[GH] Don't drop retry/refresh events before uiReceiver is set

evant · copybara-github · commit 5675330a0b06 · 2025-01-28T09:50:01.000-08:00
## Proposed Changes Because uiReceiver is set asynchronously it's possible to race with a call to retry or refresh on the PagingDataPresenter. Changed the implementation to record calling these methods and then forward the event when the uiReceiver is set. ## Testing Test: ./gradlew test connectedCheck ## Issues Fixed Fixes: b/330725007 This is an imported pull request from #754. Resolves #754 Github-Pr-Head-Sha: b2603e5 GitOrigin-RevId: 6cf6538 Change-Id: I46f7b0538108a070ca417f44113d723610b541ba
diff --git a/paging/paging-common/src/commonMain/kotlin/androidx/paging/PagingDataPresenter.kt b/paging/paging-common/src/commonMain/kotlin/androidx/paging/PagingDataPresenter.kt
@@ -68,7 +68,7 @@ public abstract class PagingDataPresenter<T : Any>(
     cachedPagingData: PagingData<T>? = null,
 ) {
     private var hintReceiver: HintReceiver? = null
-    private var uiReceiver: UiReceiver? = null
+    private var uiReceiver: UiReceiver = InitialUiReceiver()
     private var pageStore: PageStore<T> = PageStore.initial(cachedPagingData?.cachedEvent())
     private val combinedLoadStatesCollection =
         MutableCombinedLoadStateCollection().apply {
@@ -114,7 +114,7 @@ public abstract class PagingDataPresenter<T : Any>(
 
     public suspend fun collectFrom(pagingData: PagingData<T>): @JvmSuppressWildcards Unit {
         collectFromRunner.runInIsolation {
-            uiReceiver = pagingData.uiReceiver
+            setUiReceiver(pagingData.uiReceiver)
             pagingData.flow.collect { event ->
                 log(VERBOSE) { "Collected $event" }
                 withContext(mainContext) {
@@ -309,7 +309,7 @@ public abstract class PagingDataPresenter<T : Any>(
      */
     public fun retry() {
         log(DEBUG) { "Retry signal received" }
-        uiReceiver?.retry()
+        uiReceiver.retry()
     }
 
     /**
@@ -329,7 +329,7 @@ public abstract class PagingDataPresenter<T : Any>(
      */
     public fun refresh() {
         log(DEBUG) { "Refresh signal received" }
-        uiReceiver?.refresh()
+        uiReceiver.refresh()
     }
 
     /** @return Total number of presented items, including placeholders. */
@@ -500,6 +500,33 @@ public abstract class PagingDataPresenter<T : Any>(
             hintReceiver?.accessHint(newPageStore.initializeHint())
         }
     }
+
+    // Holds on to retry/refresh requests to deliver them when the real UiReceiver is attached.
+    private class InitialUiReceiver : UiReceiver {
+        var retry = false
+        var refresh = false
+
+        override fun retry() {
+            retry = true
+        }
+
+        override fun refresh() {
+            refresh = true
+        }
+    }
+
+    private fun setUiReceiver(receiver: UiReceiver) {
+        val oldReceiver = this.uiReceiver
+        this.uiReceiver = receiver
+        if (oldReceiver is InitialUiReceiver) {
+            if (oldReceiver.retry) {
+                receiver.retry()
+            }
+            if (oldReceiver.refresh) {
+                receiver.refresh()
+            }
+        }
+    }
 }
 
 /**
diff --git a/paging/paging-common/src/commonTest/kotlin/androidx/paging/PagingDataPresenterTest.kt b/paging/paging-common/src/commonTest/kotlin/androidx/paging/PagingDataPresenterTest.kt
@@ -138,6 +138,36 @@ class PagingDataPresenterTest {
             job.cancel()
         }
 
+    @Test
+    fun retrySentBeforeCollection() =
+        testScope.run {
+            val presenter = SimplePresenter()
+            val receiver = UiReceiverFake()
+
+            presenter.retry()
+
+            val job = launch { presenter.collectFrom(infinitelySuspendingPagingData(receiver)) }
+
+            assertEquals(1, receiver.retryEvents.size)
+
+            job.cancel()
+        }
+
+    @Test
+    fun refreshSentBeforeCollection() =
+        testScope.runTest {
+            val presenter = SimplePresenter()
+            val receiver = UiReceiverFake()
+
+            presenter.refresh()
+
+            val job = launch { presenter.collectFrom(infinitelySuspendingPagingData(receiver)) }
+
+            assertEquals(1, receiver.refreshEvents.size)
+
+            job.cancel()
+        }
+
     @Test
     fun uiReceiverSetImmediately() =
         testScope.runTest {
@@ -2471,7 +2501,6 @@ class PagingDataPresenterTest {
             val job1 = launch {
                 presenter.collectFrom(PagingData(flow, uiReceiver2, dummyHintReceiver))
             }
-            presenter.refresh()
             assertThat(uiReceiver.refreshEvents).hasSize(0)
             assertThat(uiReceiver2.refreshEvents).hasSize(1)
             job1.cancel()
