Fix onBackPressed() deprecation in SharedDecksActivity

Moved the previous back handling code from the activity to the related
fragment. The predictive BACK navigation is done by changing the enabled
status of the back callback every time isDownloadInProgress is updated.

There was also a direct call to the activity onBackPressed() which was
replaced by the equivalent onBackPressedDispatcher.onBackPressed().

AnkiDroid/src/main/java/com/ichi2/anki/SharedDecksActivity.kt

@@ -240,44 +240,6 @@ class SharedDecksActivity : AnkiActivity() {
         onBackPressedDispatcher.addCallback(onBackPressedCallback)
     }
 
-    /**
-     * If download screen is open:
-     *      If download is in progress: Show download cancellation dialog
-     *      If download is not in progress: Close the download screen
-     * Otherwise, close the WebView.
-     */
-    @Deprecated("Deprecated in Java")
-    @Suppress("deprecation") // onBackPressed
-    override fun onBackPressed() {
-        when {
-            sharedDecksDownloadFragmentExists() -> {
-                supportFragmentManager.findFragmentByTag(SHARED_DECKS_DOWNLOAD_FRAGMENT)?.let {
-                    if ((it as SharedDecksDownloadFragment).isDownloadInProgress) {
-                        Timber.i("Back pressed when download is in progress, show cancellation confirmation dialog")
-                        // Show cancel confirmation dialog if download is in progress
-                        it.showCancelConfirmationDialog()
-                    } else {
-                        Timber.i("Back pressed when download is not in progress but download screen is open, close fragment")
-                        // Remove fragment
-                        supportFragmentManager.commit {
-                            remove(it)
-                        }
-                    }
-                }
-                supportFragmentManager.popBackStackImmediate()
-            }
-            else -> {
-                Timber.i("Back pressed which would lead to closing of the WebView")
-                super.onBackPressed()
-            }
-        }
-    }
-
-    private fun sharedDecksDownloadFragmentExists(): Boolean {
-        val sharedDecksDownloadFragment = supportFragmentManager.findFragmentByTag(SHARED_DECKS_DOWNLOAD_FRAGMENT)
-        return sharedDecksDownloadFragment != null && sharedDecksDownloadFragment.isAdded
-    }
-
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.download_shared_decks_menu, menu)
 

AnkiDroid/src/main/java/com/ichi2/anki/SharedDecksDownloadFragment.kt

@@ -33,6 +33,7 @@ import android.webkit.CookieManager
 import android.widget.Button
 import android.widget.ProgressBar
 import android.widget.TextView
+import androidx.activity.OnBackPressedCallback
 import androidx.appcompat.app.AlertDialog
 import androidx.core.content.ContextCompat
 import androidx.core.content.FileProvider
@@ -83,6 +84,11 @@ class SharedDecksDownloadFragment : Fragment(R.layout.fragment_shared_decks_down
     var isDownloadInProgress = false
 
     private var downloadCancelConfirmationDialog: AlertDialog? = null
+    private val onBackPressedCallback = object : OnBackPressedCallback(isDownloadInProgress) {
+        override fun handleOnBackPressed() {
+            showCancelConfirmationDialog()
+        }
+    }
 
     companion object {
         const val DOWNLOAD_PROGRESS_CHECK_DELAY = 1000L
@@ -134,6 +140,7 @@ class SharedDecksDownloadFragment : Fragment(R.layout.fragment_shared_decks_down
             cancelButton.visibility = View.VISIBLE
             tryAgainButton.visibility = View.GONE
         }
+        requireActivity().onBackPressedDispatcher.addCallback(onBackPressedCallback)
     }
 
     /**
@@ -170,6 +177,7 @@ class SharedDecksDownloadFragment : Fragment(R.layout.fragment_shared_decks_down
         downloadId = downloadManager.enqueue(downloadRequest)
         fileName = currentFileName
         isDownloadInProgress = true
+        onBackPressedCallback.isEnabled = isDownloadInProgress
         Timber.d("Download ID -> $downloadId")
         Timber.d("File name -> $fileName")
         view?.findViewById<TextView>(R.id.downloading_title)?.text = getString(R.string.downloading_file, fileName)
@@ -473,20 +481,21 @@ class SharedDecksDownloadFragment : Fragment(R.layout.fragment_shared_decks_down
 
         unregisterReceiver()
         isDownloadInProgress = false
+        onBackPressedCallback.isEnabled = isDownloadInProgress
 
         // If the cancel confirmation dialog is being shown and the download is no longer in progress, then remove the dialog.
         removeCancelConfirmationDialog()
     }
 
-    @Suppress("deprecation") // onBackPressed
-    fun showCancelConfirmationDialog() {
+    private fun showCancelConfirmationDialog() {
         downloadCancelConfirmationDialog = AlertDialog.Builder(requireContext()).create {
             setTitle(R.string.cancel_download_question_title)
             setPositiveButton(R.string.dialog_yes) { _, _ ->
                 downloadManager.remove(downloadId)
                 unregisterReceiver()
                 isDownloadInProgress = false
-                activity?.onBackPressed()
+                onBackPressedCallback.isEnabled = isDownloadInProgress
+                activity?.onBackPressedDispatcher?.onBackPressed()
             }
             setNegativeButton(R.string.dialog_no) { _, _ ->
                 downloadCancelConfirmationDialog?.dismiss()