mark the currently selected filter with a white stroke

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

@@ -286,7 +286,7 @@ class EditActivity : SimpleActivity(), CropImageView.OnCropImageCompleteListener
                     }
 
                     val filterItems = filterThumbnailsManager.processThumbs()
-                    val adapter = FiltersAdapter(filterItems) {
+                    val adapter = FiltersAdapter(applicationContext, filterItems) {
                         val newBitmap = Bitmap.createBitmap(shownBitmap)
                         default_image_view.setImageBitmap(it.filter.processFilter(newBitmap))
                     }

app/src/main/kotlin/com/simplemobiletools/gallery/adapters/FiltersAdapter.kt

@@ -1,35 +1,57 @@
 package com.simplemobiletools.gallery.adapters
 
+import android.content.Context
+import android.graphics.drawable.Drawable
 import android.support.v7.widget.RecyclerView
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import com.simplemobiletools.gallery.R
+import com.simplemobiletools.gallery.interfaces.FilterAdapterListener
 import com.simplemobiletools.gallery.models.FilterItem
 import kotlinx.android.synthetic.main.editor_filter_item.view.*
 import java.util.*
 
-class FiltersAdapter(val filterItems: ArrayList<FilterItem>, val itemClick: (FilterItem) -> Unit) : RecyclerView.Adapter<FiltersAdapter.ViewHolder>() {
+class FiltersAdapter(val context: Context, val filterItems: ArrayList<FilterItem>, val itemClick: (FilterItem) -> Unit) : RecyclerView.Adapter<FiltersAdapter.ViewHolder>(),
+        FilterAdapterListener {
+
+    private var currentSelection = filterItems.first()
+    private var strokeBackground = context.resources.getDrawable(R.drawable.stroke_background)
 
     override fun onBindViewHolder(holder: ViewHolder, position: Int) {
-        holder.bindView(filterItems[position], itemClick)
+        holder.bindView(filterItems[position], strokeBackground)
     }
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
         val view = LayoutInflater.from(parent.context).inflate(R.layout.editor_filter_item, parent, false)
-        return ViewHolder(view)
+        return ViewHolder(view, this)
     }
 
     override fun getItemCount() = filterItems.size
 
-    class ViewHolder(view: View) : RecyclerView.ViewHolder(view) {
-        fun bindView(filterItem: FilterItem, itemClick: (FilterItem) -> Unit): View {
+    override fun getCurrentFilter() = currentSelection
+
+    override fun setCurrentFilter(filterItem: FilterItem) {
+        if (currentSelection != filterItem) {
+            currentSelection = filterItem
+            notifyDataSetChanged()
+            itemClick.invoke(filterItem)
+        }
+    }
+
+    class ViewHolder(view: View, val filterAdapterListener: FilterAdapterListener) : RecyclerView.ViewHolder(view) {
+        fun bindView(filterItem: FilterItem, strokeBackground: Drawable): View {
             itemView.apply {
                 editor_filter_item_label.text = filterItem.filter.name
                 editor_filter_item_thumbnail.setImageBitmap(filterItem.bitmap)
+                editor_filter_item_thumbnail.background = if (filterAdapterListener.getCurrentFilter() == filterItem) {
+                    strokeBackground
+                } else {
+                    null
+                }
 
                 setOnClickListener {
-                    itemClick.invoke(filterItem)
+                    filterAdapterListener.setCurrentFilter(filterItem)
                 }
             }
             return itemView

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

@@ -0,0 +1,9 @@
+package com.simplemobiletools.gallery.interfaces
+
+import com.simplemobiletools.gallery.models.FilterItem
+
+interface FilterAdapterListener {
+    fun getCurrentFilter(): FilterItem
+
+    fun setCurrentFilter(filterItem: FilterItem)
+}

app/src/main/res/drawable/stroke_background.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<selector xmlns:android="http://schemas.android.com/apk/res/android">
+    <item>
+        <shape android:shape="rectangle">
+            <stroke android:width="1dp" android:color="#FFFFFFFF"/>
+        </shape>
+    </item>
+</selector>

app/src/main/res/layout/editor_filter_item.xml

@@ -4,16 +4,15 @@
     xmlns:tools="http://schemas.android.com/tools"
     android:id="@+id/editor_filter_item_holder"
     android:layout_width="wrap_content"
-    android:layout_height="wrap_content"
-    android:paddingLeft="@dimen/tiny_margin"
-    android:paddingRight="@dimen/tiny_margin"
-    android:paddingTop="@dimen/tiny_margin">
+    android:layout_height="wrap_content">
 
     <ImageView
         android:id="@+id/editor_filter_item_thumbnail"
         android:layout_width="@dimen/bottom_filters_thumbnail_height"
         android:layout_height="@dimen/bottom_filters_thumbnail_height"
-        android:layout_above="@+id/editor_filter_item_label"/>
+        android:layout_above="@+id/editor_filter_item_label"
+        android:background="@drawable/stroke_background"
+        android:padding="1dp"/>
 
     <TextView
         android:id="@+id/editor_filter_item_label"