[WIP] Three Panes (List-List-Detail) Strategy #52

tiwiz · 2025-07-31T17:12:30Z

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Summary of Changes

Hello @tiwiz, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the groundwork for implementing a flexible and adaptive three-pane (List-List-Detail) UI pattern within the application. It introduces core components and strategies that allow the user interface to intelligently adjust its layout based on the available screen real estate, providing an optimized experience across various device form factors.

Highlights

Adaptive Layout Implementation: New DualPaneScene and ThreePaneScene components, along with their respective SceneStrategy implementations, are added to manage multi-pane layouts based on WindowSizeClass. These strategies dynamically determine how many panes to display (one, two, or three) based on the available screen width.
New Three-Pane Activity Example: A ThreePanesActivity is introduced as a practical example of how to integrate the new adaptive navigation strategies. This activity demonstrates a List-List-Detail flow, where the UI adapts from a single pane to a dual-pane or three-pane layout as the window size increases.
Dependency Updates and Additions: The project's build.gradle.kts file has been updated to include androidx.window and androidx.window.core dependencies, which are crucial for adaptive layouts. Additionally, several existing dependencies, including Kotlin, Compose BOM, and Navigation3, have been updated to their latest versions.

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Code Review

This pull request introduces a new three-pane layout strategy, which is a great addition for adaptive UIs. The implementation is a good starting point. My review includes a critical fix for a UI bug in the list display, along with several suggestions to improve code clarity, maintainability, and documentation accuracy. These include correcting KDocs, removing redundant dependencies and code, and adopting more idiomatic Kotlin constructs.

gemini-code-assist · 2025-07-31T17:14:59Z

app/build.gradle.kts

@@ -71,6 +71,8 @@ dependencies {
    implementation(libs.androidx.material3.windowsizeclass)
    implementation(libs.androidx.adaptive.layout)
    implementation(libs.androidx.material3.navigation3)
+    implementation(libs.androidx.window)
+    implementation(libs.androidx.window.core)


The androidx.window:window-core dependency is a transitive dependency of androidx.window. You only need to declare the androidx.window dependency. Including redundant dependencies can make dependency management more complex and is generally discouraged.

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/DualPaneScene.kt

+ * A [SceneStrategy] that always creates a 1-entry [Scene] simply displaying the last entry in the
+ * list.
+ */


The KDoc for DualPaneSceneStrategy is inaccurate. It states that it always creates a "1-entry [Scene]", but it actually creates a DualPaneScene which contains two entries when screen width and back stack depth conditions are met. Please update the documentation to reflect the actual behavior.

Suggested change

* A [SceneStrategy] that always creates a 1-entry [Scene] simply displaying the last entry in the

* list.

*/

* A [SceneStrategy] that creates a [DualPaneScene] when the window width is medium or larger

* and there are at least two entries in the back stack.

*/

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/ThreePaneActivity.kt

+ * Basic example with two screens that uses the entryProvider DSL and has a persistent back stack.
+ */


The KDoc for ThreePanesActivity appears to be copied from another example. It mentions "two screens", but this activity demonstrates a three-pane layout. Please update the documentation to be accurate.

Suggested change

* Basic example with two screens that uses the entryProvider DSL and has a persistent back stack.

*/

* Basic example that demonstrates a three-pane layout strategy.

*/

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/ThreePaneScene.kt

+import androidx.navigation3.ui.SceneStrategy
+import androidx.window.core.layout.WindowSizeClass
+import androidx.window.core.layout.WindowSizeClass.Companion.WIDTH_DP_LARGE_LOWER_BOUND
+import androidx.window.core.layout.WindowSizeClass.Companion.WIDTH_DP_MEDIUM_LOWER_BOUND


The import androidx.window.core.layout.WindowSizeClass.Companion.WIDTH_DP_MEDIUM_LOWER_BOUND is unused in this file and can be removed to improve code cleanliness.

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/ThreePaneScene.kt

+    private fun computeEntriesAndEmptyState() : Triple<NavEntry<T>, NavEntry<T>?, NavEntry<T>?> {
+        if(entries.size >= 3) {
+            return Triple(entries[entries.lastIndex - 2], entries[entries.lastIndex - 1], entries.last())
+        } else if(entries.size == 2) {
+            return Triple(entries[entries.lastIndex - 1], entries.last(), null)
+        } else {
+            return Triple(entries.last(), null, null)
+        }
+    }


This if-else if-else chain can be replaced with a when expression, which is more idiomatic and generally more readable in Kotlin.

private fun computeEntriesAndEmptyState() : Triple<NavEntry<T>, NavEntry<T>?, NavEntry<T>?> { return when { entries.size >= 3 -> Triple(entries[entries.lastIndex - 2], entries[entries.lastIndex - 1], entries.last()) entries.size == 2 -> Triple(entries.first(), entries.last(), null) else -> Triple(entries.first(), null, null) } }

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/ThreePaneScene.kt

+ * A [SceneStrategy] that always creates a 1-entry [Scene] simply displaying the last entry in the
+ * list.
+ */


The KDoc for ThreePaneSceneStrategy is inaccurate and seems to be copied from another class. It should describe that this strategy creates a ThreePaneScene for large-width windows.

* A [SceneStrategy] that creates a [ThreePaneScene] when the window width is large. The * [ThreePaneScene] can display one, two, or three panes depending on the back stack depth. */

gemini-code-assist · 2025-07-31T17:14:59Z

app/src/main/java/com/example/nav3recipes/scenes/threepanes/ThreePaneScene.kt

+/*
+@Composable
+internal fun <T : Any> SceneStrategy<T>.calculateSceneWithSinglePaneFallback(
+    entries: List<NavEntry<T>>,
+    onBack: (count: Int) -> Unit,
+): Scene<T> =
+    calculateScene(entries, onBack) ?: ThreePaneSceneStrategy<T>().calculateScene(entries, onBack)
+*/


This commented-out code should be removed before merging to keep the codebase clean and avoid confusion.

gemini-code-assist · 2025-07-31T17:15:00Z

gradle/libs.versions.toml

@@ -59,6 +60,8 @@ kotlinx-serialization-core = { module = "org.jetbrains.kotlinx:kotlinx-serializa
 kotlinx-serialization-json = { module = "org.jetbrains.kotlinx:kotlinx-serialization-json", version.ref = "kotlinxSerializationCore" }
 androidx-material-icons-extended = { group = "androidx.compose.material", name = "material-icons-extended" }
 androidx-material3-navigation3 = { group = "androidx.compose.material3.adaptive", name = "adaptive-navigation3", version.ref = "nav3Material" }
+androidx-window = { group = "androidx.window", name = "window", version.ref = "window" }
+androidx-window-core = { group = "androidx.window", name = "window-core", version.ref = "window" }


The androidx-window-core library is a transitive dependency of androidx-window. It's good practice to only declare direct dependencies in your Gradle files. Since androidx.window.core is not needed directly, you can remove this line. Remember to also remove the corresponding implementation from app/build.gradle.kts.

Started strategy for Three Panes List-List-Detail

0b50b1b

tiwiz marked this pull request as ready for review July 31, 2025 17:12

tiwiz requested a review from dturner as a code owner July 31, 2025 17:12

gemini-code-assist bot reviewed Jul 31, 2025

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tiwiz changed the title ~~Started strategy for Three Panes List-List-Detail~~ [WIP] Three Panes (List-List-Detail) Strategy Jul 31, 2025

gemini-code-assist bot reviewed Jul 31, 2025

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[WIP] Three Panes (List-List-Detail) Strategy #52

[WIP] Three Panes (List-List-Detail) Strategy #52

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- * A [SceneStrategy] that always creates a 1-entry [Scene] simply displaying the last entry in the
- * list.
- */
+ * A [SceneStrategy] that creates a [DualPaneScene] when the window width is medium or larger
+ * and there are at least two entries in the back stack.
+ */

		* Basic example with two screens that uses the entryProvider DSL and has a persistent back stack.
		*/

[WIP] Three Panes (List-List-Detail) Strategy #52

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