diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/EditActivity.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/EditActivity.kt
index 4ebf3a009..4feaade51 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/EditActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/EditActivity.kt
@@ -72,23 +72,19 @@ class EditActivity : SimpleActivity(), CropImageView.OnCropImageCompleteListener
     override fun onCropImageComplete(view: CropImageView, result: CropImageView.CropResult) {
         if (result.error == null) {
             if (uri.scheme == "file") {
-                SaveAsDialog(this, uri.path, object : SaveAsDialog.OnSaveAsListener {
-                    override fun onSaveAsSuccess(filename: String) {
-                        val parent = File(uri.path).parent
-                        val path = File(parent, filename).absolutePath
-                        saveBitmapToFile(result.bitmap, path)
-                    }
-                })
+                SaveAsDialog(this, uri.path) {
+                    val parent = File(uri.path).parent
+                    val path = File(parent, it).absolutePath
+                    saveBitmapToFile(result.bitmap, path)
+                }
             } else if (uri.scheme == "content") {
                 val newPath = applicationContext.getRealPathFromURI(uri) ?: ""
                 if (!newPath.isEmpty()) {
-                    SaveAsDialog(this, newPath, object : SaveAsDialog.OnSaveAsListener {
-                        override fun onSaveAsSuccess(filename: String) {
-                            val parent = File(uri.path).parent
-                            val path = File(parent, filename).absolutePath
-                            saveBitmapToFile(result.bitmap, path)
-                        }
-                    })
+                    SaveAsDialog(this, newPath) {
+                        val parent = File(uri.path).parent
+                        val path = File(parent, it).absolutePath
+                        saveBitmapToFile(result.bitmap, path)
+                    }
                 } else {
                     toast(R.string.image_editing_failed)
                     finish()
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MainActivity.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MainActivity.kt
index c9cc1aad0..3ed48516d 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MainActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MainActivity.kt
@@ -25,7 +25,7 @@ import kotlinx.android.synthetic.main.activity_main.*
 import java.io.File
 import java.util.*
 
-class MainActivity : SimpleActivity(), GetDirectoriesAsynctask.GetDirectoriesListener, DirectoryAdapter.DirOperationsListener {
+class MainActivity : SimpleActivity(), DirectoryAdapter.DirOperationsListener {
     companion object {
         private val STORAGE_PERMISSION = 1
         private val PICK_MEDIA = 2
@@ -134,16 +134,15 @@ class MainActivity : SimpleActivity(), GetDirectoriesAsynctask.GetDirectoriesLis
             return
 
         mIsGettingDirs = true
-        GetDirectoriesAsynctask(applicationContext, mIsPickVideoIntent || mIsGetVideoContentIntent, mIsPickImageIntent || mIsGetImageContentIntent,
-                mToBeDeleted, this).execute()
+        GetDirectoriesAsynctask(applicationContext, mIsPickVideoIntent || mIsGetVideoContentIntent, mIsPickImageIntent || mIsGetImageContentIntent, mToBeDeleted) {
+            gotDirectories(it)
+        }.execute()
     }
 
     private fun showSortingDialog() {
-        ChangeSortingDialog(this, true, object : ChangeSortingDialog.OnChangeSortingListener {
-            override fun sortingChanged() {
-                getDirectories()
-            }
-        })
+        ChangeSortingDialog(this, true) {
+            getDirectories()
+        }
     }
 
     override fun prepareForDeleting(paths: ArrayList<String>) {
@@ -285,7 +284,7 @@ class MainActivity : SimpleActivity(), GetDirectoriesAsynctask.GetDirectoriesLis
         }
     }
 
-    override fun gotDirectories(dirs: ArrayList<Directory>) {
+    fun gotDirectories(dirs: ArrayList<Directory>) {
         directories_holder.isRefreshing = false
         mIsGettingDirs = false
         if (dirs.toString() == mDirs.toString()) {
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MediaActivity.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MediaActivity.kt
index 3c96af1d7..412c05aec 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MediaActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/MediaActivity.kt
@@ -128,11 +128,9 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
     }
 
     private fun showSortingDialog() {
-        ChangeSortingDialog(this, false, object : ChangeSortingDialog.OnChangeSortingListener {
-            override fun sortingChanged() {
-                getMedia()
-            }
-        })
+        ChangeSortingDialog(this, false) {
+            getMedia()
+        }
     }
 
     private fun hideDirectory() {
@@ -161,18 +159,9 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
             return
 
         mIsGettingMedia = true
-        GetMediaAsynctask(applicationContext, mPath, mIsGetVideoIntent, mIsGetImageIntent, mToBeDeleted, object : GetMediaAsynctask.GetMediaListener {
-            override fun gotMedia(media: ArrayList<Medium>) {
-                mIsGettingMedia = false
-                media_holder.isRefreshing = false
-                if (media.toString() == mMedia.toString()) {
-                    return
-                }
-
-                mMedia = media
-                initializeGallery()
-            }
-        }).execute()
+        GetMediaAsynctask(applicationContext, mPath, mIsGetVideoIntent, mIsGetImageIntent, mToBeDeleted) {
+            gotMedia(it)
+        }.execute()
     }
 
     private fun isDirEmpty(): Boolean {
@@ -304,6 +293,17 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         }
     }
 
+    fun gotMedia(media: ArrayList<Medium>) {
+        mIsGettingMedia = false
+        media_holder.isRefreshing = false
+        if (media.toString() == mMedia.toString()) {
+            return
+        }
+
+        mMedia = media
+        initializeGallery()
+    }
+
     fun checkDelete() {
         if (mSnackbar?.isShown == true) {
             deleteFiles()
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt
index 908a2ef5c..65f536492 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/activities/ViewPagerActivity.kt
@@ -315,12 +315,10 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
     }
 
     private fun editMedium() {
-        RenameFileDialog(this, getCurrentFile(), object : RenameFileDialog.OnRenameFileListener {
-            override fun onRenameFileSuccess(newFile: File) {
-                mMedia!![view_pager.currentItem].path = newFile.absolutePath
-                updateActionbarTitle()
-            }
-        })
+        RenameFileDialog(this, getCurrentFile()) {
+            mMedia!![view_pager.currentItem].path = it.absolutePath
+            updateActionbarTitle()
+        }
     }
 
     private fun reloadViewPager() {
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/adapters/DirectoryAdapter.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/adapters/DirectoryAdapter.kt
index bb4a71316..a1d6ceb9a 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/adapters/DirectoryAdapter.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/adapters/DirectoryAdapter.kt
@@ -140,17 +140,15 @@ class DirectoryAdapter(val activity: SimpleActivity, val dirs: MutableList<Direc
             return
         }
 
-        RenameDirectoryDialog(activity, dir, object : RenameDirectoryDialog.OnRenameDirListener {
-            override fun onRenameDirSuccess(changedPaths: ArrayList<String>) {
-                activity.scanPaths(changedPaths) {
-                    activity.runOnUiThread {
-                        actMode?.finish()
-                        listener?.refreshItems()
-                        activity.toast(R.string.rename_folder_ok)
-                    }
+        RenameDirectoryDialog(activity, dir) {
+            activity.scanPaths(it) {
+                activity.runOnUiThread {
+                    actMode?.finish()
+                    listener?.refreshItems()
+                    activity.toast(R.string.rename_folder_ok)
                 }
             }
-        })
+        }
     }
 
     private fun hideDirs() {
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetDirectoriesAsynctask.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetDirectoriesAsynctask.kt
index a22c56687..abd01ae59 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetDirectoriesAsynctask.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetDirectoriesAsynctask.kt
@@ -12,18 +12,15 @@ import com.simplemobiletools.gallery.SORT_DESCENDING
 import com.simplemobiletools.gallery.extensions.getHumanizedFilename
 import com.simplemobiletools.gallery.models.Directory
 import java.io.File
-import java.lang.ref.WeakReference
 import java.util.*
 
 class GetDirectoriesAsynctask(val context: Context, val isPickVideo: Boolean, val isPickImage: Boolean,
-                              val mToBeDeleted: List<String>, val listener: GetDirectoriesListener) : AsyncTask<Void, Void, ArrayList<Directory>>() {
+                              val mToBeDeleted: List<String>, val callback: (dirs: ArrayList<Directory>) -> Unit) : AsyncTask<Void, Void, ArrayList<Directory>>() {
     lateinit var mConfig: Config
-    lateinit var mListener: WeakReference<GetDirectoriesListener>
 
     override fun onPreExecute() {
         super.onPreExecute()
         mConfig = Config.newInstance(context)
-        mListener = WeakReference(listener)
     }
 
     override fun doInBackground(vararg params: Void): ArrayList<Directory> {
@@ -91,8 +88,7 @@ class GetDirectoriesAsynctask(val context: Context, val isPickVideo: Boolean, va
 
     override fun onPostExecute(dirs: ArrayList<Directory>) {
         super.onPostExecute(dirs)
-        val listener = mListener.get()
-        listener?.gotDirectories(dirs)
+        callback.invoke(dirs)
     }
 
     // sort the files at querying too, just to get the correct thumbnail
@@ -135,8 +131,4 @@ class GetDirectoriesAsynctask(val context: Context, val isPickVideo: Boolean, va
 
         dirs.removeAll(ignoreDirs)
     }
-
-    interface GetDirectoriesListener {
-        fun gotDirectories(dirs: ArrayList<Directory>)
-    }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetMediaAsynctask.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetMediaAsynctask.kt
index 01e9f6336..31585ead5 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetMediaAsynctask.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/asynctasks/GetMediaAsynctask.kt
@@ -8,19 +8,16 @@ import com.simplemobiletools.filepicker.extensions.scanFiles
 import com.simplemobiletools.gallery.Config
 import com.simplemobiletools.gallery.models.Medium
 import java.io.File
-import java.lang.ref.WeakReference
 import java.util.*
 import java.util.regex.Pattern
 
 class GetMediaAsynctask(val context: Context, val mPath: String, val isPickVideo: Boolean, val isPickImage: Boolean,
-                        val mToBeDeleted: List<String>, val listener: GetMediaListener) : AsyncTask<Void, Void, ArrayList<Medium>>() {
+                        val mToBeDeleted: List<String>, val callback: (media: ArrayList<Medium>) -> Unit) : AsyncTask<Void, Void, ArrayList<Medium>>() {
     lateinit var mConfig: Config
-    lateinit var mListener: WeakReference<GetMediaListener>
 
     override fun onPreExecute() {
         super.onPreExecute()
         mConfig = Config.newInstance(context)
-        mListener = WeakReference(listener)
     }
 
     override fun doInBackground(vararg params: Void): ArrayList<Medium> {
@@ -76,11 +73,6 @@ class GetMediaAsynctask(val context: Context, val mPath: String, val isPickVideo
 
     override fun onPostExecute(media: ArrayList<Medium>) {
         super.onPostExecute(media)
-        val listener = mListener.get()
-        listener?.gotMedia(media)
-    }
-
-    interface GetMediaListener {
-        fun gotMedia(media: ArrayList<Medium>)
+        callback.invoke(media)
     }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/ChangeSortingDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/ChangeSortingDialog.kt
index f71261cb9..c5b939178 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/ChangeSortingDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/ChangeSortingDialog.kt
@@ -8,7 +8,7 @@ import android.view.View
 import com.simplemobiletools.gallery.*
 import kotlinx.android.synthetic.main.dialog_change_sorting.view.*
 
-class ChangeSortingDialog(val activity: Activity, val isDirectorySorting: Boolean, val listener: OnChangeSortingListener) : DialogInterface.OnClickListener {
+class ChangeSortingDialog(val activity: Activity, val isDirectorySorting: Boolean, val callback: () -> Unit) : DialogInterface.OnClickListener {
     companion object {
         private var currSorting = 0
 
@@ -76,10 +76,6 @@ class ChangeSortingDialog(val activity: Activity, val isDirectorySorting: Boolea
                 config.sorting = sorting
             }
         }
-        listener.sortingChanged()
-    }
-
-    interface OnChangeSortingListener {
-        fun sortingChanged()
+        callback.invoke()
     }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/CopyDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/CopyDialog.kt
index daae39ba4..cba853a19 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/CopyDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/CopyDialog.kt
@@ -26,12 +26,10 @@ class CopyDialog(val activity: SimpleActivity, val files: ArrayList<File>, val c
         view.source.text = activity.humanizePath(sourcePath)
 
         view.destination.setOnClickListener {
-            PickAlbumDialog(activity, object : PickAlbumDialog.OnPickAlbumListener {
-                override fun onSuccess(path: String) {
-                    destinationPath = path
-                    view.destination.text = activity.humanizePath(path)
-                }
-            })
+            PickAlbumDialog(activity) {
+                destinationPath = it
+                view.destination.text = activity.humanizePath(it)
+            }
         }
 
         AlertDialog.Builder(activity)
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/PickAlbumDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/PickAlbumDialog.kt
index da25e292f..1272ea837 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/PickAlbumDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/PickAlbumDialog.kt
@@ -7,11 +7,10 @@ import com.simplemobiletools.gallery.R
 import com.simplemobiletools.gallery.activities.SimpleActivity
 import com.simplemobiletools.gallery.adapters.DirectoryAdapter
 import com.simplemobiletools.gallery.asynctasks.GetDirectoriesAsynctask
-import com.simplemobiletools.gallery.models.Directory
 import kotlinx.android.synthetic.main.dialog_album_picker.view.*
 import java.util.*
 
-class PickAlbumDialog(val activity: SimpleActivity, val listener: OnPickAlbumListener) : GetDirectoriesAsynctask.GetDirectoriesListener {
+class PickAlbumDialog(val activity: SimpleActivity, val callback: (path: String) -> Unit) {
     var dialog: AlertDialog
     var directoriesGrid: RecyclerView
 
@@ -27,18 +26,12 @@ class PickAlbumDialog(val activity: SimpleActivity, val listener: OnPickAlbumLis
                 .create()
 
         dialog.show()
-        GetDirectoriesAsynctask(activity, false, false, ArrayList<String>(), this).execute()
-    }
-
-    override fun gotDirectories(dirs: ArrayList<Directory>) {
-        val adapter = DirectoryAdapter(activity, dirs, null) {
-            listener.onSuccess(it.path)
-            dialog.dismiss()
-        }
-        directoriesGrid.adapter = adapter
-    }
-
-    interface OnPickAlbumListener {
-        fun onSuccess(path: String)
+        GetDirectoriesAsynctask(activity, false, false, ArrayList<String>()) {
+            val adapter = DirectoryAdapter(activity, it, null) {
+                callback.invoke(it.path)
+                dialog.dismiss()
+            }
+            directoriesGrid.adapter = adapter
+        }.execute()
     }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameDirectoryDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameDirectoryDialog.kt
index 03b0d3209..101b9fc55 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameDirectoryDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameDirectoryDialog.kt
@@ -11,7 +11,7 @@ import kotlinx.android.synthetic.main.rename_directory.view.*
 import java.io.File
 import java.util.*
 
-class RenameDirectoryDialog(val activity: SimpleActivity, val dir: File, val listener: OnRenameDirListener) {
+class RenameDirectoryDialog(val activity: SimpleActivity, val dir: File, val callback: (changedPaths: ArrayList<String>) -> Unit) {
     init {
         val view = LayoutInflater.from(activity).inflate(R.layout.rename_directory, null)
 
@@ -72,10 +72,6 @@ class RenameDirectoryDialog(val activity: SimpleActivity, val dir: File, val lis
         files.mapTo(updatedFiles) { it.absolutePath }
 
         updatedFiles.add(newDir.absolutePath)
-        listener.onRenameDirSuccess(updatedFiles)
-    }
-
-    interface OnRenameDirListener {
-        fun onRenameDirSuccess(changedPaths: ArrayList<String>)
+        callback.invoke(updatedFiles)
     }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameFileDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameFileDialog.kt
index b135e15d9..ebb7470f4 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameFileDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/RenameFileDialog.kt
@@ -10,7 +10,7 @@ import com.simplemobiletools.gallery.activities.SimpleActivity
 import kotlinx.android.synthetic.main.rename_file.view.*
 import java.io.File
 
-class RenameFileDialog(val activity: SimpleActivity, val file: File, val listener: OnRenameFileListener) {
+class RenameFileDialog(val activity: SimpleActivity, val file: File, val callback: (newFile: File) -> Unit) {
 
     init {
         val view = LayoutInflater.from(activity).inflate(R.layout.rename_file, null)
@@ -73,10 +73,6 @@ class RenameFileDialog(val activity: SimpleActivity, val file: File, val listene
     private fun sendSuccess(currFile: File, newFile: File) {
         val changedFiles = arrayListOf(currFile, newFile)
         activity.scanFiles(changedFiles) {}
-        listener.onRenameFileSuccess(newFile)
-    }
-
-    interface OnRenameFileListener {
-        fun onRenameFileSuccess(newFile: File)
+        callback.invoke(newFile)
     }
 }
diff --git a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/SaveAsDialog.kt b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/SaveAsDialog.kt
index 8aae9029b..627ae71f6 100644
--- a/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/SaveAsDialog.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/gallery/dialogs/SaveAsDialog.kt
@@ -11,7 +11,7 @@ import com.simplemobiletools.filepicker.extensions.value
 import com.simplemobiletools.gallery.R
 import kotlinx.android.synthetic.main.rename_file.view.*
 
-class SaveAsDialog(val activity: Activity, val path: String, val listener: OnSaveAsListener) {
+class SaveAsDialog(val activity: Activity, val path: String, val callback: (filename: String) -> Unit) {
 
     init {
         val view = LayoutInflater.from(activity).inflate(R.layout.dialog_save_as, null)
@@ -38,13 +38,9 @@ class SaveAsDialog(val activity: Activity, val path: String, val listener: OnSav
                     return@setOnClickListener
                 }
 
-                listener.onSaveAsSuccess(filename)
+                callback.invoke(filename)
                 dismiss()
             })
         }
     }
-
-    interface OnSaveAsListener {
-        fun onSaveAsSuccess(filename: String)
-    }
 }