fix(slideshow): Use EventBus to notify activities of file deletion

Reduces the coupling, using an already existing EventBus pattern.
During registration, we need to first check if it is already registered.
Otherwise, the app crashed directly at first start with the error

org.greenrobot.eventbus.EventBusException: Subscriber class
com.owncloud.android.ui.activity.FileDisplayActivity already registered to
event class com.owncloud.android.ui.events.FilesRefreshEvent

Signed-off-by: Philipp Hasper <vcs@hasper.info>

Author: PhilLab

app/src/main/java/com/owncloud/android/ui/activity/FileDisplayActivity.kt

@@ -1,6 +1,7 @@
 /*
  * Nextcloud - Android Client
  *
+ * SPDX-FileCopyrightText: 2026 Philipp Hasper <vcs@hasper.info>
  * SPDX-FileCopyrightText: 2025 Alper Ozturk <alper.ozturk@nextcloud.com>
  * SPDX-FileCopyrightText: 2023-2024 TSI-mc <surinder.kumar@t-systems.com>
  * SPDX-FileCopyrightText: 2023 Archontis E. Kostis <arxontisk02@gmail.com>
@@ -120,6 +121,7 @@ import com.owncloud.android.ui.dialog.SendShareDialog.SendShareDialogDownloader
 import com.owncloud.android.ui.dialog.SortingOrderDialogFragment.OnSortingOrderListener
 import com.owncloud.android.ui.dialog.StoragePermissionDialogFragment
 import com.owncloud.android.ui.dialog.TermsOfServiceDialog
+import com.owncloud.android.ui.events.FilesRefreshEvent
 import com.owncloud.android.ui.events.SearchEvent
 import com.owncloud.android.ui.events.SyncEventFinished
 import com.owncloud.android.ui.events.TokenPushEvent
@@ -1450,12 +1452,6 @@ class FileDisplayActivity :
     }
     // endregion
 
-    override fun onStop() {
-        Log_OC.v(TAG, "onStop()")
-        unregisterReceivers()
-        super.onStop()
-    }
-
     override fun onSortingOrderChosen(selection: FileSortOrder?) {
         val ocFileListFragment = this.listOfFilesFragment
         ocFileListFragment?.sortFiles(selection)
@@ -2779,6 +2775,11 @@ class FileDisplayActivity :
 
         registerReceivers()
 
+        // Register for the FilesRefreshEvent, only if not already registered
+        if (!EventBus.getDefault().isRegistered(this)) {
+            EventBus.getDefault().register(this)
+        }
+
         if (SettingsActivity.isBackPressed) {
             Log_OC.d(TAG, "User returned from settings activity, skipping reset content logic")
             return
@@ -2787,6 +2788,15 @@ class FileDisplayActivity :
         initFile()
     }
 
+    public override fun onStop() {
+        Log_OC.v(TAG, "onStop()")
+        if (EventBus.getDefault().isRegistered(this)) {
+            EventBus.getDefault().unregister(this)
+        }
+        unregisterReceivers()
+        super.onStop()
+    }
+
     private fun initFile() {
         val userOpt = user
         if (userOpt.isEmpty) {
@@ -3040,6 +3050,14 @@ class FileDisplayActivity :
         })
     }
 
+    // region EventBus
+    @Suppress("unused")
+    @Subscribe(threadMode = ThreadMode.MAIN)
+    fun onFilesRefreshNeeded(event: FilesRefreshEvent) {
+        refreshCurrentDirectory()
+    }
+    // endregion
+
     private fun handleEcosystemIntent(intent: Intent?) {
         ecosystemManager.receiveAccount(
             intent,

app/src/main/java/com/owncloud/android/ui/dialog/RemoveFilesDialogFragment.kt

@@ -1,6 +1,7 @@
 /*
  * Nextcloud - Android Client
  *
+ * SPDX-FileCopyrightText: 2026 Philipp Hasper <vcs@hasper.info>
  * SPDX-FileCopyrightText: 2023 Alper Ozturk <alper.ozturk@nextcloud.com>
  * SPDX-FileCopyrightText: 2018 Andy Scherzinger <info@andy-scherzinger.de>
  * SPDX-FileCopyrightText: 2018 Jessie Chatham Spencer <jessie@teainspace.com>
@@ -25,7 +26,8 @@ import com.owncloud.android.datamodel.OCFile
 import com.owncloud.android.ui.activity.FileActivity
 import com.owncloud.android.ui.activity.FileDisplayActivity
 import com.owncloud.android.ui.dialog.ConfirmationDialogFragment.ConfirmationDialogFragmentListener
-import com.owncloud.android.ui.preview.PreviewImageActivity
+import com.owncloud.android.ui.events.FilesRefreshEvent
+import org.greenrobot.eventbus.EventBus
 import javax.inject.Inject
 
 /**
@@ -100,7 +102,6 @@ class RemoveFilesDialogFragment :
 
         val fileActivity = getTypedActivity(FileActivity::class.java)
         val fda = getTypedActivity(FileDisplayActivity::class.java)
-        val pia = getTypedActivity(PreviewImageActivity::class.java)
         connectivityService.isNetworkAndServerAvailable { isAvailable ->
             if (isAvailable) {
                 fileActivity?.showLoadingDialog(fileActivity.getString(R.string.wait_a_moment))
@@ -114,8 +115,7 @@ class RemoveFilesDialogFragment :
                 }
 
                 if (offlineFiles.isNotEmpty()) {
-                    fda?.refreshCurrentDirectory()
-                    pia?.initViewPager()
+                    EventBus.getDefault().post(FilesRefreshEvent())
                 }
 
                 fileActivity?.dismissLoadingDialog()
@@ -127,9 +127,7 @@ class RemoveFilesDialogFragment :
                         fileDataStorageManager.addRemoveFileOfflineOperation(file)
                     }
                 }
-
-                fda?.refreshCurrentDirectory()
-                pia?.initViewPager()
+                EventBus.getDefault().post(FilesRefreshEvent())
             }
 
             finishActionMode()

app/src/main/java/com/owncloud/android/ui/events/FilesRefreshEvent.kt

@@ -0,0 +1,13 @@
+/*
+ * Nextcloud - Android Client
+ *
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+package com.owncloud.android.ui.events
+
+/**
+ * Event denoting the need to refresh the files displayed in the current view
+ */
+class FilesRefreshEvent

app/src/main/java/com/owncloud/android/ui/preview/PreviewImageActivity.kt

@@ -1,6 +1,7 @@
 /*
  * Nextcloud - Android Client
  *
+ * SPDX-FileCopyrightText: 2026 Philipp Hasper <vcs@hasper.info>
  * SPDX-FileCopyrightText: 2024 Alper Ozturk <alper.ozturk@nextcloud.com>
  * SPDX-License-Identifier: AGPL-3.0-or-later
  */
@@ -45,13 +46,17 @@ import com.owncloud.android.operations.RemoveFileOperation
 import com.owncloud.android.operations.SynchronizeFileOperation
 import com.owncloud.android.ui.activity.FileActivity
 import com.owncloud.android.ui.activity.FileDisplayActivity
+import com.owncloud.android.ui.events.FilesRefreshEvent
 import com.owncloud.android.ui.fragment.FileFragment
 import com.owncloud.android.ui.fragment.GalleryFragment
 import com.owncloud.android.ui.fragment.OCFileListFragment
 import com.owncloud.android.ui.preview.model.PreviewImageActivityState
 import com.owncloud.android.utils.DisplayUtils
 import com.owncloud.android.utils.MimeTypeUtil
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings
+import org.greenrobot.eventbus.EventBus
+import org.greenrobot.eventbus.Subscribe
+import org.greenrobot.eventbus.ThreadMode
 import java.io.Serializable
 import javax.inject.Inject
 import kotlin.math.max
@@ -213,6 +218,14 @@ class PreviewImageActivity :
         }
     }
 
+    // region EventBus
+    @Suppress("unused")
+    @Subscribe(threadMode = ThreadMode.MAIN)
+    fun onFilesRefreshNeeded(event: FilesRefreshEvent) {
+        initViewPager()
+    }
+    // endregion
+
     fun initViewPager() {
         if (user.isPresent) {
             initViewPager(user.get())
@@ -264,6 +277,12 @@ class PreviewImageActivity :
     public override fun onStart() {
         super.onStart()
         registerReceivers()
+
+        // Register for the FilesRefreshEvent, only if not already registered
+        if (!EventBus.getDefault().isRegistered(this)) {
+            EventBus.getDefault().register(this)
+        }
+
         val optionalUser = user
         if (optionalUser.isPresent) {
             var file: OCFile? = file ?: throw IllegalStateException("Instanced with a NULL OCFile")
@@ -404,6 +423,10 @@ class PreviewImageActivity :
             downloadFinishReceiver = null
         }
 
+        if (EventBus.getDefault().isRegistered(this)) {
+            EventBus.getDefault().unregister(this)
+        }
+
         super.onStop()
     }