整体调整了功能

FATrace.WPLApp/ViewModels/HelpManualViewModel.cs

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+using FATrace.WPLApp.Core;
+using FATrace.WPLApp.Services;
+using Prism.Commands;
+using System;
+using System.Collections.ObjectModel;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using System.Windows;
+
+namespace FATrace.WPLApp.ViewModels
+{
+    /// <summary>
+    /// 使用手册（PDF）查看页 VM
+    /// </summary>
+    public class HelpManualViewModel : NavigationViewModel
+    {
+        private readonly ILogService _log;
+
+        public HelpManualViewModel(ILogService log)
+        {
+            _log = log;
+
+            PdfFiles = new ObservableCollection<PdfFileItem>();
+            RefreshCommand = new DelegateCommand(async () => await LoadReportPdfsAsync(), () => !IsBusy)
+                .ObservesProperty(() => IsBusy);
+        }
+
+        private bool _isBusy;
+        /// <summary>
+        /// 是否忙碌（用于提示与禁用按钮）
+        /// </summary>
+        public bool IsBusy
+        {
+            get => _isBusy;
+            set { _isBusy = value; RaisePropertyChanged(); }
+        }
+
+        private string? _statusText;
+        /// <summary>
+        /// 页面状态文本（例如：未找到PDF）
+        /// </summary>
+        public string? StatusText
+        {
+            get => _statusText;
+            set { _statusText = value; RaisePropertyChanged(); }
+        }
+
+        /// <summary>
+        /// Report 目录下的 PDF 文件列表
+        /// </summary>
+        public ObservableCollection<PdfFileItem> PdfFiles { get; }
+
+        private PdfFileItem? _selectedPdf;
+        /// <summary>
+        /// 当前选择的 PDF
+        /// </summary>
+        public PdfFileItem? SelectedPdf
+        {
+            get => _selectedPdf;
+            set
+            {
+                _selectedPdf = value;
+                RaisePropertyChanged();
+                PdfFilePath = _selectedPdf?.FullPath;
+            }
+        }
+
+        private string? _pdfFilePath;
+        /// <summary>
+        /// 当前打开的 PDF 文件路径（绑定到 Syncfusion PdfViewerControl.ItemSource）
+        /// </summary>
+        public string? PdfFilePath
+        {
+            get => _pdfFilePath;
+            set { _pdfFilePath = value; RaisePropertyChanged(); }
+        }
+
+        /// <summary>
+        /// 刷新/重新扫描 PDF 文件
+        /// </summary>
+        public DelegateCommand RefreshCommand { get; }
+
+        /// <summary>
+        /// 获取运行目录下 Report 文件夹绝对路径
+        /// </summary>
+        /// <returns>Report 文件夹绝对路径</returns>
+        private string GetReportFolder()
+        {
+            var baseDir = AppDomain.CurrentDomain.BaseDirectory;
+            var folder = Path.Combine(baseDir, "Report");
+            try
+            {
+                if (!Directory.Exists(folder))
+                {
+                    Directory.CreateDirectory(folder);
+                }
+            }
+            catch (Exception ex)
+            {
+                _log.Error($"HelpManual: 创建Report目录失败: {ex}");
+            }
+            return folder;
+        }
+
+        /// <summary>
+        /// 扫描 Report 目录并加载 PDF 列表（默认打开第一个）
+        /// </summary>
+        /// <returns>Task</returns>
+        private async Task LoadReportPdfsAsync()
+        {
+            if (IsBusy) return;
+            try
+            {
+                IsBusy = true;
+                StatusText = string.Empty;
+
+                var folder = GetReportFolder();
+                _log.Info($"HelpManual: 扫描PDF目录: {folder}");
+
+                var list = await Task.Run(() =>
+                {
+                    if (!Directory.Exists(folder))
+                        return Array.Empty<PdfFileItem>();
+
+                    var files = Directory.GetFiles(folder, "*.pdf", SearchOption.TopDirectoryOnly)
+                        .Select(p => new PdfFileItem(Path.GetFileName(p), p))
+                        .OrderByDescending(a => a.FileName)
+                        .ToArray();
+
+                    return files;
+                });
+
+                Application.Current.Dispatcher.Invoke(() =>
+                {
+                    PdfFiles.Clear();
+                    foreach (var f in list) PdfFiles.Add(f);
+
+                    if (PdfFiles.Count == 0)
+                    {
+                        SelectedPdf = null;
+                        PdfFilePath = null;
+                        StatusText = "未在程序目录下的 Report 文件夹找到 PDF 文件，请将手册PDF放入该目录后点击【刷新】。";
+                        return;
+                    }
+
+                    // 保持原选择（若仍存在），否则默认第一个
+                    var keep = SelectedPdf != null
+                        ? PdfFiles.FirstOrDefault(a => string.Equals(a.FullPath, SelectedPdf.FullPath, StringComparison.OrdinalIgnoreCase))
+                        : null;
+
+                    SelectedPdf = keep ?? PdfFiles[0];
+                });
+            }
+            catch (Exception ex)
+            {
+                _log.Error($"HelpManual: 扫描/加载PDF失败: {ex}");
+                StatusText = $"加载PDF失败: {ex.Message}";
+                MessageBox.Show($"加载PDF失败: {ex.Message}", "错误", MessageBoxButton.OK, MessageBoxImage.Error);
+            }
+            finally
+            {
+                IsBusy = false;
+            }
+        }
+
+        /// <summary>
+        /// 页面导航进入时自动加载
+        /// </summary>
+        /// <param name="navigationContext">导航上下文</param>
+        public override async void OnNavigatedTo(Prism.Regions.NavigationContext navigationContext)
+        {
+            await LoadReportPdfsAsync();
+        }
+
+        /// <summary>
+        /// PDF 文件下拉项
+        /// </summary>
+        public class PdfFileItem
+        {
+            /// <summary>
+            /// 构造
+            /// </summary>
+            /// <param name="fileName">文件名</param>
+            /// <param name="fullPath">完整路径</param>
+            public PdfFileItem(string fileName, string fullPath)
+            {
+                FileName = fileName;
+                FullPath = fullPath;
+            }
+
+            /// <summary>
+            /// 文件名
+            /// </summary>
+            public string FileName { get; }
+
+            /// <summary>
+            /// 完整路径
+            /// </summary>
+            public string FullPath { get; }
+
+            /// <summary>
+            /// 用于下拉显示
+            /// </summary>
+            /// <returns>文件名</returns>
+            public override string ToString() => FileName;
+        }
+    }
+}