add an initial fast scrollbar to thumbnail view

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

@@ -56,7 +56,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
             mIsGetAnyIntent = getBooleanExtra(GET_ANY_INTENT, false)
         }
 
-        media_holder.setOnRefreshListener({ getMedia() })
+        media_refresh_layout.setOnRefreshListener({ getMedia() })
         mPath = intent.getStringExtra(DIRECTORY)
         mStoredAnimateGifs = config.animateGifs
         mShowAll = config.showAll
@@ -76,7 +76,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         super.onPause()
         mCurrAsyncTask?.shouldStop = true
         mIsGettingMedia = false
-        media_holder.isRefreshing = false
+        media_refresh_layout.isRefreshing = false
         mStoredAnimateGifs = config.animateGifs
     }
 
@@ -105,6 +105,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         } else {
             media_grid.adapter = adapter
         }
+        media_fastscroller.setViews(media_grid, media_refresh_layout)
     }
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
@@ -214,7 +215,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
         val token = object : TypeToken<List<Medium>>() {}.type
         val media = Gson().fromJson<ArrayList<Medium>>(config.loadFolderMedia(mPath), token) ?: ArrayList<Medium>(1)
         if (media.size == 0) {
-            media_holder.isRefreshing = true
+            media_refresh_layout.isRefreshing = true
         } else {
             if (!mLoadedInitialPhotos)
                 gotMedia(media)
@@ -339,7 +340,7 @@ class MediaActivity : SimpleActivity(), MediaAdapter.MediaOperationsListener {
 
     fun gotMedia(media: ArrayList<Medium>) {
         mIsGettingMedia = false
-        media_holder.isRefreshing = false
+        media_refresh_layout.isRefreshing = false
 
         if (media.hashCode() == mMedia.hashCode())
             return

app/src/main/kotlin/com/simplemobiletools/gallery/views/FastScroller.kt

@@ -0,0 +1,121 @@
+package com.simplemobiletools.gallery.views
+
+import android.content.Context
+import android.support.v4.widget.SwipeRefreshLayout
+import android.support.v7.widget.GridLayoutManager
+import android.support.v7.widget.RecyclerView
+import android.util.AttributeSet
+import android.view.LayoutInflater
+import android.view.MotionEvent
+import android.view.View
+import android.widget.LinearLayout
+import com.simplemobiletools.gallery.R
+import kotlinx.android.synthetic.main.fastscroller.view.*
+
+// based on https://blog.stylingandroid.com/recyclerview-fastscroll-part-1
+class FastScroller : LinearLayout {
+    private val handle: View
+    private var currHeight = 0
+
+    private val HANDLE_HIDE_DELAY = 1000L
+    private var recyclerView: RecyclerView? = null
+    private var swipeRefreshLayout: SwipeRefreshLayout? = null
+
+    constructor(context: Context) : super(context)
+
+    constructor(context: Context, attrs: AttributeSet) : super(context, attrs)
+
+    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle)
+
+    fun setViews(recyclerView: RecyclerView, swipeRefreshLayout: SwipeRefreshLayout) {
+        this.recyclerView = recyclerView
+        this.swipeRefreshLayout = swipeRefreshLayout
+
+        recyclerView.setOnScrollListener(object : RecyclerView.OnScrollListener() {
+            override fun onScrolled(rv: RecyclerView, dx: Int, dy: Int) {
+                updateHandlePosition()
+            }
+
+            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
+                super.onScrollStateChanged(recyclerView, newState)
+                if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {
+                    showHandle()
+                } else if (newState == RecyclerView.SCROLL_STATE_IDLE) {
+                    hideHandle()
+                }
+            }
+        })
+    }
+
+    override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
+        super.onSizeChanged(w, h, oldw, oldh)
+        currHeight = h
+        updateHandlePosition()
+    }
+
+    private fun updateHandlePosition() {
+        if (handle.isSelected)
+            return
+
+        val verticalScrollOffset = recyclerView!!.computeVerticalScrollOffset()
+        val verticalScrollRange = recyclerView!!.computeVerticalScrollRange()
+        val proportion = verticalScrollOffset.toFloat() / (verticalScrollRange.toFloat() - currHeight)
+        setPosition(currHeight * proportion)
+    }
+
+    override fun onTouchEvent(event: MotionEvent): Boolean {
+        return when (event.action) {
+            MotionEvent.ACTION_DOWN -> {
+                showHandle()
+                handle.isSelected = true
+                swipeRefreshLayout?.isEnabled = false
+                true
+            }
+            MotionEvent.ACTION_MOVE -> {
+                setPosition(event.y)
+                setRecyclerViewPosition(event.y)
+                true
+            }
+            MotionEvent.ACTION_UP, MotionEvent.ACTION_CANCEL -> {
+                hideHandle()
+                handle.isSelected = false
+                swipeRefreshLayout?.isEnabled = true
+                true
+            }
+            else -> super.onTouchEvent(event)
+        }
+    }
+
+    private fun setRecyclerViewPosition(y: Float) {
+        if (recyclerView != null) {
+            val itemCount = recyclerView!!.adapter.itemCount
+            val proportion = y / currHeight
+            val targetPos = getValueInRange(0f, (itemCount - 1).toFloat(), proportion * itemCount).toInt()
+            (recyclerView!!.layoutManager as GridLayoutManager).scrollToPositionWithOffset(targetPos, 0)
+        }
+    }
+
+    init {
+        orientation = LinearLayout.HORIZONTAL
+        clipChildren = false
+        val inflater = LayoutInflater.from(context)
+        inflater.inflate(R.layout.fastscroller, this)
+        handle = fastscroller_handle
+    }
+
+    private fun showHandle() {
+        handle.animate().alpha(1f).startDelay = 0L
+    }
+
+    private fun hideHandle() {
+        handle.animate().alpha(0f).startDelay = HANDLE_HIDE_DELAY
+    }
+
+    private fun setPosition(y: Float) {
+        val position = y / currHeight
+        val handleHeight = handle.height
+        handle.y = getValueInRange(0f, (currHeight - handleHeight).toFloat(), (currHeight - handleHeight) * position)
+    }
+
+    private fun getValueInRange(min: Float, max: Float, value: Float) = Math.min(Math.max(min, value), max)
+}

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

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shape="rectangle">
+
+    <corners android:radius="@dimen/small_margin"/>
+
+    <solid android:color="@color/color_primary"/>
+
+    <size
+        android:width="@dimen/fastscroll_width"
+        android:height="@dimen/fastscroll_height"/>
+</shape>

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

@@ -2,16 +2,31 @@
 <android.support.v4.widget.SwipeRefreshLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
-    android:id="@+id/media_holder"
+    android:id="@+id/media_refresh_layout"
     android:layout_width="match_parent"
     android:layout_height="wrap_content">
 
-    <com.simplemobiletools.gallery.views.MyScalableRecyclerView
-        android:id="@+id/media_grid"
+    <RelativeLayout
+        android:id="@+id/media_holder"
         android:layout_width="match_parent"
-        android:layout_height="match_parent"
-        android:scrollbars="vertical"
-        app:layoutManager="android.support.v7.widget.GridLayoutManager"
-        app:spanCount="@integer/media_columns"/>
+        android:layout_height="wrap_content">
 
+        <com.simplemobiletools.gallery.views.MyScalableRecyclerView
+            android:id="@+id/media_grid"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:scrollbars="none"
+            app:layoutManager="android.support.v7.widget.GridLayoutManager"
+            app:spanCount="@integer/media_columns"/>
+
+        <com.simplemobiletools.gallery.views.FastScroller
+            android:id="@+id/media_fastscroller"
+            android:layout_width="wrap_content"
+            android:layout_height="match_parent"
+            android:layout_alignParentEnd="true"
+            android:layout_alignParentRight="true"
+            android:paddingLeft="@dimen/small_margin"
+            android:paddingRight="@dimen/small_margin"/>
+
+    </RelativeLayout>
 </android.support.v4.widget.SwipeRefreshLayout>

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

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<merge
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="wrap_content"
+    android:layout_height="match_parent">
+
+    <ImageView
+        android:id="@+id/fastscroller_handle"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:background="@drawable/fastscroller_handle"/>
+
+</merge>

app/src/main/res/values/dimens.xml

@@ -8,4 +8,6 @@
     <dimen name="timer_padding">24dp</dimen>
     <dimen name="tmb_shadow_height">50dp</dimen>
     <dimen name="exclude_folder_img_size">48dp</dimen>
+    <dimen name="fastscroll_width">8dp</dimen>
+    <dimen name="fastscroll_height">40dp</dimen>
 </resources>