java - 如何按 id 对 ArrayList 进行排序并添加到 ArrayList ArrayList>

Question

我有带有值的 mList2。存在具有相同 id 的值。如何获取具有相同 id 的对象分组的 List 或 ArrayList 并将其添加到 ArrayList>？

List<ProfileActivity.DataPost> mList2 = list;
    List<List<ProfileActivity.DataPost>> output = new ArrayList<List<ProfileActivity.DataPost>>();
    List<ProfileActivity.DataPost> itemsAlreadyGrouped = new ArrayList<ProfileActivity.DataPost>();
    for (int i = 0; i < mList2.size(); i++) {
        List<ProfileActivity.DataPost> groupList = new ArrayList<ProfileActivity.DataPost>();
        boolean groupCandidateFound = false;
        if (!itemsAlreadyGrouped.contains(mList2.get(i))) {
            for (int j = 0; j < mList2.size(); j++) {
                if (mList2.get(i).getIds_post().equals(mList2.get(j).getIds_post())) {
                    groupList.add(mList2.get(i));
                    groupCandidateFound = true;
                }
            }
            if (groupCandidateFound) {
                itemsAlreadyGrouped.add(mList2.get(i));
            }
        }
        if (groupList.size() > 0) {
            output.add(groupList);
        }
    }

    //Let's test the logic
    for (List<ProfileActivity.DataPost> group : output) {
        System.out.println(group);
        Toast.makeText(context, group.toString(),Toast.LENGTH_SHORT ).show();
    }

DataPost

data class DataPost(var text:String? = null, var photo:String? = null,
                     var type:String = "",
                     var ids_post:String = "", var position:String? = null)

Answer 1

让你的ProfileActivity.DataPost类implements Comparable<ProfileActivity.DataPost>接口(interface)，实现compareTo(ProfileActivity.DataPost o)方法

@Override
public void compareTo(ProfileActivity.DataPost o){
    return getIds_post().compareTo(o.getIds_post());
}

然后只需调用 Collections.sort(list)