Refactor permissions requests to use ActivityResultContract (#4391)

The app currently uses a custom callback system for requesting
permissions, located in `BaseActivity`.
This code doesn't work when the activity gets re-created before the
permission is granted: the callback will be lost with the Activity and
no action will be performed after the permission is granted.

To avoid these issues while still simplifying the code, Google
recommends to use the ActivityResultContract APIs to request
permissions, which allow to register persistent callbacks. This pull
request removes the legacy API and replaces the calls with
`registerForActivityResult(ActivityResultContracts.RequestPermission())`.

- `ActivityResultContracts.RequestPermission` will check if the
permission is already granted and call the callback synchronously when
possible. So this check doesn't need to be performed anymore.
- In `SearchStatusesFragment` and `SFragment`, the download action to
launch after granting the permission requires an argument (a list of
media URLs). This argument is temporarily stored in a Fragment field and
saved and restored as part of the instance state, so the action can
properly resume after an Activity re-creation.

app/src/main/java/com/keylesspalace/tusky/fragment/SFragment.kt

@@ -21,17 +21,19 @@ import android.content.ClipboardManager
 import android.content.Context
 import android.content.DialogInterface
 import android.content.Intent
-import android.content.pm.PackageManager
 import android.net.Uri
 import android.os.Build
+import android.os.Bundle
 import android.os.Environment
 import android.util.Log
 import android.view.MenuItem
 import android.view.View
 import android.widget.Toast
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.appcompat.app.AlertDialog
 import androidx.appcompat.widget.PopupMenu
 import androidx.core.app.ActivityOptionsCompat
+import androidx.core.content.getSystemService
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.lifecycleScope
 import at.connyduck.calladapter.networkresult.fold
@@ -93,6 +95,22 @@ abstract class SFragment : Fragment(), Injectable {
     @Inject
     lateinit var instanceInfoRepository: InstanceInfoRepository
 
+    private var pendingMediaDownloads: List<String>? = null
+
+    private val downloadAllMediaPermissionLauncher =
+        registerForActivityResult(ActivityResultContracts.RequestPermission()) { isGranted ->
+            if (isGranted) {
+                pendingMediaDownloads?.let { downloadAllMedia(it) }
+            } else {
+                Toast.makeText(
+                    context,
+                    R.string.error_media_download_permission,
+                    Toast.LENGTH_SHORT
+                ).show()
+            }
+            pendingMediaDownloads = null
+        }
+
     override fun startActivity(intent: Intent) {
         requireActivity().startActivityWithSlideInAnimation(intent)
     }
@@ -106,6 +124,18 @@ abstract class SFragment : Fragment(), Injectable {
         }
     }
 
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        pendingMediaDownloads = savedInstanceState?.getStringArrayList(PENDING_MEDIA_DOWNLOADS_STATE_KEY)
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        pendingMediaDownloads?.let {
+            outState.putStringArrayList(PENDING_MEDIA_DOWNLOADS_STATE_KEY, ArrayList(it))
+        }
+    }
+
     override fun onResume() {
         super.onResume()
 
@@ -522,13 +552,11 @@ abstract class SFragment : Fragment(), Injectable {
         }
     }
 
-    private fun downloadAllMedia(status: Status) {
+    private fun downloadAllMedia(mediaUrls: List<String>) {
         Toast.makeText(context, R.string.downloading_media, Toast.LENGTH_SHORT).show()
-        val downloadManager = requireActivity().getSystemService(
-            Context.DOWNLOAD_SERVICE
-        ) as DownloadManager
+        val downloadManager: DownloadManager = requireContext().getSystemService()!!
 
-        for ((_, url) in status.attachments) {
+        for (url in mediaUrls) {
             val uri = Uri.parse(url)
             downloadManager.enqueue(
                 DownloadManager.Request(uri).apply {
@@ -542,26 +570,22 @@ abstract class SFragment : Fragment(), Injectable {
     }
 
     private fun requestDownloadAllMedia(status: Status) {
+        if (status.attachments.isEmpty()) {
+            return
+        }
+        val mediaUrls = status.attachments.map { it.url }
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) {
-            val permissions = arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE)
-            (activity as BaseActivity).requestPermissions(permissions) { _, grantResults ->
-                if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
-                    downloadAllMedia(status)
-                } else {
-                    Toast.makeText(
-                        context,
-                        R.string.error_media_download_permission,
-                        Toast.LENGTH_SHORT
-                    ).show()
-                }
-            }
+            pendingMediaDownloads = mediaUrls
+            downloadAllMediaPermissionLauncher.launch(Manifest.permission.WRITE_EXTERNAL_STORAGE)
         } else {
-            downloadAllMedia(status)
+            downloadAllMedia(mediaUrls)
         }
     }
 
     companion object {
         private const val TAG = "SFragment"
+        private const val PENDING_MEDIA_DOWNLOADS_STATE_KEY = "pending_media_downloads"
+
         private fun accountIsInMentions(
             account: AccountEntity?,
             mentions: List<Status.Mention>