Add custom finishing behaviors for split pair

Add support for custom finishing behaviors for containers in split
pairs. 'finishPrimaryWithSecondary' and 'finishSecondaryWithPrimary'
now have several options:
- never
- always
- adjacent (finish only when containers are shown side by side, but
not when stacked).

'finishPrimaryWithSecondary' option was also added to placeholder
rules.

Bug: 204829538
Test: Manual, using demo app and Settings.
Change-Id: I543d15e62acc57f9ad6578221248fbb0a8c719db

libs/WindowManager/Jetpack/src/androidx/window/extensions/embedding/SplitContainer.java

@@ -73,17 +73,48 @@ class SplitContainer {
     static boolean shouldFinishPrimaryWithSecondary(@NonNull SplitRule splitRule) {
         final boolean isPlaceholderContainer = splitRule instanceof SplitPlaceholderRule;
         final boolean shouldFinishPrimaryWithSecondary = (splitRule instanceof SplitPairRule)
-                && ((SplitPairRule) splitRule).shouldFinishPrimaryWithSecondary();
+                && ((SplitPairRule) splitRule).getFinishPrimaryWithSecondary()
+                != SplitRule.FINISH_NEVER;
         return shouldFinishPrimaryWithSecondary || isPlaceholderContainer;
     }
 
     static boolean shouldFinishSecondaryWithPrimary(@NonNull SplitRule splitRule) {
         final boolean isPlaceholderContainer = splitRule instanceof SplitPlaceholderRule;
         final boolean shouldFinishSecondaryWithPrimary = (splitRule instanceof SplitPairRule)
-                && ((SplitPairRule) splitRule).shouldFinishSecondaryWithPrimary();
+                && ((SplitPairRule) splitRule).getFinishSecondaryWithPrimary()
+                != SplitRule.FINISH_NEVER;
         return shouldFinishSecondaryWithPrimary || isPlaceholderContainer;
     }
 
+    static boolean shouldFinishAssociatedContainerWhenStacked(int finishBehavior) {
+        return finishBehavior == SplitRule.FINISH_ALWAYS;
+    }
+
+    static boolean shouldFinishAssociatedContainerWhenAdjacent(int finishBehavior) {
+        return finishBehavior == SplitRule.FINISH_ALWAYS
+                || finishBehavior == SplitRule.FINISH_ADJACENT;
+    }
+
+    static int getFinishPrimaryWithSecondaryBehavior(@NonNull SplitRule splitRule) {
+        if (splitRule instanceof SplitPlaceholderRule) {
+            return ((SplitPlaceholderRule) splitRule).getFinishPrimaryWithSecondary();
+        }
+        if (splitRule instanceof SplitPairRule) {
+            return ((SplitPairRule) splitRule).getFinishPrimaryWithSecondary();
+        }
+        return SplitRule.FINISH_NEVER;
+    }
+
+    static int getFinishSecondaryWithPrimaryBehavior(@NonNull SplitRule splitRule) {
+        if (splitRule instanceof SplitPlaceholderRule) {
+            return SplitRule.FINISH_ALWAYS;
+        }
+        if (splitRule instanceof SplitPairRule) {
+            return ((SplitPairRule) splitRule).getFinishSecondaryWithPrimary();
+        }
+        return SplitRule.FINISH_NEVER;
+    }
+
     static boolean isStickyPlaceholderRule(@NonNull SplitRule splitRule) {
         if (!(splitRule instanceof SplitPlaceholderRule)) {
             return false;

libs/WindowManager/Jetpack/src/androidx/window/extensions/embedding/SplitController.java

@@ -16,7 +16,11 @@
 
 package androidx.window.extensions.embedding;
 
+import static androidx.window.extensions.embedding.SplitContainer.getFinishPrimaryWithSecondaryBehavior;
+import static androidx.window.extensions.embedding.SplitContainer.getFinishSecondaryWithPrimaryBehavior;
 import static androidx.window.extensions.embedding.SplitContainer.isStickyPlaceholderRule;
+import static androidx.window.extensions.embedding.SplitContainer.shouldFinishAssociatedContainerWhenAdjacent;
+import static androidx.window.extensions.embedding.SplitContainer.shouldFinishAssociatedContainerWhenStacked;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
@@ -665,15 +669,21 @@ public class SplitController implements JetpackTaskFragmentOrganizer.TaskFragmen
             // Containers are not in the same split, no need to retain.
             return false;
         }
-
-        if (!isStickyPlaceholderRule(splitContainer.getSplitRule())) {
-            // Currently only the containers associated with sticky placeholders can be retained.
-            return false;
+        // Find the finish behavior for the associated container
+        int finishBehavior;
+        SplitRule splitRule = splitContainer.getSplitRule();
+        if (finishingContainer == splitContainer.getPrimaryContainer()) {
+            finishBehavior = getFinishSecondaryWithPrimaryBehavior(splitRule);
+        } else {
+            finishBehavior = getFinishPrimaryWithSecondaryBehavior(splitRule);
+        }
+        // Decide whether the associated container should be retained based on the current
+        // presentation mode.
+        if (mPresenter.shouldShowSideBySide(splitContainer)) {
+            return !shouldFinishAssociatedContainerWhenAdjacent(finishBehavior);
+        } else {
+            return !shouldFinishAssociatedContainerWhenStacked(finishBehavior);
         }
-
-        // When sticky placeholder is stacked on top of the main container it should not cause the
-        // destruction of the primary one.
-        return !mPresenter.shouldShowSideBySide(splitContainer);
     }
 
     /**