implement the Add and Remove favorite buttons

app/src/main/kotlin/com/simplemobiletools/filemanager/Config.kt

@@ -4,6 +4,7 @@ import android.content.Context
 import com.simplemobiletools.commons.extensions.getInternalStoragePath
 import com.simplemobiletools.commons.helpers.BaseConfig
 import java.io.File
+import java.util.*
 
 class Config(context: Context) : BaseConfig(context) {
     companion object {
@@ -23,4 +24,20 @@ class Config(context: Context) : BaseConfig(context) {
             return home
         }
         set(homeFolder) = prefs.edit().putString(HOME_FOLDER, homeFolder).apply()
+
+    fun addFavorite(path: String) {
+        val currFavorites = HashSet<String>(favorites)
+        currFavorites.add(path)
+        favorites = currFavorites
+    }
+
+    fun removeFavorite(path: String) {
+        val currFavorites = HashSet<String>(favorites)
+        currFavorites.remove(path)
+        favorites = currFavorites
+    }
+
+    var favorites: MutableSet<String>
+        get() = prefs.getStringSet(FAVORITES, HashSet<String>())
+        set(favorites) = prefs.edit().remove(FAVORITES).putStringSet(FAVORITES, favorites).apply()
 }

app/src/main/kotlin/com/simplemobiletools/filemanager/Constants.kt

@@ -6,3 +6,4 @@ val SCROLL_STATE = "scroll_state"
 // shared preferences
 val SHOW_HIDDEN = "show_hidden"
 val HOME_FOLDER = "home_folder"
+val FAVORITES = "favorites"

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

@@ -29,6 +29,7 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
     var latestFragment: ItemsFragment? = null
     var mScrollStates = HashMap<String, Parcelable>()
     var mStoredTextColor = 0
+    var currentPath = ""
 
     companion object {
         private val STORAGE_PERMISSION = 1
@@ -52,7 +53,7 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
         if (mStoredTextColor != config.textColor) {
             mStoredTextColor = config.textColor
             breadcrumbs.setTextColor(mStoredTextColor)
-            openPath(getCurrenPath())
+            openPath(currentPath)
         }
     }
 
@@ -96,10 +97,17 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
             setListener(this@MainActivity)
             supportFragmentManager.beginTransaction().replace(R.id.fragment_holder, this).addToBackStack(path).commitAllowingStateLoss()
         }
+        currentPath = path
+        invalidateOptionsMenu()
     }
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.menu, menu)
+
+        val favorites = config.favorites
+        menu.findItem(R.id.add_favorite).isVisible = !favorites.contains(currentPath)
+        menu.findItem(R.id.remove_favorite).isVisible = favorites.contains(currentPath)
+
         return true
     }
 
@@ -121,20 +129,20 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
     }
 
     private fun addFavorite() {
-
+        config.addFavorite(currentPath)
+        invalidateOptionsMenu()
     }
 
     private fun removeFavorite() {
-
+        config.removeFavorite(currentPath)
+        invalidateOptionsMenu()
     }
 
     private fun setAsHome() {
-        config.homeFolder = getCurrenPath()
+        config.homeFolder = currentPath
         toast(R.string.home_folder_updated)
     }
 
-    private fun getCurrenPath() = (breadcrumbs.getChildAt(breadcrumbs.childCount - 1).tag as FileDirItem).path.trimEnd('/')
-
     private fun launchAbout() {
         startAboutActivity(R.string.app_name, LICENSE_KOTLIN or LICENSE_MULTISELECT, BuildConfig.VERSION_NAME)
     }
@@ -174,7 +182,7 @@ class MainActivity : SimpleActivity(), ItemsFragment.ItemInteractionListener, Br
 
     override fun breadcrumbClicked(id: Int) {
         if (id == 0) {
-            StoragePickerDialog(this@MainActivity, getCurrenPath()) {
+            StoragePickerDialog(this@MainActivity, currentPath) {
                 openPath(it)
             }
         } else {