Question

我无法通过给定属性对可观察的RxList进行排序。当我使用BloC方法并使用一个简单的List时，排序工作正常。

最近，我将状态管理更改为GetX（https://github.com/jonataslaw/getx）程序包，因为看到了很多优点（不需要上下文，无需过渡到页面，等等）。

这里有两种情况，我很糟糕，之前没有解释，让我放入小黄瓜的

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

方案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，将触发器添加到流中后，始终按日期降序对获取的帖子列表进行重新排序，无论触发器是PullDown还是到达列表的末尾，以便始终显示项按发布顺序。

希望有人可以帮帮我。

Answer 1

首先订购您的列表，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),
      ),
    );

Answer 2

经过数天的努力，我发现它简单得多，并且由于我缺乏知识。

由于列表是可见的，仅将其转换为列表就足以完成排序：

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！

对Flutter应用程序的getX dart包中的RxList进行排序

2 个答案: