415 lines
10 KiB
Markdown
415 lines
10 KiB
Markdown
# Performance Optimization
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本节定义性能优化策略和最佳实践，确保控件库满足 NFR 性能要求。
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---
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### Performance Targets (from NFR)
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| 指标 | 目标值 | 测量方法 |
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|------|--------|----------|
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| UI 渲染帧率 | 60fps (16ms/frame) | Visual Studio Performance Profiler |
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| 主题切换时间 | < 100ms | Stopwatch 测量 |
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| PropertyGrid 生成（50 属性） | < 200ms | Stopwatch 测量 |
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| 应用启动时间 | < 2s | 从启动到窗口显示 |
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| 内存占用 | < 100MB (空闲时) | Task Manager / dotnet-counters |
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---
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### UI Rendering Performance
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**关键原则：避免在 UI 线程执行耗时操作**
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**❌ 反面示例 - 阻塞 UI 线程：**
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```csharp
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// 错误：在属性 getter 中执行反射
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public ObservableCollection<PropertyItem> Properties
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{
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get
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{
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var items = new ObservableCollection<PropertyItem>();
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if (SelectedObject != null)
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{
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// 耗时操作会阻塞 UI 渲染
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var properties = SelectedObject.GetType().GetProperties();
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foreach (var prop in properties)
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{
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items.Add(CreatePropertyItem(SelectedObject, prop));
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}
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}
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return items;
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}
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}
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```
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**✅ 正确示例 - 异步加载：**
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```csharp
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private ObservableCollection<PropertyItem> _properties = new();
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public ObservableCollection<PropertyItem> Properties => _properties;
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private async void RefreshProperties(object? obj)
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{
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_properties.Clear();
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if (obj == null) return;
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// 在后台线程执行反射
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var items = await Task.Run(() =>
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{
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var result = new List<PropertyItem>();
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var properties = obj.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance);
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foreach (var prop in properties)
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{
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result.Add(CreatePropertyItem(obj, prop));
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}
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return result;
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});
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// 回到 UI 线程更新集合
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foreach (var item in items)
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{
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_properties.Add(item);
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}
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}
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```
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---
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### Reflection Optimization
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**问题：反射是 PropertyGrid 的性能瓶颈**
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**优化策略 1：缓存 PropertyInfo**
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```csharp
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private static readonly ConcurrentDictionary<Type, PropertyInfo[]> _propertyCache = new();
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private PropertyInfo[] GetCachedProperties(Type type)
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{
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return _propertyCache.GetOrAdd(type, t =>
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t.GetProperties(BindingFlags.Public | BindingFlags.Instance)
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);
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}
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```
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**优化策略 2：缓存 Attribute 读取**
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```csharp
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private static readonly ConcurrentDictionary<PropertyInfo, CategoryAttribute?> _categoryCache = new();
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private string? GetCategory(PropertyInfo prop)
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{
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var attr = _categoryCache.GetOrAdd(prop, p =>
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p.GetCustomAttribute<CategoryAttribute>()
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);
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return attr?.Category;
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}
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```
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**优化策略 3：使用编译表达式替代反射调用（可选）**
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```csharp
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// 反射调用（慢）
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var value = propertyInfo.GetValue(obj);
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// 编译表达式（快 10-100 倍）
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private static Func<object, object> CreateGetter(PropertyInfo prop)
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{
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var instance = Expression.Parameter(typeof(object), "instance");
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var convert = Expression.Convert(instance, prop.DeclaringType!);
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var property = Expression.Property(convert, prop);
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var convertResult = Expression.Convert(property, typeof(object));
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return Expression.Lambda<Func<object, object>>(convertResult, instance).Compile();
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}
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```
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**性能对比：**
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```
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反射 GetValue: ~1000 ns/调用
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编译表达式: ~10 ns/调用
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直接属性访问: ~1 ns/调用
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```
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---
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### Theme Switching Performance
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**优化主题切换速度（目标 < 100ms）：**
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**❌ 反面示例 - 逐个替换资源：**
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```csharp
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// 错误：逐个替换资源会触发多次 UI 刷新
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foreach (var key in themeColors.Keys)
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{
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Application.Current.Resources[key] = themeColors[key];
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}
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```
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**✅ 正确示例 - 批量替换 ResourceDictionary：**
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```csharp
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public static void ApplyTheme(ThemeType type)
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{
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var app = Application.Current;
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if (app == null) return;
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// 移除旧主题
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var oldTheme = app.Resources.MergedDictionaries
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.FirstOrDefault(d => d.Source?.ToString().Contains("Theme") == true);
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if (oldTheme != null)
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app.Resources.MergedDictionaries.Remove(oldTheme);
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// 一次性加载新主题（单次 UI 刷新）
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var uri = type == ThemeType.Light
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? new Uri("avares://Penguin.AvaloniaUI/Themes/LightTheme.axaml")
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: new Uri("avares://Penguin.AvaloniaUI/Themes/DarkTheme.axaml");
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var newTheme = new ResourceDictionary { Source = uri };
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app.Resources.MergedDictionaries.Add(newTheme);
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_currentTheme = type;
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ThemeChanged?.Invoke(null, type);
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}
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```
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**预加载主题资源（可选优化）：**
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```csharp
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private static ResourceDictionary? _cachedLightTheme;
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private static ResourceDictionary? _cachedDarkTheme;
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static ThemeManager()
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{
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// 应用启动时预加载主题
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_cachedLightTheme = LoadThemeResource(ThemeType.Light);
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_cachedDarkTheme = LoadThemeResource(ThemeType.Dark);
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}
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public static void ApplyTheme(ThemeType type)
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{
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var theme = type == ThemeType.Light ? _cachedLightTheme : _cachedDarkTheme;
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// 直接使用缓存的主题，无需重新加载
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}
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```
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---
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### Memory Management
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**避免内存泄漏的常见陷阱：**
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**问题 1：事件订阅未取消**
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```csharp
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// ❌ 可能导致内存泄漏
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public class PropertyGrid : TemplatedControl
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{
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public PropertyGrid()
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{
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ThemeManager.ThemeChanged += OnThemeChanged;
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// 没有取消订阅！
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}
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private void OnThemeChanged(object? sender, ThemeType type)
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{
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RefreshTheme();
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}
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}
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// ✅ 正确实现 IDisposable
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public class PropertyGrid : TemplatedControl, IDisposable
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{
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public PropertyGrid()
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{
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ThemeManager.ThemeChanged += OnThemeChanged;
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}
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public void Dispose()
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{
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ThemeManager.ThemeChanged -= OnThemeChanged;
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}
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private void OnThemeChanged(object? sender, ThemeType type)
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{
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RefreshTheme();
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}
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}
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```
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**问题 2：ObservableCollection 过度使用**
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```csharp
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// ❌ 每次都创建新集合
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public ObservableCollection<PropertyItem> Properties
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{
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get => new ObservableCollection<PropertyItem>(GetProperties());
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}
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// ✅ 复用同一个集合
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private ObservableCollection<PropertyItem> _properties = new();
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public ObservableCollection<PropertyItem> Properties => _properties;
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private void RefreshProperties()
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{
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_properties.Clear();
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foreach (var item in GetProperties())
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{
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_properties.Add(item);
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}
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}
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```
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---
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### Virtualization (Post-MVP)
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**如果 PropertyGrid 需要支持数百个属性，使用虚拟化：**
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```xml
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<ItemsControl Items="{Binding Properties}">
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<ItemsControl.ItemsPanel>
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<ItemsPanelTemplate>
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<!-- VirtualizingStackPanel 仅渲染可见项 -->
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<VirtualizingStackPanel />
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</ItemsPanelTemplate>
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</ItemsControl.ItemsPanel>
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</ItemsControl>
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```
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**虚拟化性能对比：**
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```
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100 个属性（非虚拟化）: ~300ms 生成 + 50MB 内存
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100 个属性（虚拟化）: ~100ms 生成 + 10MB 内存
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```
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---
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### Avoid Common Pitfalls
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**陷阱 1：在循环中触发属性变化通知**
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```csharp
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// ❌ 每次循环触发 UI 刷新
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for (int i = 0; i < 1000; i++)
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{
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Properties.Add(new PropertyItem()); // 触发 CollectionChanged
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}
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// ✅ 批量添加后触发一次刷新
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var items = new List<PropertyItem>();
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for (int i = 0; i < 1000; i++)
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{
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items.Add(new PropertyItem());
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}
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Properties.Clear();
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foreach (var item in items)
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{
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Properties.Add(item);
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}
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```
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**陷阱 2：频繁的字符串拼接**
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```csharp
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// ❌ 每次拼接创建新字符串
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string result = "";
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for (int i = 0; i < 100; i++)
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{
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result += properties[i].Name + ", ";
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}
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// ✅ 使用 StringBuilder
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var sb = new StringBuilder();
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for (int i = 0; i < 100; i++)
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{
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sb.Append(properties[i].Name).Append(", ");
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}
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var result = sb.ToString();
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```
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**陷阱 3：XAML 中的复杂绑定**
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```xml
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<!-- ❌ 每次渲染都执行转换 -->
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<TextBlock Text="{Binding PropertyType, Converter={StaticResource ComplexConverter}}" />
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<!-- ✅ 在 ViewModel 中预计算 -->
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<TextBlock Text="{Binding PropertyTypeDisplayName}" />
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```
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---
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### Performance Measurement
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**使用 Stopwatch 测量关键操作：**
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```csharp
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#if DEBUG
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private void RefreshProperties(object? obj)
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{
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var sw = Stopwatch.StartNew();
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// 核心逻辑
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_properties.Clear();
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var items = GetProperties(obj);
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foreach (var item in items)
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{
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_properties.Add(item);
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}
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sw.Stop();
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Debug.WriteLine($"[PropertyGrid] RefreshProperties took {sw.ElapsedMilliseconds}ms for {items.Count} properties");
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}
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#endif
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```
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**Visual Studio Performance Profiler：**
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1. 调试 → 性能探查器
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2. 选择"CPU 使用情况"或".NET 对象分配跟踪"
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3. 启动分析
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4. 执行性能关键操作（如生成 50 个属性）
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5. 停止分析并查看热点代码
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**dotnet-counters 监控内存：**
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```bash
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# 安装工具
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dotnet tool install --global dotnet-counters
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# 监控运行中的应用
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dotnet-counters monitor --process-id <pid> --counters System.Runtime
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```
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---
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### Optimization Checklist
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**开发时检查清单：**
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- [ ] 反射操作已缓存（PropertyInfo、Attribute）
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- [ ] 耗时操作（> 50ms）在后台线程执行
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- [ ] 事件订阅在控件销毁时取消
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- [ ] ObservableCollection 复用而非重建
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- [ ] 批量更新集合，避免频繁触发 CollectionChanged
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- [ ] 字符串拼接使用 StringBuilder
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- [ ] XAML 绑定避免复杂转换器
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- [ ] 主题切换批量替换 ResourceDictionary
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**发布前性能测试：**
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- [ ] PropertyGrid 50 属性生成 < 200ms
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- [ ] 主题切换 < 100ms
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- [ ] 应用启动 < 2s
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- [ ] 空闲时内存 < 100MB
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- [ ] 无明显的 UI 卡顿（帧率 > 50fps）
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---
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