包含 headers 部分的 RealmBaseAdapter

Question

我正在尝试为 Android 使用 realm 数据存储，并且我正在尝试构建一个应用程序向用户显示 ListView 中的选项列表，有点像用户联系人列表。每个部分（如 A、B、C 等）的首字母应为 header。有没有办法用 RealmBaseAdapter 来实现这个？

目前我正在使用它 ArrayAdapter 并且我只是有一个填充了值的数组，但如果可能的话，我想使用它的适配器从 Realm 中提取数据。我知道在 iOS 中使用 NSFetchedResultsController 非常简单。我们如何将 RealmResults 分成几个部分？

Answer 1

RealmBaseAdapter 不能与 ExpandableListAdapter 一起使用（我假设您正在使用它来创建部分？），所以现在您唯一的选择是创建您自己的实现。但是 RealmResults 也是一个列表，因此它应该可以与 ArrayAdapter 无缝协作。

您还可以在此处查看更多详细信息：https://github.com/realm/realm-java/issues/978

Answer 2

这是我用的：

package com.poterion.android.library.adapters

import android.widget.BaseExpandableListAdapter
import io.realm.*

/**
 * @author Jan Kubovy &lt;jan@kubovy.eu&gt;
 */
abstract class RealmExpandableListAdapter<out Group : Any, Item : RealmModel>(
        private val itemGroupsProvider: (Item) -> Collection<Group?>,
        private val groupsProvider: (Collection<Item>) -> List<Group?>,
        private var adapterData: OrderedRealmCollection<Item>?) : BaseExpandableListAdapter() {
    private val listener: RealmChangeListener<OrderedRealmCollection<Item>>?

    protected val groups: List<Group?>
        get() {
            return adapterData?.takeIf { isDataValid }?.let(groupsProvider) ?: emptyList()
        }

    private val isDataValid: Boolean
        get() = adapterData?.isValid == true

    init {
        if (adapterData?.isManaged == false)
            throw IllegalStateException("Only use this adapter with managed list, for un-managed lists you can just use the BaseAdapter")
        this.listener = RealmChangeListener { notifyDataSetChanged() }
        adapterData?.takeIf { isDataValid }?.also { addListener(it) }
    }

    private fun addListener(data: OrderedRealmCollection<Item>) {
        when (data) {
            is RealmResults<Item> -> data.addChangeListener((listener as RealmChangeListener<RealmResults<Item>>))
            is RealmList<Item> -> data.addChangeListener((listener as RealmChangeListener<RealmList<Item>>))
            else -> throw IllegalArgumentException("RealmCollection not supported: " + data.javaClass)
        }
    }

    private fun removeListener(data: OrderedRealmCollection<Item>) {
        when (data) {
            is RealmResults<Item> -> data.removeChangeListener((listener as RealmChangeListener<RealmResults<Item>>))
            is RealmList<Item> -> data.removeChangeListener((listener as RealmChangeListener<RealmList<Item>>))
            else -> throw IllegalArgumentException("RealmCollection not supported: " + data.javaClass)
        }
    }

    override fun getGroupCount(): Int = groups.size

    override fun getChildrenCount(groupPosition: Int): Int = adapterData?.takeIf { isDataValid }?.let { data ->
        val g = groups[groupPosition]
        data.filter { g == null || groups(it).contains(g) }.size
    } ?: 0

    override fun getGroup(groupPosition: Int): Group? = if (groups.size > groupPosition) groups[groupPosition] else null

    override fun getChild(groupPosition: Int, childPosition: Int): Item? = children(groupPosition)
        .takeIf { it.size > childPosition }?.get(childPosition)

    override fun notifyDataSetChanged() {
        super.notifyDataSetChanged()
    }

    private fun children(groupPosition: Int): List<Item> {
        return getGroup(groupPosition)
                    ?.let { g -> adapterData?.takeIf { isDataValid }?.filter { groups(it).contains(g) } } ?: emptyList()
    }
}

和用法：

class PersonListAdapter(realm: Realm) :
        RealmExpandableListAdapter<String, Person>(
                itemGroupsProvider = { person -> arrayOf(person.group, null) },
                groupsProvider = { people -> people.map { it.group } },
                adapterData = realm.where(Person::class.java)
                        .findAllSortedAsync("lastName", Sort.ASCENDING, "firstName", Sort.ASCENDING)) {

    override fun getGroupId(groupPosition: Int) = getGroup(groupPosition).id

    override fun getChildId(groupPosition: Int, childPosition: Int) = getChild(groupPosition, childPosition).id

    override fun hasStableIds() = true

    override fun getGroupView(groupPosition: Int, isExpanded: Boolean, convertView: View?, parent: ViewGroup?): View {
        // ... Item View here ...
    }

    override fun getChildView(groupPosition: Int, childPosition: Int, isLastChild: Boolean,
                              convertView: View?, parent: ViewGroup?): View {
        // ... Group View here ...
    }

    override fun isChildSelectable(groupPosition: Int, childPosition: Int) = true
}

包含 headers 部分的 RealmBaseAdapter

RealmBaseAdapter with section headers

android

listview

realm