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lib/pages/epub_reader/mixins/page_navigation_mixin.dart

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+part of '../reader_screen.dart';
+
+mixin _PageNavigationMixin on State<ReaderScreen> {
+  // === Borrowed state (provided by _ReaderScreenState fields) ===
+  int get currentPageInChapter;
+  set currentPageInChapter(int v);
+
+  int get totalPagesInChapter;
+  set totalPagesInChapter(int v);
+
+  int get currentSpineItemIndex;
+
+  BookSession get bookSession;
+
+  ReaderRendererController get rendererController;
+
+  // === Cross-mixin: _SpineNavigationMixin ===
+  Future<void> nextSpineItem();
+  Future<void> previousSpineItem();
+
+  // === Cross-mixin: _ProgressMixin ===
+  void updateProgressDebounced();
+  void saveProgress();
+
+  // === Cross-mixin: _ThemeMixin ===
+  EpubTheme getEpubTheme();
+
+  bool canPerformPageTurn(bool isNext) {
+    if (isNext) {
+      if (currentPageInChapter >= totalPagesInChapter - 1 &&
+          currentSpineItemIndex >= bookSession.spine.length - 1) {
+        _showToast('已经是最后一页');
+        return false;
+      }
+    } else {
+      if (currentPageInChapter <= 0 && currentSpineItemIndex <= 0) {
+        _showToast('已经是第一页');
+        return false;
+      }
+    }
+    return true;
+  }
+
+  Future<void> handlePageTurn(bool isNext) async {
+    if (isNext) {
+      await nextPage();
+    } else {
+      await previousPage();
+    }
+  }
+
+  Future<void> goToPage(int pageIndex) async {
+    if (pageIndex < 0 || pageIndex >= totalPagesInChapter) return;
+
+    setState(() {
+      currentPageInChapter = pageIndex;
+    });
+    updateProgressDebounced();
+
+    await rendererController.jumpToPage(pageIndex);
+    saveProgress();
+  }
+
+  Future<void> nextPage() async {
+    if (currentPageInChapter < totalPagesInChapter - 1) {
+      await goToPage(currentPageInChapter + 1);
+    } else {
+      await nextSpineItem();
+    }
+    saveProgress();
+  }
+
+  Future<void> previousPage() async {
+    if (currentPageInChapter > 0) {
+      await goToPage(currentPageInChapter - 1);
+    } else {
+      await previousSpineItem();
+    }
+    saveProgress();
+  }
+
+  void _showToast(String message) {
+    if (!mounted) return;
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(content: Text(message), duration: const Duration(seconds: 1)),
+    );
+  }
+}