From 36cb809cc4241b8bd30bd7cddfddd1a2bb0f1f42 Mon Sep 17 00:00:00 2001
From: Yongshun Shreck Ye <ShreckYe@gmail.com>
Date: Sun, 5 Jan 2025 00:32:04 +0800
Subject: [PATCH] Simplify and improve `previousBackStackEntry` in
 `NavController`

`asReversed` is used instead of `reversed` to reduce the cost of copying a list. The reversed list is converted to a `Sequence` earlier and `drop(1)` is used instead of the iterator to simplify the code.
---
 .../src/main/java/androidx/navigation/NavController.kt | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt b/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt
index 1174a14806bf6..696b1f5c8448c 100644
--- a/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt
+++ b/navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt
@@ -2963,14 +2963,10 @@ public open class NavController(
      *   two visible entries
      */
     public open val previousBackStackEntry: NavBackStackEntry?
-        get() {
-            val iterator = backQueue.reversed().iterator()
+        get() = backQueue.asReversed().asSequence()
             // throw the topmost destination away.
-            if (iterator.hasNext()) {
-                iterator.next()
-            }
-            return iterator.asSequence().firstOrNull { entry -> entry.destination !is NavGraph }
-        }
+            .drop(1)
+            .firstOrNull { entry -> entry.destination !is NavGraph }
 
     public companion object {
         private const val TAG = "NavController"