UX improvements: keep user edits & do not reset cursor

app/src/main/java/org/schabi/newpipe/download/DownloadDialog.java

@@ -75,6 +75,7 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Locale;
 import java.util.Objects;
+import java.util.Optional;
 
 import icepick.Icepick;
 import icepick.State;
@@ -566,21 +567,36 @@ public class DownloadDialog extends DialogFragment
     }
 
     private void onItemSelectedSetFileName() {
-        final String fileName = FilenameUtils.createFilename(getContext(),
+        final String fileName = FilenameUtils.createFilename(getContext(), currentInfo.getName());
-                currentInfo.getName());
+        final String prevFileName = Optional.ofNullable(dialogBinding.fileName.getText())
+                .map(Object::toString)
+                .orElse("");
+
+        if (prevFileName.isEmpty()
+                || prevFileName.equals(fileName)
+                || prevFileName.startsWith(getString(R.string.caption_file_name, fileName, ""))) {
+            // only update the file name field if it was not edited by the user
+
             switch (dialogBinding.videoAudioGroup.getCheckedRadioButtonId()) {
                 case R.id.audio_button:
                 case R.id.video_button:
+                    if (!prevFileName.equals(fileName)) {
+                        // since the user might have switched between audio and video, the correct
+                        // text might already be in place, so avoid resetting the cursor position
                         dialogBinding.fileName.setText(fileName);
+                    }
                     break;
+
                 case R.id.subtitle_button:
                     final String setSubtitleLanguageCode = subtitleStreamsAdapter
                             .getItem(selectedSubtitleIndex).getLanguageTag();
+                    // this will reset the cursor position, which is bad UX, but it can't be avoided
                     dialogBinding.fileName.setText(getString(
                             R.string.caption_file_name, fileName, setSubtitleLanguageCode));
                     break;
             }
         }
+    }
 
     @Override
     public void onNothingSelected(final AdapterView<?> parent) {