Implement "stable ID" for candidate adapters

prevent crash in FlexboxLayoutManager and hopefully improves performance
ref: https://github.com/google/flexbox-layout/issues/363#issuecomment-382949953

app/src/main/java/org/fcitx/fcitx5/android/input/candidates/floating/PagedCandidatesUi.kt

@@ -43,6 +43,13 @@ class PagedCandidatesUi(
     }
 
     private val candidatesAdapter = object : RecyclerView.Adapter<UiHolder>() {
+        init {
+            setHasStableIds(true)
+        }
+
+        override fun getItemId(position: Int): Long =
+            data.candidates[position].hashCode().toLong()
+
         override fun getItemCount() =
             data.candidates.size + (if (data.hasPrev || data.hasNext) 1 else 0)
 
@@ -98,6 +105,7 @@ class PagedCandidatesUi(
         adapter = candidatesAdapter
         layoutManager = candidatesLayoutManager
         overScrollMode = View.OVER_SCROLL_NEVER
+        itemAnimator = null
     }
 
     @SuppressLint("NotifyDataSetChanged")

app/src/main/java/org/fcitx/fcitx5/android/input/candidates/horizontal/HorizontalCandidateComponent.kt

@@ -163,6 +163,7 @@ class HorizontalCandidateComponent :
             }
         }.apply {
             id = R.id.candidate_view
+            itemAnimator = null
             adapter = this@HorizontalCandidateComponent.adapter
             layoutManager = this@HorizontalCandidateComponent.layoutManager
             addItemDecoration(FlexboxVerticalDecoration(dividerDrawable))

app/src/main/java/org/fcitx/fcitx5/android/input/candidates/horizontal/HorizontalCandidateViewAdapter.kt

@@ -21,6 +21,10 @@ import splitties.views.setPaddingDp
 open class HorizontalCandidateViewAdapter(val theme: Theme) :
     RecyclerView.Adapter<CandidateViewHolder>() {
 
+    init {
+        setHasStableIds(true)
+    }
+
     var candidates: Array<String> = arrayOf()
         private set
 
@@ -36,6 +40,10 @@ open class HorizontalCandidateViewAdapter(val theme: Theme) :
 
     override fun getItemCount() = candidates.size
 
+    override fun getItemId(position: Int): Long {
+        return candidates[position].hashCode().toLong()
+    }
+
     @CallSuper
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CandidateViewHolder {
         val ui = CandidateItemUi(parent.context, theme)