Options sortByWord and sortByTranslation are available

app/src/main/java/com/paktalin/vocabularynotebook/VocabularyAdapter.kt

@@ -11,10 +11,12 @@ import android.widget.LinearLayout
 import android.widget.TextView
 import com.paktalin.vocabularynotebook.ui.EditWordFragment
 import com.paktalin.vocabularynotebook.ui.MainActivity
+import java.util.*
 
 class VocabularyAdapter(private val wordItems: MutableList<WordItem>, private val activity: Activity) : RecyclerView.Adapter<VocabularyAdapter.ViewHolder>() {
 
     private lateinit var recyclerView: RecyclerView
+    private var sortByWord = true
 
     override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
         super.onAttachedToRecyclerView(recyclerView)
@@ -68,6 +70,26 @@ class VocabularyAdapter(private val wordItems: MutableList<WordItem>, private va
         this.notifyDataSetChanged()
     }
 
+    private fun sortByTranslation() {
+        wordItems.sortWith(Comparator { item1, item2 ->
+            item1.pojo!!.translation!!.compareTo(item2.pojo!!.translation!!)
+        })
+        this.notifyDataSetChanged()
+    }
+
+    private fun sortByWord() {
+        wordItems.sortWith(Comparator { item1, item2 ->
+            item1.pojo!!.word!!.compareTo(item2.pojo!!.word!!)
+        })
+        this.notifyDataSetChanged()
+    }
+
+    fun sort() {
+        sortByWord = !sortByWord
+        if (sortByWord) sortByWord()
+        else sortByTranslation()
+    }
+
     @SuppressLint("ResourceType")
     private fun editWordItem(container:View, wordItem: WordItem) {
         //set container id

app/src/main/java/com/paktalin/vocabularynotebook/pojo/VocabularyPojo.java

@@ -2,7 +2,7 @@ package com.paktalin.vocabularynotebook.pojo;
 
 public class VocabularyPojo {
 
-    String title;
+    private String title;
 
     public VocabularyPojo() {
         title = "First vocabulary";

app/src/main/java/com/paktalin/vocabularynotebook/ui/MainActivity.kt

@@ -15,7 +15,9 @@ import android.view.Menu
 import android.view.MenuItem
 import android.view.View
 import android.view.inputmethod.InputMethodManager
+import com.paktalin.vocabularynotebook.VocabularyAdapter
 import com.paktalin.vocabularynotebook.appsetup.ConfiguredFirestore
+import kotlinx.android.synthetic.main.fragment_vocabulary.*
 
 class MainActivity : AppCompatActivity() {
 
@@ -38,7 +40,7 @@ class MainActivity : AppCompatActivity() {
 
     override fun onOptionsItemSelected(item: MenuItem?): Boolean {
         if (item!!.itemId == R.id.sort)
-            Log.d(TAG, "sort")
+            (recyclerView.adapter as VocabularyAdapter).sort()
         return super.onOptionsItemSelected(item)
     }
 

app/src/main/java/com/paktalin/vocabularynotebook/ui/VocabularyFragment.kt

@@ -43,7 +43,7 @@ class VocabularyFragment : Fragment() {
     }
 
     fun retrieveWordsData(vocabularyId: String) {
-        db.collection(VOCABULARIES).document(vocabularyId).collection(WORDS).get()
+        db.collection(VOCABULARIES).document(vocabularyId).collection(WORDS).orderBy("word").get()
                 .addOnSuccessListener { setVocabularyAdapter(it.documents, vocabularyId) }
     }