Use API-compatible activity display lookup

app/src/main/java/com/droiddeck/launcher/SessionActivity.kt

@@ -2017,7 +2017,7 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
 
     private fun refreshSecondScreenDisplays() {
         if (!::displayManager.isInitialized) return
-        val primaryId = display?.displayId ?: windowManager.defaultDisplay.displayId
+        val primaryId = windowManager.defaultDisplay.displayId
         val candidates = SecondScreenDisplays.available(displayManager, primaryId)
         val oldIds = secondScreenDisplays.map { it.id }.toSet()
         secondScreenDisplays = candidates
@@ -2033,7 +2033,7 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
     }
 
     @Suppress("DEPRECATION")
-    private fun currentActivityDisplayId(): Int = display?.displayId ?: windowManager.defaultDisplay.displayId
+    private fun currentActivityDisplayId(): Int = windowManager.defaultDisplay.displayId
 
     private fun refreshActivityDisplayId(): Boolean {
         val current = currentActivityDisplayId()

app/src/main/java/com/droiddeck/launcher/session/SessionService.kt

@@ -1958,7 +1958,7 @@ class SessionService : Service() {
         @Suppress("DEPRECATION")
         private fun currentActivityDisplayId(context: Context): Int {
             val activity = context as? android.app.Activity ?: return Display.DEFAULT_DISPLAY
-            return activity.display?.displayId ?: activity.windowManager.defaultDisplay.displayId
+            return activity.windowManager.defaultDisplay.displayId
         }
 
         fun resume(context: Context) {

app/src/test/java/com/droiddeck/launcher/session/ActivityDisplayCompatibilityTest.kt

@@ -0,0 +1,29 @@
+package com.droiddeck.launcher.session
+
+import android.app.Activity
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.Robolectric
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+@RunWith(RobolectricTestRunner::class)
+@Config(sdk = [26, 28, 29, 33], manifest = Config.NONE)
+class ActivityDisplayCompatibilityTest {
+    @Test fun visibleActivityUsesItsDisplayIdAcrossSupportedAndroidVersions() {
+        val wasRunning = SessionState.running
+        val previousDisplayId = SessionState.activityDisplayId
+        val activity = Robolectric.buildActivity(Activity::class.java).setup().get()
+        try {
+            SessionState.running = false
+            SessionService.setActivityVisible(activity, true)
+
+            assertEquals(activity.windowManager.defaultDisplay.displayId, SessionState.activityDisplayId)
+        } finally {
+            SessionState.running = wasRunning
+            SessionState.activityDisplayId = previousDisplayId
+            activity.finish()
+        }
+    }
+}