lets use Room for caching directories

app/build.gradle

@@ -1,6 +1,7 @@
 apply plugin: 'com.android.application'
 apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-android-extensions'
+apply plugin: 'kotlin-kapt'
 
 android {
     compileSdkVersion 27
@@ -53,6 +54,10 @@ dependencies {
     implementation 'pl.droidsonroids.gif:android-gif-drawable:1.2.12'
     implementation 'com.github.chrisbanes:PhotoView:2.1.3'
 
+    kapt "android.arch.persistence.room:compiler:1.0.0"
+    implementation "android.arch.persistence.room:runtime:1.0.0"
+    annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
+
     //implementation 'com.davemorrissey.labs:subsampling-scale-image-view:3.9.0'
     implementation 'com.github.tibbi:subsampling-scale-image-view:v3.10.0-fork'
 

app/src/main/kotlin/com/simplemobiletools/gallery/activities/MainActivity.kt

@@ -29,6 +29,7 @@ import com.simplemobiletools.gallery.BuildConfig
 import com.simplemobiletools.gallery.R
 import com.simplemobiletools.gallery.adapters.DirectoryAdapter
 import com.simplemobiletools.gallery.asynctasks.GetDirectoriesAsynctask
+import com.simplemobiletools.gallery.databases.DirectoryDataBase
 import com.simplemobiletools.gallery.dialogs.ChangeSortingDialog
 import com.simplemobiletools.gallery.dialogs.FilterMediaDialog
 import com.simplemobiletools.gallery.extensions.*
@@ -62,6 +63,7 @@ class MainActivity : SimpleActivity(), DirectoryAdapter.DirOperationsListener {
     private var mTempShowHiddenHandler = Handler()
     private var mCurrAsyncTask: GetDirectoriesAsynctask? = null
     private var mZoomListener: MyRecyclerView.MyZoomListener? = null
+    private var mDirsDB: DirectoryDataBase? = null
 
     private var mStoredAnimateGifs = true
     private var mStoredCropThumbnails = true
@@ -89,6 +91,7 @@ class MainActivity : SimpleActivity(), DirectoryAdapter.DirOperationsListener {
         removeTempFolder()
         directories_refresh_layout.setOnRefreshListener { getDirectories() }
         mDirs = ArrayList()
+        mDirsDB = DirectoryDataBase.getInstance(applicationContext)
         storeStateVariables()
         checkWhatsNewDialog()
 
@@ -551,11 +554,14 @@ class MainActivity : SimpleActivity(), DirectoryAdapter.DirOperationsListener {
     }
 
     private fun gotDirectories(newDirs: ArrayList<Directory>, isFromCache: Boolean) {
-        /*if (!isFromCache) {
+        if (!isFromCache) {
             Thread {
-                checkFolderContentChange(newDirs)
+                //checkFolderContentChange(newDirs)
+                newDirs.forEach {
+                    mDirsDB!!.DirectoryDao().insert(it)
+                }
             }.start()
-        }*/
+        }
 
         val dirs = getSortedDirectories(newDirs)
         directories_refresh_layout.isRefreshing = false

app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetDirectoriesAsynctask.kt

@@ -38,7 +38,12 @@ class GetDirectoriesAsynctask(val context: Context, val isPickVideo: Boolean, va
 
             val firstItem = curMedia.first()
             val lastItem = curMedia.last()
-            val parentDir = if (hasOTG && firstItem.path.startsWith(OTG_PATH)) firstItem.path.getParentPath() else File(firstItem.path).parent ?: continue
+            val parentDir = if (hasOTG && firstItem.path.startsWith(OTG_PATH)) {
+                firstItem.path.getParentPath()
+            } else {
+                File(firstItem.path).parent
+            } ?: continue
+
             var thumbnail = curMedia.firstOrNull { context.getDoesFilePathExist(it.path) }?.path ?: ""
             if (thumbnail.startsWith(OTG_PATH)) {
                 thumbnail = thumbnail.getOTGPublicPath(context)
@@ -54,7 +59,7 @@ class GetDirectoriesAsynctask(val context: Context, val isPickVideo: Boolean, va
             val lastModified = if (config.directorySorting and SORT_DESCENDING > 0) Math.max(firstItem.modified, lastItem.modified) else Math.min(firstItem.modified, lastItem.modified)
             val dateTaken = if (config.directorySorting and SORT_DESCENDING > 0) Math.max(firstItem.taken, lastItem.taken) else Math.min(firstItem.taken, lastItem.taken)
             val size = curMedia.sumByLong { it.size }
-            val directory = Directory(parentDir, thumbnail, dirName, curMedia.size, lastModified, dateTaken, size, context.isPathOnSD(parentDir))
+            val directory = Directory(null, parentDir, thumbnail, dirName, curMedia.size, lastModified, dateTaken, size, context.isPathOnSD(parentDir))
             directories.add(directory)
         }
 

app/src/main/kotlin/com/simplemobiletools/gallery/databases/DirectoryDataBase.kt

@@ -0,0 +1,31 @@
+package com.simplemobiletools.gallery.databases
+
+import android.arch.persistence.room.Database
+import android.arch.persistence.room.Room
+import android.arch.persistence.room.RoomDatabase
+import android.content.Context
+import com.simplemobiletools.gallery.interfaces.DirectoryDao
+import com.simplemobiletools.gallery.models.Directory
+
+@Database(entities = [(Directory::class)], version = 1)
+abstract class DirectoryDataBase : RoomDatabase() {
+
+    abstract fun DirectoryDao(): DirectoryDao
+
+    companion object {
+        private var INSTANCE: DirectoryDataBase? = null
+
+        fun getInstance(context: Context): DirectoryDataBase {
+            if (INSTANCE == null) {
+                synchronized(DirectoryDataBase::class) {
+                    INSTANCE = Room.databaseBuilder(context.applicationContext, DirectoryDataBase::class.java, "directories.db").build()
+                }
+            }
+            return INSTANCE!!
+        }
+
+        fun destroyInstance() {
+            INSTANCE = null
+        }
+    }
+}

app/src/main/kotlin/com/simplemobiletools/gallery/extensions/Activity.kt

@@ -211,7 +211,7 @@ fun BaseSimpleActivity.addTempFolderIfNeeded(dirs: ArrayList<Directory>): ArrayL
     val directories = ArrayList<Directory>()
     val tempFolderPath = config.tempFolderPath
     if (tempFolderPath.isNotEmpty()) {
-        val newFolder = Directory(tempFolderPath, "", tempFolderPath.getFilenameFromPath(), 0, 0, 0, 0L, isPathOnSD(tempFolderPath))
+        val newFolder = Directory(null, tempFolderPath, "", tempFolderPath.getFilenameFromPath(), 0, 0, 0, 0L, isPathOnSD(tempFolderPath))
         directories.add(newFolder)
     }
     directories.addAll(dirs)

app/src/main/kotlin/com/simplemobiletools/gallery/interfaces/DirectoryDao.kt

@@ -0,0 +1,16 @@
+package com.simplemobiletools.gallery.interfaces
+
+import android.arch.persistence.room.Dao
+import android.arch.persistence.room.Insert
+import android.arch.persistence.room.OnConflictStrategy.REPLACE
+import android.arch.persistence.room.Query
+import com.simplemobiletools.gallery.models.Directory
+
+@Dao
+interface DirectoryDao {
+    @Query("SELECT * from directories")
+    fun getAll(): List<Directory>
+
+    @Insert(onConflict = REPLACE)
+    fun insert(directory: Directory)
+}

app/src/main/kotlin/com/simplemobiletools/gallery/models/Directory.kt

@@ -1,14 +1,28 @@
 package com.simplemobiletools.gallery.models
 
+import android.arch.persistence.room.ColumnInfo
+import android.arch.persistence.room.Entity
+import android.arch.persistence.room.Index
+import android.arch.persistence.room.PrimaryKey
 import com.simplemobiletools.commons.extensions.formatDate
 import com.simplemobiletools.commons.extensions.formatSize
 import com.simplemobiletools.commons.helpers.*
 import java.io.Serializable
 
-data class Directory(var path: String, var tmb: String, var name: String, var mediaCnt: Int, val modified: Long, val taken: Long,
+@Entity(tableName = "directories", indices = [Index(value = "path", unique = true)])
-                     val size: Long, val isOnSDCard: Boolean) : Serializable, Comparable<Directory> {
+data class Directory(
+        @PrimaryKey(autoGenerate = true) var id: Long?,
+        @ColumnInfo(name = "path") var path: String,
+        @ColumnInfo(name = "thumbnail") var tmb: String,
+        @ColumnInfo(name = "filename") var name: String,
+        @ColumnInfo(name = "media_count") var mediaCnt: Int,
+        @ColumnInfo(name = "last_modified") val modified: Long,
+        @ColumnInfo(name = "date_taken") val taken: Long,
+        @ColumnInfo(name = "size") val size: Long,
+        @ColumnInfo(name = "is_on_sd_card") val isOnSDCard: Boolean) : Serializable, Comparable<Directory> {
+
     companion object {
-        private val serialVersionUID = -6553345863555455L
+        private const val serialVersionUID = -6553345863555455L
         var sorting: Int = 0
     }
 

app/src/main/kotlin/com/simplemobiletools/gallery/models/Medium.kt

@@ -2,7 +2,6 @@ package com.simplemobiletools.gallery.models
 
 import com.simplemobiletools.commons.extensions.formatDate
 import com.simplemobiletools.commons.extensions.formatSize
-import com.simplemobiletools.commons.extensions.getMimeType
 import com.simplemobiletools.commons.extensions.isDng
 import com.simplemobiletools.commons.helpers.*
 import com.simplemobiletools.gallery.helpers.TYPE_GIF
@@ -12,7 +11,7 @@ import java.io.Serializable
 
 data class Medium(var name: String, var path: String, val modified: Long, val taken: Long, val size: Long, val type: Int) : Serializable, Comparable<Medium> {
     companion object {
-        private val serialVersionUID = -6553149366975455L
+        private const val serialVersionUID = -6553149366975455L
         var sorting: Int = 0
     }
 
@@ -24,8 +23,6 @@ data class Medium(var name: String, var path: String, val modified: Long, val ta
 
     fun isDng() = path.isDng()
 
-    fun getMimeType() = path.getMimeType()
-
     override fun compareTo(other: Medium): Int {
         var result: Int
         when {