[MOBILE-3601] Fix pager page actions (#1226)

* Fix actions for initial pager page displays

* Update PagerModelTest

* spots

Author: jyaganeh

urbanairship-layout/src/main/java/com/urbanairship/android/layout/model/PagerModel.kt

@@ -18,6 +18,8 @@ import com.urbanairship.android.layout.property.ViewType
 import com.urbanairship.android.layout.util.pagerScrolls
 import com.urbanairship.android.layout.view.PagerView
 import com.urbanairship.json.JsonValue
+import kotlinx.coroutines.flow.filter
+import kotlinx.coroutines.flow.map
 import kotlinx.coroutines.launch
 
 internal class PagerModel(
@@ -82,6 +84,25 @@ internal class PagerModel(
         pagerState.update { state ->
             state.copyWithPageIds(pageIds = items.map { it.identifier })
         }
+
+        // Listen for page changes (or the initial page display)
+        // and run any actions for the current page.
+        modelScope.launch {
+
+            pagerState.changes
+                .map { it.pageIndex to it.lastPageIndex }
+                .filter { (pageIndex, lastPageIndex) ->
+                    // If current and last are both 0, we're initializing the pager.
+                    // Otherwise, we only want to act on changes to the pageIndex.
+                    pageIndex == 0 && lastPageIndex == 0 || pageIndex != lastPageIndex
+                }
+                .collect { (pageIndex, _) ->
+                    // Run any actions for the current page.
+                    items[pageIndex].actions?.let { actions ->
+                        runActions(actions)
+                    }
+                }
+        }
     }
 
     override fun onCreateView(context: Context, viewEnvironment: ViewEnvironment) =
@@ -90,12 +111,15 @@ internal class PagerModel(
         }
 
     override fun onViewAttached(view: PagerView) {
+        // Collect page index changes from state and tell the view to scroll to the current page.
         viewScope.launch {
             pagerState.changes.collect {
                 listener?.scrollTo(it.pageIndex)
             }
         }
 
+        // Collect pager scrolls, update pager state, and report
+        // the page swipe if it was triggered by the user.
         viewScope.launch {
             view.pagerScrolls().collect { (position, isInternalScroll) ->
                 pagerState.update { state ->
@@ -105,11 +129,6 @@ internal class PagerModel(
                 if (!isInternalScroll) {
                     reportPageSwipe(pagerState.changes.value)
                 }
-
-                // Run any actions for the current page.
-                items[position].actions?.let { actions ->
-                    runActions(actions)
-                }
             }
         }
     }

urbanairship-layout/src/test/java/com/urbanairship/android/layout/model/PagerModelTest.kt

@@ -19,8 +19,10 @@ import io.mockk.verify
 import kotlinx.coroutines.ExperimentalCoroutinesApi
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.test.StandardTestDispatcher
 import kotlinx.coroutines.test.TestResult
 import kotlinx.coroutines.test.TestScope
+import kotlinx.coroutines.test.runCurrent
 import kotlinx.coroutines.test.runTest
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
@@ -33,6 +35,8 @@ import org.robolectric.RobolectricTestRunner
 @OptIn(ExperimentalCoroutinesApi::class)
 @RunWith(RobolectricTestRunner::class)
 public class PagerModelTest {
+    private val testDispatcher = StandardTestDispatcher()
+    private val testScope = TestScope(testDispatcher)
 
     private val scrollsFlow = MutableSharedFlow<PagerScrollEvent>()
 
@@ -41,7 +45,7 @@ public class PagerModelTest {
     private val mockEnv: ModelEnvironment = mockk(relaxed = true) {
         every { reporter } returns mockReporter
         every { actionsRunner } returns mockActionsRunner
-        every { modelScope } returns TestScope()
+        every { modelScope } returns testScope
     }
     private val mockView: PagerView = mockk(relaxed = true)
     private val mockViewListener: PagerModel.Listener = mockk(relaxed = true)
@@ -65,6 +69,8 @@ public class PagerModelTest {
 
         mockkStatic(PagerView::pagerScrolls)
         every { mockView.pagerScrolls() } returns scrollsFlow
+
+        testScope.runCurrent()
     }
 
     @Test
@@ -81,7 +87,10 @@ public class PagerModelTest {
         // Verify that the correct number of page items is available via the model
         assertEquals(3, pagerModel.items.size)
 
+        // Verify that the model notified the view to scroll to the first page
         verify { mockViewListener.scrollTo(0) }
+        // Verify that actions were run for the initial page display
+        verify(exactly = 1) { mockActionsRunner.run(any(), any()) }
     }
 
     @Test
@@ -105,10 +114,9 @@ public class PagerModelTest {
             assertTrue(updatedState.hasNext)
             assertTrue(updatedState.hasPrevious)
 
-            verify {
-                mockReporter.report(any(), any())
-                mockActionsRunner.run(any(), any())
-            }
+            // Verify that we reported an event and ran actions
+            verify { mockReporter.report(any(), any()) }
+            verify(exactly = 1) { mockActionsRunner.run(any(), any()) }
 
             ensureAllEventsConsumed()
         }
@@ -135,7 +143,7 @@ public class PagerModelTest {
             assertTrue(updatedState.hasNext)
             assertTrue(updatedState.hasPrevious)
 
-            // Verify that we didn't report an event, but ran any actions for the given page.
+            // Verify that we didn't report an event, but did run actions.
             verify(exactly = 0) { mockReporter.report(any(), any()) }
             verify(exactly = 1) { mockActionsRunner.run(any(), any()) }
 
@@ -148,14 +156,20 @@ public class PagerModelTest {
         pagerModel.onViewAttached(mockView)
 
         verify { mockViewListener.scrollTo(0) }
+        // Verify actions were run for the initial page display
+        verify(exactly = 1) { mockActionsRunner.run(any(), any()) }
 
         pagerState.update { it.copyWithPageIndex(1) }
+        // Run the pending state update task, so the model can process it.
+        testScope.runCurrent()
 
         val state = pagerState.changes.first()
         // Sanity check
         assertEquals(1, state.pageIndex)
 
         verify { mockViewListener.scrollTo(1) }
+        // Verify actions were also run on display of the next page
+        verify(exactly = 2) { mockActionsRunner.run(any(), any()) }
     }
 
     @Test