何为分页缓存?
顾名思义,分页缓存就是边分页边缓存,分页通常使用下拉刷新控件实现,而缓存通常说的是指磁盘缓存,即保存到数据库中,数据库本身也是一个索引文件。
为什么缓存还要分页?
在很大一部分场景下,缓存都是需要分页的,不要问我为什么,问就是不懂规矩,哈哈。你家的接口一次性把整张表的数据全部都返回给你吗?先不说用户耗多少流量的问题,如果大家都一次性把表的数据都给你,那爬虫何以生存?分分钟就把你的数据全都弄走了,要知道,互联网世界,数据就是资源,数据就是钱啊!
怎么使用下拉刷新分页?
重复的问题不会再讲,看我之前的文章Android低代码开发 - 直接创建一个下拉刷新列表界面。下拉刷新和上拉加载都是用来分页加载数据的。下拉刷新往往只加载第一页的数据,而上拉加载则是加载下一页的数据,如果有。
下拉刷新怎么和缓存结合起来?
这个问题问的好。本篇提到的缓存一律指数据库缓存,而非内存缓存。当然我的dcache库https://github.com/dora4/dcache-android 支持内存缓存,会简单带过。我以缓存系统通知列表为例。
package com.dorachat.dorachat.repository
import android.content.Context
import com.dorachat.dorachat.common.AppConfig.Companion.PRODUCT_NAME
import com.dorachat.dorachat.http.ApiResult
import com.dorachat.dorachat.http.service.HomeService
import com.dorachat.dorachat.model.SystemNotification
import dora.cache.data.adapter.ListResultAdapter
import dora.cache.data.fetcher.OnLoadStateListener
import dora.cache.factory.DatabaseCacheHolderFactory
import dora.cache.repository.DoraPageDatabaseCacheRepository
import dora.cache.repository.ListRepository
import dora.http.DoraListCallback
import dora.http.retrofit.RetrofitManager.getService
import retrofit2.Callback
import javax.inject.Inject
@ListRepository
class SysNotificationRepository @Inject constructor(context: Context) :
DoraPageDatabaseCacheRepository<SystemNotification>(context) {
override fun onLoadFromNetwork(
callback: DoraListCallback<SystemNotification>,
listener: OnLoadStateListener?
) {
getService(HomeService::class.java).getSystemNotificationList(PRODUCT_NAME)
.enqueue(ListResultAdapter<SystemNotification, ApiResult<SystemNotification>>(callback)
as Callback<ApiResult<MutableList<SystemNotification>>>)
}
override fun createCacheHolderFactory(): DatabaseCacheHolderFactory<SystemNotification> {
return DatabaseCacheHolderFactory(SystemNotification::class.java)
}
}
缓存仓库,使用@ListRepository标记缓存的数据结构是列表类型的。使用咱们的DoraPageDatabaseCacheRepository,进行分页数据的缓存。如果你不使用框架内置的ORM框架,则需要先整合你的ORM框架,具体看我专栏的其他文章。这个类就是为了告诉框架,你要缓存的数据结构是一个List类型的SystemNotification,而且会一页一页给到,请帮我缓存好了。我们知道list模式的BaseRepository使用流程是,先在activity设置一个数据监听器,repository.getListLiveData().observe(this, observer),然后改变一下参数,repository.setXxx(),调用一下repository.fetchListData()。一旦调用抓取数据的函数,就会调用onLoadFromNetwork()方法,加载最新参数的数据,这边的数据监听器就会被回调,同时将数据缓存一份到数据库中,以备无网络的时候使用。附上DoraPageDatabaseCacheRepository的源码你就明白了。
package dora.cache.repository
import android.content.Context
import android.util.Log
import androidx.lifecycle.LifecycleOwner
import androidx.recyclerview.widget.RecyclerView
import dora.cache.data.fetcher.OnLoadStateListener
import dora.db.builder.Condition
import dora.db.builder.QueryBuilder
import dora.db.table.OrmTable
abstract class DoraPageDatabaseCacheRepository<T : OrmTable>(context: Context)
: DoraDatabaseCacheRepository<T>(context) {
private var pageNo: Int = 0
private var pageSize: Int = 10
fun getPageNo(): Int {
return pageNo
}
fun getPageSize(): Int {
return pageSize
}
fun isLastPage(totalSize: Int) : Boolean {
val lastPage = if (totalSize % pageSize == 0) totalSize / pageSize - 1 else totalSize / pageSize
return lastPage == pageNo
}
fun observeData(owner: LifecycleOwner, adapter: AdapterDelegate<T>) {
getListLiveData().observe(owner) {
if (pageNo == 0) {
adapter.setList(it)
} else {
adapter.addData(it)
}
}
}
interface AdapterDelegate<T> {
fun setList(data: MutableList<T>)
fun addData(data: MutableList<T>)
}
/**
* 下拉刷新回调,可结合[setPageSize]使用。
*/
fun onRefresh(listener: OnLoadStateListener) {
pageNo = 0
fetchListData(listener = listener)
}
/**
* 下拉刷新高阶函数,可结合[setPageSize]使用。
*/
@JvmOverloads
fun onRefresh(block: ((Boolean) -> Unit)? = null) {
pageNo = 0
fetchListData(listener = object : OnLoadStateListener {
override fun onLoad(state: Int) {
block?.invoke(state == OnLoadStateListener.SUCCESS)
}
})
}
/**
* 上拉加载回调,可结合[setPageSize]使用。
*/
fun onLoadMore(listener: OnLoadStateListener) {
pageNo++
fetchListData(listener = listener)
}
/**
* 上拉加载高阶函数,可结合[setPageSize]使用。
*/
@JvmOverloads
fun onLoadMore(block: ((Boolean) -> Unit)? = null) {
pageNo++
fetchListData(listener = object : OnLoadStateListener {
override fun onLoad(state: Int) {
block?.invoke(state == OnLoadStateListener.SUCCESS)
}
})
}
open fun setPageSize(pageSize: Int): DoraPageDatabaseCacheRepository<T> {
this.pageSize = pageSize
return this
}
open fun setCurrentPage(pageNo: Int, pageSize: Int): DoraPageDatabaseCacheRepository<T> {
this.pageNo = pageNo
this.pageSize = pageSize
return this
}
override fun query(): Condition {
val start = pageNo * pageSize
return QueryBuilder.create()
.limit(start, pageSize)
.toCondition()
}
/**
* 没网的情况下直接加载缓存数据。
*/
override fun selectData(ds: DataSource): Boolean {
var isLoaded = false
if (!isNetworkAvailable) {
isLoaded = ds.loadFromCache(DataSource.CacheType.DATABASE)
}
return if (isNetworkAvailable) {
try {
ds.loadFromNetwork()
true
} catch (e: Exception) {
Log.e(TAG, e.toString())
isLoaded
}
} else isLoaded
}
}
在这个分页缓存仓库类中,定义了分页的一些参数,如第几页?每页几条数?onRefresh()和onLoadMore()完全就是为了配合下拉刷新控件而设计的。不会使用dcache库的,是不是看源码也能知道怎么调用?observeData()方法是不是就是我们刚才讲到的数据监听器,或者说观察者。那么就来看一下调用层面的代码吧。
package com.dorachat.dorachat.ui.activity.admin
import android.app.Activity
import android.content.Intent
import android.os.Build
import android.os.Bundle
import androidx.annotation.RequiresApi
import com.dorachat.dorachat.ChatApp
import com.dorachat.dorachat.R
import com.dorachat.dorachat.common.AppConfig.Companion.ACTION_UPDATE_SYS_NOTIFICATION
import com.dorachat.dorachat.common.AppConfig.Companion.PRODUCT_NAME
import com.dorachat.dorachat.common.AppConfig.Companion.REQUEST_CODE_ADD_SYS_NOTIFICATION
import com.dorachat.dorachat.common.AppConfig.Companion.REQUEST_CODE_UPDATE_SYS_NOTIFICATION
import com.dorachat.dorachat.common.IntentKeys.Companion.KEY_SYSTEM_NOTIFICATION
import com.dorachat.dorachat.databinding.ActivitySysNotificationBinding
import com.dorachat.dorachat.di.component.DaggerUserComponent
import com.dorachat.dorachat.http.service.HomeService
import com.dorachat.dorachat.model.SystemNotification
import com.dorachat.dorachat.model.request.ReqSysNotification
import com.dorachat.dorachat.repository.SysNotificationRepository
import com.dorachat.dorachat.ui.adapter.SysNotificationAdapter
import dora.cache.repository.DoraPageDatabaseCacheRepository
import dora.dagger.DaggerBaseActivity
import dora.http.DoraHttp
import dora.http.DoraHttp.net
import dora.http.retrofit.RetrofitManager
import dora.util.IntentUtils
import dora.util.ViewUtils
import dora.widget.DoraAlertDialog
import dora.widget.Tips
import dora.widget.pull.SwipeLayout
import javax.inject.Inject
class SysNotificationActivity : DaggerBaseActivity<ActivitySysNotificationBinding>() {
@Inject lateinit var notificationRepository: SysNotificationRepository
private val adapter = SysNotificationAdapter()
override fun getLayoutId(): Int {
return R.layout.activity_sys_notification
}
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
super.onActivityResult(requestCode, resultCode, data)
if (resultCode == Activity.RESULT_OK) {
if (requestCode == REQUEST_CODE_ADD_SYS_NOTIFICATION ||
requestCode == REQUEST_CODE_UPDATE_SYS_NOTIFICATION) {
notificationRepository.onRefresh()
}
}
}
override fun onInjectDaggerComponent() {
DaggerUserComponent.builder().appComponent(ChatApp.appComponent).build().inject(this)
}
@RequiresApi(Build.VERSION_CODES.O)
override fun initData(savedInstanceState: Bundle?, binding: ActivitySysNotificationBinding) {
binding.tvSysNotificationAdd.setOnClickListener {
IntentUtils.startActivityForResult(SysNotificationEditorActivity::class.java, REQUEST_CODE_ADD_SYS_NOTIFICATION)
}
notificationRepository.observeData(this, object : DoraPageDatabaseCacheRepository.AdapterDelegate<SystemNotification> {
override fun addData(data: MutableList<SystemNotification>) {
adapter.addData(data)
mBinding.emptyLayout.showContent()
}
override fun setList(data: MutableList<SystemNotification>) {
adapter.setList(data)
mBinding.emptyLayout.showContent()
}
})
binding.slSysNotificationList.setOnSwipeListener(object : SwipeLayout.OnSwipeListener {
override fun onRefresh(swipeLayout: SwipeLayout) {
}
override fun onLoadMore(swipeLayout: SwipeLayout) {
if (!notificationRepository.isLastPage(notificationRepository.getTotalSize())) {
notificationRepository.onLoadMore {
swipeLayout.loadMoreFinish(if (it) SwipeLayout.SUCCEED else SwipeLayout.FAIL)
}
}
}
})
ViewUtils.configRecyclerView(binding.recyclerView).adapter = adapter
notificationRepository.onRefresh()
adapter.addChildClickViewIds(R.id.ll_sys_notification_list, R.id.btn_delete)
adapter.setOnItemChildClickListener { _, view, position ->
when (view.id) {
R.id.ll_sys_notification_list -> {
val item = adapter.getItem(position)
IntentUtils.startActivityForResultWithSerializable(this@SysNotificationActivity,
SysNotificationEditorActivity::class.java,
ACTION_UPDATE_SYS_NOTIFICATION,
REQUEST_CODE_UPDATE_SYS_NOTIFICATION,
KEY_SYSTEM_NOTIFICATION, item)
}
R.id.btn_delete -> {
DoraAlertDialog(this).show(R.string.confirm_delete) {
themeColorResId(R.color.colorPrimary)
positiveListener {
val item = adapter.getItem(position)
net {
val req = ReqSysNotification(
productName = PRODUCT_NAME,
id = item.id
)
val ok = DoraHttp.result {
RetrofitManager.getService(HomeService::class.java)
.removeSystemNotification(req.toRequestBody())
}?.data
if (ok == true) {
adapter.removeAt(position)
Tips.showSuccess(R.string.deleted_successfully)
}
}
}
}
}
}
}
}
}
这里用到了Dagger的依赖注入,不在本篇的讨论范围。DoraPageDatabaseCacheRepository.AdapterDelegate告诉适配器,你就在我的回调里面更新数据就好了。
在哪里去找缓存库相关源码?
https://github.com/dora4/dcache-android 缓存库
https://github.com/dora4/dview-swipe-layout 下拉刷新控件
https://github.com/dora4/dview-empty-layout 空态页面