sort((a, b) => b.id.compareTo(a.id));
    update(['posts']);
  }
}

错误

flutter: [GETX] PostsController has been initialized
[VERBOSE-2:ui_dart_state.cc(166)] Unhandled Exception: type 'Post' is not a subtype of type 'List<dynamic>'
#0      RxList.remove 
package:get/…/rx/rx_impl.dart:333

PostsScreen.dart

Scaffold(
                backgroundColor: Color.fromRGBO(58, 66, 86, 1.0),
                appBar: AppBarWidget(
                  drawerOpen: drawerPosition,
                  appBarVisible: _isVisible,
                  drawerVisible: true,
                ),
                body: ColorfulSafeArea(
                  overflowRules: OverflowRules.only(left: true, bottom: true),
                  child: GetBuilder<PostsController>(
                    id: 'posts',
                    init: PostsController(),
                    builder: (_postsController) {
                      _postsControllerGlobal = _postsController;
                      // Scenario 1 - Triggers when user pull down to get new posts
                      return RefreshIndicator( 
                        onRefresh: () {
                          return _postsController.loadPosts(
                              isRefreshLoad: true);
                        },
                        child: StreamBuilderWidget(
                          stream: _postsController.posts.stream,
                         // Scenario 2 Triggers when scroll controller reaches end of list
                          scrollController: _scrollController,                               isDrawerOpen: _isDrawerOpen,
                          widgetType: 'PostItemWidget',
                        ),
                      );
                    },
                  ),
                ),
              ),

----enter code here------

我需要一种方法，在将获取的帖子添加到流中后，始终按日期 desc 顺序重新排序获取的帖子列表，无论触发器是 PullDown 还是到达列表的最终末尾，以便始终显示项目按已发布顺序。

希望有人能帮帮我。

Answer 1

经过几天的尝试，我发现它要简单得多，而且由于我缺乏知识。

由于列表是可观察的，只需将其转换为列表即可完成排序：

普通列表

• newPosts.sort((a, b) => b.date.compareTo(a.date));

可观察列表

• newPosts.toList().sort((a, b) => b.date.compareTo(a.date));

谢谢！

Answer 2

首先订购您的清单，然后添加它

final List<Post> newPosts =
        await PostsApi.instance.getPosts(arguments: arguments);

//----------Try this---------
newPosts.sort((a, b) => b.id.compareTo(a.id));
    
// remove duplicates
    posts.addAll(
      newPosts.where(
        (newPosts) => posts.every((post) => newPosts.id != post.id),
      ),
    );