Support slideshow option on media list

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

@@ -251,11 +251,26 @@ class MediaActivity : SimpleActivity(), MediaOperationsListener {
             R.id.reduce_column_count -> reduceColumnCount()
             R.id.settings -> launchSettings()
             R.id.about -> launchAbout()
+            R.id.slideshow -> startSlideshow()
             else -> return super.onOptionsItemSelected(item)
         }
         return true
     }
 
+    private fun startSlideshow() {
+        if (mMedia.isNotEmpty()) {
+            Intent(this, ViewPagerActivity::class.java).apply {
+                val item = mMedia[0]
+                if (item is Medium) {
+                    putExtra(PATH, item.path)
+                }
+                putExtra(SHOW_ALL, mShowAll)
+                putExtra(SLIDESHOW_START_ON_ENTER, true)
+                startActivity(this)
+            }
+        }
+    }
+
     private fun storeStateVariables() {
         config.apply {
             mStoredAnimateGifs = animateGifs

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

@@ -53,6 +53,8 @@ import java.io.InputStream
 import java.io.OutputStream
 import java.util.*
 
+private val SLIDESHOW_INITED_ON_START_KEY = "SLIDESHOW_INITED_ON_START"
+
 class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, ViewPagerFragment.FragmentListener {
     private var mPath = ""
     private var mDirectory = ""
@@ -68,6 +70,8 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
     private var mSlideshowMoveBackwards = false
     private var mSlideshowMedia = mutableListOf<Medium>()
     private var mAreSlideShowMediaVisible = false
+    private var mSlideshowInitedOnStart = false
+
     private var mIsOrientationLocked = false
 
     private var mMediaFiles = ArrayList<Medium>()
@@ -100,6 +104,23 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
         }
 
         initFavorites()
+        handleSlideshowRequest(savedInstanceState)
+    }
+
+    private fun handleSlideshowRequest(state: Bundle?) {
+        if (intent.getBooleanExtra(SLIDESHOW_START_ON_ENTER, false)) {
+            if (state == null || !state.getBoolean(SLIDESHOW_INITED_ON_START_KEY, false)) {
+                mSlideshowHandler.post {
+                    initSlideshow()
+                }
+            }
+            mSlideshowInitedOnStart = true
+        }
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        outState.putBoolean(SLIDESHOW_INITED_ON_START_KEY, mSlideshowInitedOnStart)
     }
 
     override fun onResume() {
@@ -247,7 +268,6 @@ class ViewPagerActivity : SimpleActivity(), ViewPager.OnPageChangeListener, View
             } else {
                 visibility and View.SYSTEM_UI_FLAG_FULLSCREEN != 0
             }
-
             view_pager.adapter?.let {
                 (it as MyPagerAdapter).toggleFullscreen(mIsFullScreen)
                 checkSystemUI()

app/src/main/kotlin/com/simplemobiletools/gallery/helpers/Constants.kt

@@ -76,6 +76,7 @@ const val SLIDESHOW_MOVE_BACKWARDS = "slideshow_move_backwards"
 const val SLIDESHOW_LOOP = "loop_slideshow"
 const val SLIDESHOW_DEFAULT_INTERVAL = 5
 const val SLIDESHOW_SCROLL_DURATION = 500L
+const val SLIDESHOW_START_ON_ENTER= "slideshow_start_on_enter"
 
 const val NOMEDIA = ".nomedia"
 const val FAVORITES = "favorites"

app/src/main/res/menu/menu_media.xml

@@ -87,4 +87,8 @@
         android:id="@+id/about"
         android:title="@string/about"
         app:showAsAction="never"/>
+    <item
+        android:id="@+id/slideshow"
+        android:title="@string/slideshow"
+        app:showAsAction="never"/>
 </menu>