feat: page up down handler

frontend/app_flowy/packages/flowy_editor/lib/src/service/internal_key_event_handlers/default_key_event_handlers.dart

@@ -8,6 +8,7 @@ import 'package:flowy_editor/src/service/internal_key_event_handlers/slash_handl
 import 'package:flowy_editor/src/service/internal_key_event_handlers/update_text_style_by_command_x_handler.dart';
 import 'package:flowy_editor/src/service/internal_key_event_handlers/whitespace_handler.dart';
 import 'package:flowy_editor/src/service/internal_key_event_handlers/select_all_handler.dart';
+import 'package:flowy_editor/src/service/internal_key_event_handlers/page_up_down_handler.dart';
 import 'package:flowy_editor/src/service/keyboard_service.dart';
 
 List<FlowyKeyEventHandler> defaultKeyEventHandlers = [
@@ -21,4 +22,5 @@ List<FlowyKeyEventHandler> defaultKeyEventHandlers = [
   updateTextStyleByCommandXHandler,
   whiteSpaceHandler,
   selectAllHandler,
+  pageUpDownHandler,
 ];

frontend/app_flowy/packages/flowy_editor/lib/src/service/internal_key_event_handlers/page_up_down_handler.dart

@@ -0,0 +1,31 @@
+import 'package:flowy_editor/flowy_editor.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+double? getEditorHeight(EditorState editorState) {
+  final renderObj =
+      editorState.service.scrollServiceKey.currentContext?.findRenderObject();
+  if (renderObj is RenderBox) {
+    return renderObj.size.height;
+  }
+  return null;
+}
+
+FlowyKeyEventHandler pageUpDownHandler = (editorState, event) {
+  if (event.logicalKey == LogicalKeyboardKey.pageUp) {
+    final scrollHeight = getEditorHeight(editorState);
+    final scrollService = editorState.service.scrollService;
+    if (scrollHeight != null && scrollService != null) {
+      scrollService.scrollTo(scrollService.dy - scrollHeight);
+    }
+    return KeyEventResult.handled;
+  } else if (event.logicalKey == LogicalKeyboardKey.pageDown) {
+    final scrollHeight = getEditorHeight(editorState);
+    final scrollService = editorState.service.scrollService;
+    if (scrollHeight != null && scrollService != null) {
+      scrollService.scrollTo(scrollService.dy + scrollHeight);
+    }
+    return KeyEventResult.handled;
+  }
+  return KeyEventResult.ignored;
+};