Android Page 3 Flow读sql数据库媒体文件，Kotlin
基于Kotlin的Android媒体文件浏览应用实现方案。核心功能包括：
- 使用Room数据库存储媒体文件信息（MediaEntity），并通过Paging 3库实现分页加载
- 采用Coil 3图片加载库处理媒体文件显示，配置了2GB内存和磁盘缓存
- 实现权限管理，包括读写外部存储和访问媒体文件的权限
- 采用MVVM架构，通过ViewModel管理数据，Flow进行异步数据流处理
- 使用RecyclerView展示媒体文件网格视图，支持图片和视频缩略图显示
关键技术点包括Room数据库操作、Paging分页加载、Coil图片加载以及协程处理异步任务。应用通过分页方式高效加载大量媒体文件，同时利用缓存机制提升图片加载性能。
XML
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />
<uses-permission android:name="android.permission.READ_MEDIA_VIDEO" />
XML
plugins {
id 'com.google.devtools.ksp' version '2.3.6'
}
dependencies {
implementation("io.coil-kt.coil3:coil:3.4.0")
implementation("io.coil-kt.coil3:coil-core:3.4.0")
def paging_version = "3.4.2"
implementation "androidx.paging:paging-runtime:$paging_version"
def room_version = "2.8.4"
implementation("androidx.room:room-runtime:$room_version")
// If this project uses any Kotlin source, use Kotlin Symbol Processing (KSP)
// See KSP Quickstart to add KSP to your build
ksp "androidx.room:room-compiler:$room_version"
// If this project only uses Java source, use the Java annotationProcessor
// No additional plugins are necessary
annotationProcessor("androidx.room:room-compiler:$room_version")
// optional - Kotlin Extensions and Coroutines support for Room
implementation("androidx.room:room-ktx:$room_version")
// optional - Paging 3 Integration
implementation "androidx.room:room-paging:$room_version"
}
Kotlin
import android.content.Context
import android.os.Environment
import android.util.Log
import coil3.EventListener
import coil3.ImageLoader
import coil3.decode.Decoder
import coil3.disk.DiskCache
import coil3.disk.directory
import coil3.fetch.Fetcher
import coil3.imageDecoderEnabled
import coil3.memory.MemoryCache
import coil3.request.CachePolicy
import coil3.request.Disposable
import coil3.request.ImageRequest
import coil3.request.Options
import java.io.File
class MyCoilMgr {
companion object {
const val TAG = "fly/MyCoilMgr"
val INSTANCE by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) { MyCoilMgr() }
}
private var mImageLoader: ImageLoader? = null
private constructor() {
Log.d(TAG, "constructor")
}
fun init(ctx: Context): ImageLoader {
if (mImageLoader != null) {
return mImageLoader!!
}
Log.d(TAG, "初始化ImageLoader")
//初始化加载器。
mImageLoader = ImageLoader.Builder(ctx)
.imageDecoderEnabled(true)
.memoryCachePolicy(CachePolicy.ENABLED)
.memoryCache(initMemoryCache())
.diskCachePolicy(CachePolicy.ENABLED)
.diskCache(initDiskCache())
.eventListener(object : EventListener() {
override fun fetchStart(request: ImageRequest, fetcher: Fetcher, options: Options) {
//Log.d(TAG, "fetchStart ${request.data}")
}
override fun decodeStart(request: ImageRequest, decoder: Decoder, options: Options) {
//Log.d(TAG, "decodeStart ${request.data}")
}
})
.components {
}.build()
return mImageLoader!!
}
private fun initMemoryCache(): MemoryCache {
//内存缓存。
val memoryCache = MemoryCache.Builder()
.maxSizeBytes(1024 * 1024 * 1024 * 2L) //2GB
.build()
return memoryCache
}
private fun initDiskCache(): DiskCache {
//磁盘缓存。
val diskCacheFolder = Environment.getExternalStorageDirectory()
val diskCacheName = "fly_disk_cache"
val cacheFolder = File(diskCacheFolder, diskCacheName)
if (cacheFolder.exists()) {
Log.d(TAG, "${cacheFolder.absolutePath} exists")
} else {
if (cacheFolder.mkdir()) {
Log.d(TAG, "${cacheFolder.absolutePath} create OK")
} else {
Log.e(TAG, "${cacheFolder.absolutePath} create fail")
}
}
val diskCache = DiskCache.Builder()
.maxSizeBytes(1024 * 1024 * 1024 * 2L) //2GB
.directory(cacheFolder)
.build()
Log.d(TAG, "cache folder = ${diskCache.directory.toFile().absolutePath}")
return diskCache
}
fun enqueue(request: ImageRequest): Disposable? {
return mImageLoader?.enqueue(request)
}
fun loader(): ImageLoader {
return mImageLoader!!
}
}
Kotlin
import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
@Database(entities = [MediaEntity::class], version = 1, exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
abstract fun mediaDao(): MediaDao
companion object {
@Volatile
private var INSTANCE: AppDatabase? = null
fun getInstance(context: Context): AppDatabase {
return INSTANCE ?: synchronized(this) {
INSTANCE ?: Room.databaseBuilder(
context.applicationContext,
AppDatabase::class.java,
"media_db"
).build().also { INSTANCE = it }
}
}
}
}
Kotlin
import androidx.paging.PagingSource
import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query
@Dao
interface MediaDao {
@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertAll(list: List<MediaEntity>)
@Query("DELETE FROM media")
suspend fun clearAll()
@Query("SELECT * FROM media ORDER BY dateAdded DESC")
fun pagingSource(): PagingSource<Int, MediaEntity>
@Query("SELECT * FROM media WHERE type = :type ORDER BY dateAdded DESC")
fun pagingSourceByType(type: String): PagingSource<Int, MediaEntity>
}
Kotlin
import androidx.room.Entity
import androidx.room.PrimaryKey
@Entity(tableName = "media")
data class MediaEntity(
@PrimaryKey
val id: Long, // MediaStore._ID
val uri: String, // 文件 uri
val name: String, // 文件名
val path: String?, // 可选，部分系统可能拿不到真实路径
val mimeType: String?,
val size: Long,
val duration: Long = 0L, // 视频时长，图片为0
val dateAdded: Long,
val type: String // IMAGE / VIDEO
)
Kotlin
import android.content.Context
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import androidx.paging.PagingDataAdapter
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.RecyclerView
import coil3.asDrawable
import coil3.request.Disposable
import coil3.request.ImageRequest
import coil3.request.SuccessResult
import coil3.size.Scale
import com.ppdemo.coil.MyCoilMgr
class MediaPagingAdapter(val mCtx: Context) : PagingDataAdapter<MediaEntity, MediaPagingAdapter.MediaViewHolder>(DIFF) {
companion object {
const val TAG = "fly/MediaAdapter"
val DIFF = object : DiffUtil.ItemCallback<MediaEntity>() {
override fun areItemsTheSame(oldItem: MediaEntity, newItem: MediaEntity): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: MediaEntity, newItem: MediaEntity): Boolean {
return oldItem == newItem
}
}
}
private var disposable: Disposable? = null
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MediaViewHolder {
val view = LayoutInflater.from(mCtx).inflate(R.layout.item_media, parent, false)
return MediaViewHolder(view)
}
override fun onBindViewHolder(holder: MediaViewHolder, position: Int) {
holder.imageView.setImageResource(android.R.drawable.gallery_thumb)
val item = getItem(position) ?: return
val req = ImageRequest.Builder(mCtx)
.data(item.path)
.size(PageActivity.IMG_SIZE)
.scale(Scale.FIT)
.listener(object : ImageRequest.Listener {
override fun onSuccess(request: ImageRequest, result: SuccessResult) {
holder.imageView.setImageDrawable(result.image.asDrawable(mCtx.resources))
}
override fun onStart(request: ImageRequest) {
holder.imageView.setImageResource(android.R.drawable.ic_menu_gallery)
}
}).build()
disposable = MyCoilMgr.INSTANCE.enqueue(req)
}
class MediaViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
val imageView: ImageView = itemView.findViewById(R.id.iv)
}
}
Kotlin
import androidx.paging.Pager
import androidx.paging.PagingConfig
import androidx.paging.PagingData
import kotlinx.coroutines.flow.Flow
class MediaRepository(
private val mediaDao: MediaDao
) {
fun getMediaPager(): Flow<PagingData<MediaEntity>> {
return Pager(
config = PagingConfig(
pageSize = 150, // 每页 150 条
initialLoadSize = 150, // 首次也读取 150 条
prefetchDistance = 50, // 提前预取
enablePlaceholders = false
),
pagingSourceFactory = { mediaDao.pagingSource() }
).flow
}
}
Kotlin
enum class MediaType {
IMAGE,
VIDEO
}
Kotlin
import android.app.Application
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.viewModelScope
import androidx.paging.PagingData
import androidx.paging.cachedIn
import kotlinx.coroutines.flow.Flow
class MediaViewModel(application: Application) : AndroidViewModel(application) {
private val db = AppDatabase.getInstance(application)
private val repository = MediaRepository(
db.mediaDao()
)
val mediaPagingFlow: Flow<PagingData<MediaEntity>> =
repository.getMediaPager().cachedIn(viewModelScope)
}
Kotlin
import android.os.Bundle
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.lifecycleScope
import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.RecyclerView
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch
class PageActivity : AppCompatActivity() {
companion object {
const val TAG = "fly/PageActivity"
const val GRID = 6
const val IMG_SIZE = 300
}
private var recyclerView: RecyclerView? = null
private var adapter: MediaPagingAdapter? = null
private var viewModel: MediaViewModel? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_page)
viewModel = ViewModelProvider(this)[MediaViewModel::class.java]
recyclerView = findViewById(R.id.rv)
recyclerView?.layoutManager = GridLayoutManager(this, GRID)
adapter = MediaPagingAdapter(this)
recyclerView?.adapter = adapter
}
override fun onResume() {
super.onResume()
collectPagingData()
}
private fun collectPagingData() {
lifecycleScope.launch(Dispatchers.IO) {
viewModel?.mediaPagingFlow?.collect { pagingData ->
adapter?.submitData(pagingData)
}
}
}
}
Kotlin
import android.app.Application
import com.ppdemo.coil.MyCoilMgr
class MyApp : Application(){
companion object {
const val TAG = "fly/MyApp"
}
override fun onCreate() {
super.onCreate()
MyCoilMgr.INSTANCE.init(this)
}
}相关：https://blog.csdn.net/zhangphil/article/details/160559292