DialogCollator destroys/rebuild instead of dismiss/show

When `DialogCollator` has to reorder, it did so by calling `Dialog.dismiss()` and `Dialog.show()`. When that happens the view in the `Dialog` is detached from its window and reattached. When that view is a `ComposeView`, it stops acknowledging touch events.

This is the umpteenth bug we've faced because views tend to be written assuming they will only ever be attached once, and I'm tired of it, so now we destroy a dialog that is out of order and create a new one to replace it -- taking care to save the view state of the destroyed one and restore it on the replacement.

workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/navigation/DialogCollator.kt

@@ -1,9 +1,11 @@
 package com.squareup.workflow1.ui.navigation
 
+import com.squareup.workflow1.ui.Compatible
 import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.ViewEnvironmentKey
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 import com.squareup.workflow1.ui.navigation.DialogCollator.IdAndSessions
+import com.squareup.workflow1.ui.navigation.DialogSession.KeyAndBundle
 import java.util.UUID
 
 /**
@@ -38,7 +40,11 @@ internal class DialogSessionUpdate(
     oldSessionFinder: OldSessionFinder,
     covered: Boolean
   ) -> DialogSession
-)
+) {
+  override fun toString(): String {
+    return "DialogSessionUpdate(overlay=${Compatible.keyFor(overlay)})"
+  }
+}
 
 /**
  * Init method called at the start of [LayeredDialogSessions.update].
@@ -113,8 +119,7 @@ internal fun ViewEnvironment.establishDialogCollator(
  * updates that were enqueued with the shared [DialogCollator] are executed in a single
  * pass. Because this [DialogCollator] has complete knowledge of the existing stack
  * of `Dialog` windows and all updates, it is able to decide if any existing instances need to be
- * [dismissed][android.app.Dialog.dismiss] and [re-shown][android.app.Dialog.show]
- * to keep them in the correct order.
+ * [destroyed][DialogSession.destroyDialog] and rebuilt to keep them in the correct order.
  */
 @WorkflowUiExperimentalApi
 internal class DialogCollator {
@@ -149,7 +154,11 @@ internal class DialogCollator {
     val id: UUID,
     val updates: List<DialogSessionUpdate>,
     val onSessionsUpdated: (List<DialogSession>) -> Unit
-  )
+  ) {
+    override fun toString(): String {
+      return "IdAndUpdates(id=$id, updates=$updates)"
+    }
+  }
 
   /**
    * The [IdAndUpdates] instances accumulated by all calls to [scheduleUpdates].
@@ -199,10 +208,6 @@ internal class DialogCollator {
         .flatMap { it.sessions.map { session -> Pair(it.id, session) } }
         .iterator()
 
-    // Collects members of establishedSessions that are dismissed because they
-    // are out of order, so that we can try to show them again.
-    val hiddenSessions = mutableListOf<Pair<UUID, DialogSession>>()
-
     // Z index of the uppermost ModalOverlay.
     val topModalIndex = allUpdates.asSequence()
       .flatMap { it.updates.asSequence().map { update -> update.overlay } }
@@ -212,14 +217,13 @@ internal class DialogCollator {
     var updatingSessionIndex = 0
 
     val allNewSessions = mutableListOf<DialogSession>()
+    val viewStates = mutableMapOf<String, KeyAndBundle>()
     allUpdates.forEach { idAndUpdates ->
       val updatedSessions = mutableListOf<DialogSession>()
 
       // We're building an object that the next LayeredDialogSessions can use to
       // find an existing dialog that matches a given Overlay. Any
-      // incompatible dialog that we skip on the way to find a match is dismissed.
-      // If we later find a match for one of the dismissed dialogs, it is re-shown --
-      // which moves it to the front, ensuring the correct Z order.
+      // incompatible dialog that we skip on the way to find a match is destroyed.
       val oldSessionFinder = OldSessionFinder { overlay ->
 
         // First we iterate through the existing windows to find one that belongs
@@ -228,26 +232,23 @@ internal class DialogCollator {
           val (id, session) = establishedSessionsIterator.next()
           if (idAndUpdates.id == id && session.canShow(overlay)) return@OldSessionFinder session
 
-          // Can't update this session from this Overlay. Dismiss it (via Dialog.dismiss
-          // under the hood), but hold on to it in case it can except a later Overlay.
-          session.setVisible(false)
-          hiddenSessions.add(Pair(id, session))
+          // Can't update this session from this Overlay, save its view state and destroy it.
+          // It it was just out of z order, a new one with matching id will be made and restored.
+          session.save()?.let { viewStates[id.toString() + session.savedStateKey] = it }
+          session.destroyDialog(andSaveViewState = true)
           continue
         }
 
-        // There are no established windows left. See if any of the ones that were
-        // dismissed because they were out of order can be shown again.
-        return@OldSessionFinder hiddenSessions.indexOfFirst { (hiddenId, dialogSession) ->
-          idAndUpdates.id == hiddenId && dialogSession.canShow(overlay)
-        }.takeUnless { it == -1 }?.let { compatibleIndex ->
-          val restoredSession = hiddenSessions.removeAt(compatibleIndex).second
-          restoredSession.apply { setVisible(true) }
-        }
+        // There are no established windows left.
+        return@OldSessionFinder null
       }
 
       idAndUpdates.updates.forEach { update ->
         val covered = updatingSessionIndex < topModalIndex
-        updatedSessions += update.doUpdate(oldSessionFinder, covered)
+        updatedSessions += update.doUpdate(oldSessionFinder, covered).also { session ->
+          viewStates.remove(idAndUpdates.id.toString() + session.savedStateKey)
+            ?.let { session.restore(it) }
+        }
         updatingSessionIndex++
       }
       idAndUpdates.onSessionsUpdated(updatedSessions)

workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/navigation/DialogSession.kt

@@ -5,9 +5,6 @@ import android.os.Parcel
 import android.os.Parcelable
 import android.os.Parcelable.Creator
 import android.view.KeyEvent
-import android.view.KeyEvent.ACTION_UP
-import android.view.KeyEvent.KEYCODE_BACK
-import android.view.KeyEvent.KEYCODE_ESCAPE
 import android.view.MotionEvent
 import android.view.Window.Callback
 import androidx.activity.OnBackPressedDispatcher
@@ -94,9 +91,6 @@ internal class DialogSession(
    */
   val savedStateKey = Compatible.keyFor(initialOverlay)
 
-  private val KeyEvent.isBackPress: Boolean
-    get() = (keyCode == KEYCODE_BACK || keyCode == KEYCODE_ESCAPE) && action == ACTION_UP
-
   /**
    * One time call to set up our brand new [OverlayDialogHolder] instance.
    * This will be followed by one time calls to [showNewDialog] and [destroyDialog].
@@ -242,10 +236,11 @@ internal class DialogSession(
    * We are never going to use this `Dialog` again. Tear down our lifecycle hooks
    * and dismiss it.
    */
-  fun destroyDialog() {
+  fun destroyDialog(andSaveViewState: Boolean = false) {
     if (!destroyed) {
       destroyed = true
       with(holder.dialog) {
+        if (andSaveViewState) stateRegistryAggregator.saveAndPruneChildRegistryOwner(savedStateKey)
         // The dialog's views are about to be detached, and when that happens we want to transition
         // the dialog view's lifecycle to a terminal state even though the parent is probably still
         // alive.