New: Update to 1.2.0 version of RecyclerView to take advantage of new StateRestorationPolicy

which automatically handles some of the more complex state management. Without this change, the recyclerview would lose its scroll position after viewing tx details. Now it handles it perfectly due to setting transactionAdapter.stateRestorationPolicy =
            RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY

app/build.gradle

@@ -119,6 +119,7 @@ dependencies {
     implementation Deps.AndroidX.FRAGMENT_KTX
     implementation Deps.AndroidX.LEGACY
     implementation Deps.AndroidX.PAGING
+    implementation Deps.AndroidX.RECYCLER
     implementation Deps.AndroidX.CameraX.CAMERA2
     implementation Deps.AndroidX.CameraX.CORE
     implementation Deps.AndroidX.CameraX.LIFECYCLE

app/src/main/java/cash/z/ecc/android/ui/history/HistoryFragment.kt

@@ -6,8 +6,12 @@ import android.view.View
 import androidx.lifecycle.lifecycleScope
 import androidx.paging.PagedList
 import androidx.recyclerview.widget.LinearLayoutManager
+import androidx.recyclerview.widget.RecyclerView
 import cash.z.ecc.android.R
 import cash.z.ecc.android.databinding.FragmentHistoryBinding
+import cash.z.ecc.android.di.viewmodel.activityViewModel
+import cash.z.ecc.android.ext.goneIf
+import cash.z.ecc.android.ext.onClickNavUp
 import cash.z.ecc.android.ext.toColoredSpan
 import cash.z.ecc.android.feedback.Report
 import cash.z.ecc.android.feedback.Report.Tap.HISTORY_BACK
@@ -26,6 +30,9 @@ class HistoryFragment : BaseFragment<FragmentHistoryBinding>() {
 
     private val viewModel: HistoryViewModel by activityViewModel()
 
+    private lateinit var transactionAdapter: TransactionAdapter<ConfirmedTransaction>
+
+    private var isInitialized = false
 
     override fun inflate(inflater: LayoutInflater): FragmentHistoryBinding =
         FragmentHistoryBinding.inflate(inflater)
@@ -34,6 +41,7 @@ class HistoryFragment : BaseFragment<FragmentHistoryBinding>() {
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         twig("HistoryFragment.onViewCreated")
         super.onViewCreated(view, savedInstanceState)
+        initTransactionUI()
         binding.backButtonHitArea.onClickNavUp { tapped(HISTORY_BACK) }
         lifecycleScope.launch {
             binding.textAddress.text = viewModel.getAddress().toAbbreviatedAddress()
@@ -43,10 +51,10 @@ class HistoryFragment : BaseFragment<FragmentHistoryBinding>() {
     override fun onResume() {
         twig("HistoryFragment.onResume")
         super.onResume()
-        initTransactionUI()
         viewModel.balance.collectWith(resumedScope) {
             onBalanceUpdated(it)
         }
+        viewModel.transactions.collectWith(resumedScope) { onTransactionsUpdated(it) }
     }
 
     private fun onBalanceUpdated(balance: WalletBalance) {
@@ -60,29 +68,25 @@ class HistoryFragment : BaseFragment<FragmentHistoryBinding>() {
     }
 
     private fun initTransactionUI() {
-        adapter = TransactionAdapter()
+        twig("HistoryFragment.initTransactionUI")
+        transactionAdapter = TransactionAdapter()
+        transactionAdapter.stateRestorationPolicy =
+            RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY
+
         binding.recyclerTransactions.apply {
-            layoutManager =
-                LinearLayoutManager(activity, LinearLayoutManager.VERTICAL, false)
+            layoutManager = LinearLayoutManager(activity, LinearLayoutManager.VERTICAL, false)
             addItemDecoration(TransactionsFooter(binding.recyclerTransactions.context))
-            adapter = this@WalletDetailFragment.adapter
-            scrollToTop()
+            adapter = transactionAdapter
         }
-        viewModel.transactions.collectWith(resumedScope) { onTransactionsUpdated(it) }
     }
 
     private fun onTransactionsUpdated(transactions: PagedList<ConfirmedTransaction>) {
         twig("HistoryFragment.onTransactionsUpdated")
         transactions.size.let { newCount ->
+            twig("got a new paged list of transactions of length $newCount")
             binding.groupEmptyViews.goneIf(newCount > 0)
-            val preSize = adapter.itemCount
-            adapter.submitList(transactions)
-            // don't rescroll while the user is looking at the list, unless it's initialization
-            // using 4 here because there might be headers or other things that make 0 a bad pick
-            // 4 is about how many can fit before scrolling becomes necessary on many screens
-            if (preSize < 4 && newCount > preSize) {
-                scrollToTop()
-            }
+            val preSize = transactionAdapter.itemCount
+            transactionAdapter.submitList(transactions)
         }
     }
 

app/src/main/java/cash/z/ecc/android/ui/history/TransactionAdapter.kt

@@ -24,6 +24,10 @@ class TransactionAdapter<T : ConfirmedTransaction> :
         }
     ) {
 
+    init {
+        setHasStableIds(true)
+    }
+
     override fun onCreateViewHolder(
         parent: ViewGroup,
         viewType: Int
@@ -35,4 +39,8 @@ class TransactionAdapter<T : ConfirmedTransaction> :
         holder: TransactionViewHolder<T>,
         position: Int
     ) = holder.bindTo(getItem(position))
+
+    override fun getItemId(position: Int): Long {
+        return getItem(position)?.id ?: -1
+    }
 }

buildSrc/src/main/java/cash/z/ecc/android/Dependencies.kt

@@ -20,6 +20,7 @@ object Deps {
         const val LEGACY =                  "androidx.legacy:legacy-support-v4:1.0.0"
         const val MULTIDEX =                "androidx.multidex:multidex:2.0.1"
         const val PAGING =                  "androidx.paging:paging-runtime-ktx:2.1.2"
+        const val RECYCLER =                "androidx.recyclerview:recyclerview:1.2.0-alpha05"
         object CameraX :         Version("1.0.0-beta04") {
             val CAMERA2 =                   "androidx.camera:camera-camera2:1.0.0-beta04"
             val CORE =                      "androidx.camera:camera-core:1.0.0-beta04"