Fix deleting from slideshow

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

@@ -24,7 +24,6 @@ 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 javax.inject.Inject
 
 /**
@@ -125,14 +124,11 @@ class RemoveFilesDialogFragment :
             }
 
             finishActionMode()
-            finishPreviewImageActivity()
         }
     }
 
     override fun onNeutral(callerTag: String?) = Unit
 
-    private fun finishPreviewImageActivity() = getTypedActivity(PreviewImageActivity::class.java)?.finish()
-
     private fun setActionMode(actionMode: ActionMode?) {
         this.actionMode = actionMode
     }

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

@@ -56,6 +56,7 @@ import edu.umd.cs.findbugs.annotations.SuppressFBWarnings
 import java.io.Serializable
 import javax.inject.Inject
 import kotlin.math.max
+import kotlin.math.min
 
 /**
  * Holds a swiping gallery where image files contained in an Nextcloud directory are shown.
@@ -216,6 +217,17 @@ class PreviewImageActivity :
         }
     }
 
+    private fun updateViewPagerAfterDeletionAndAdvanceForward() {
+        val deletePosition = viewPager?.currentItem ?: return
+        previewImagePagerAdapter?.let { adapter ->
+            val nextPosition = min(deletePosition, adapter.itemCount - 1)
+            viewPager?.setCurrentItem(nextPosition, true)
+            adapter.delete(deletePosition)
+            // Page needs to be reselected after the adapter has been updated. Otherwise, wrong title is shown
+            selectPage(nextPosition)
+        }
+    }
+
     private fun handleBackPress() {
         onBackPressedDispatcher.addCallback(object : OnBackPressedCallback(true) {
             override fun handleOnBackPressed() {
@@ -285,22 +297,16 @@ class PreviewImageActivity :
         super.onRemoteOperationFinish(operation, result)
 
         if (operation is RemoveFileOperation) {
-            val deletePosition = viewPager?.currentItem ?: return
-            val nextPosition = if (deletePosition > 0) deletePosition - 1 else 0
-
             previewImagePagerAdapter?.let {
                 if (it.itemCount <= 1) {
                     backToDisplayActivity()
                     return
                 }
             }
 
-            if (user.isPresent) {
-                initViewPager(user.get())
+            if (result.isSuccess) {
+                updateViewPagerAfterDeletionAndAdvanceForward()
             }
-
-            viewPager?.setCurrentItem(nextPosition, true)
-            previewImagePagerAdapter?.delete(deletePosition)
         } else if (operation is SynchronizeFileOperation) {
             onSynchronizeFileOperationFinish(result)
         }

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

@@ -205,4 +205,11 @@ class PreviewImagePagerAdapter : FragmentStateAdapter {
     override fun createFragment(position: Int): Fragment = getItem(position)
 
     override fun getItemCount(): Int = imageFiles.size
+
+    override fun getItemId(position: Int): Long {
+        // The item ID function is needed to detect whether the deletion of the current item needs a UI update
+        return imageFiles.getOrNull(position)?.fileId ?: position.toLong()
+    }
+
+    override fun containsItem(itemId: Long): Boolean = imageFiles.any { it.fileId == itemId }
 }