如何使用列表大小与Room数据库返回的列表大小不同的AAC分页库 [英] How to use AAC paging library with list size different than list size returned by Room database

问题描述

我正在尝试使用新的 Paging Library 和 Room 作为数据库，但是我遇到了一个问题，即由数据库不应该是发送到UI的相同列表，我先将一些实体 map 展示给用户，然后在此 map 操作中更改列表的大小(添加项目)，显然 Paging Library 不支持这种操作，因为当我尝试运行该应用程序时，出现了以下异常:

I'm trying to use the new Paging Library and Room as database but I'm facing a problem, the PagedList returned by the database is not supposed to be the same list sent to the UI, I map some entities before showing it to the user and during this map operation I change the list size (add items), apparently the Paging Library doesn't support this kind of operation because when I try to run the app I get this exception:

Caused by: java.lang.IllegalStateException: Invalid Function 'function_name' changed return size. This is not supported.

查看分页库源代码，您会看到以下方法:

Looking at the paging library source code you see this method:

static <A, B> List<B> convert(Function<List<A>, List<B>> function, List<A> source) {
    List<B> dest = function.apply(source);
    if (dest.size() != source.size()) {
        throw new IllegalStateException("Invalid Function " + function
            + " changed return size. This is not supported.");
    }
    return dest;
}

在将动态项目添加到 PagedList 之前，是否有解决方法或需要处理的事情?

Is there a workaround or something for dealing with when you add dynamic items to the PagedList before using it?

这就是我正在做的

DAO

@Query("SELECT * FROM table_name")
fun getItems(): DataSource.Factory<Int, Item>

LocalSource

LocalSource

fun getItems(): DataSource.Factory<Int, Item> {
    return database.dao().getItems()
        .mapByPage { map(it) } // This map operation changes the list size
}

推荐答案

我想我已经找到了解决方案..

I think I've found a solution..

尽管这是一种解决方法，但对我来说却是有效的.

Although it's a workaround it worked for me.

就我而言，我试图为这样的名称创建一个按字母顺序划分的列表:

In my case, I was trying to create an alphabet sectioned list for a names like this:

**A - HeaderItem**
Aaron - Item
Anny - Item
**B - HeaderItem**
Bob - Item
Bil
**C - HeaderItem**
....

ROOM中的项目当然只是名称，当我尝试映射分页的项目并添加节标题时，它会更改列表大小，并且出现相同的错误.

The items in ROOM are only the names of course, when I am trying to map the paged items and add the sections headers it change the list size and I am getting the same error.

我所做的是，HeaderItem对象包装了一个这样的Item:

What I did is, the HeaderItem object wraps an Item like this:

首先，所有Item都实现了ListItem接口

First, all Items are implementing the ListItem interface

interface ListItem{
 const val HEADER = 0
 const val ITEM = 1
 fun getItemType() : Int
}

然后标题项目如下所示

class HeaderItem(val headerTitle : String, val item : Item) : ListItem {
  @override
  fun getItemType() : Int {
    return ListItem.HEADER
  }
}

然后，当我映射项目时，添加HeaderItem时，它将包含一个Item，这样映射的PagedList大小就不会改变.现在我没有得到这个例外.

Then when I map the items, when adding a HeaderItem, it takes an Item in it, this way the mapped PagedList size doesn't change. Now I am not getting this exception.

但是，这创建了一些额外的工作，因为我必须显式地设置HeaderItem装饰，并且还要在适配器中进行设置，在绑定标题项时，我必须注意内部Item及其所有逻辑，例如单击侦听器等.

However, This creates some additional work as I had to set the HeaderItem decoration explicitly and also in the adapter, when bind the header item I had to take care the internal Item + all its logic such as click listeners etc'.

如果能支持开箱即用的列表大小更改，我会很高兴.

I will be happy if there will be support for changes in the list size out of the box.

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