详解如何获取C#类中发生数据变化的属性信息

// 自动属性声明
public class Entity1
{
  public Guid Id { get; set; }
}

// 完整的属性声明
public class Entity2
{
  private Guid _id;

  public Guid Id
  {
    get => _id;
    set => _id = value;
  }
}

public class Sample
{
  private string _a;

  public string A
  {
    get => _a;
    set
    {
      if (_a == value)
        return;

      string old = _a;
      _a = value;
      propertyChangelogs.Add(new PropertyChangelog<Sample>(nameof(A), old, _a));
    }
  }

  private double _b;

  public double B
  {
    get => _b;
    set
    {
      if (_b == value)
        return;

      double old = _b;
      _b = value;
      propertyChangelogs.Add(new PropertyChangelog<Sample>(nameof(B), old.ToString(), _b.ToString()));
    }
  }

  private IList<PropertyChangelog<Sample>> propertyChangelogs = new List<PropertyChangelog<Sample>>();

  public IEnumerable<PropertyChangelog<Sample>> Changelogs() => propertyChangelogs;
}

public class PropertyChangelog<T>
{
  /// <summary>
  /// ctor
  /// </summary>
  public PropertyChangelog()
  { }

  /// <summary>
  /// ctor
  /// </summary>
  /// <param name="propertyName">属性名称</param>
  /// <param name="oldValue">旧值</param>
  /// <param name="newValue">新值</param>
  public PropertyChangelog(string propertyName, string oldValue, string newValue)
  {
    PropertyName = propertyName;
    OldValue = oldValue;
    NewValue = newValue;
  }

  /// <summary>
  /// ctor
  /// </summary>
  /// <param name="className">类名</param>
  /// <param name="propertyName">属性名称</param>
  /// <param name="oldValue">旧值</param>
  /// <param name="newValue">新值</param>
  /// <param name="changedTime">修改时间</param>
  public PropertyChangelog(string className, string propertyName, string oldValue, string newValue, DateTime changedTime)
    : this(propertyName, oldValue, newValue)
  {
    ClassName = className;
    ChangedTime = changedTime;
  }

  /// <summary>
  /// 类名称
  /// </summary>
  public string ClassName { get; set; } = typeof(T).FullName;

  /// <summary>
  /// 属性名称
  /// </summary>
  public string PropertyName { get; set; }

  /// <summary>
  /// 旧值
  /// </summary>
  public string OldValue { get; set; }

  /// <summary>
  /// 新值
  /// </summary>
  public string NewValue { get; set; }

  /// <summary>
  /// 修改时间
  /// </summary>
  public DateTime ChangedTime { get; set; } = DateTime.Now;
}

/// <summary>
/// 为指定的属性设定数据变更记录
/// </summary>
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Property)]
public class PropertyChangeTrackingAttribute : Attribute
{
  /// <summary>
  /// 指定 PropertyChangeTrackingAttribute 属性的默认值
  /// </summary>
  public static readonly PropertyChangeTrackingAttribute Default = new PropertyChangeTrackingAttribute();

  /// <summary>
  /// 构造一个新的 PropertyChangeTrackingAttribute 特性实例
  /// </summary>
  public PropertyChangeTrackingAttribute()
  { }

  /// <summary>
  /// 构造一个新的 PropertyChangeTrackingAttribute 特性实例
  /// </summary>
  /// <param name="ignore">是否忽略该字段的数据变化</param>
  public PropertyChangeTrackingAttribute(bool ignore = false)
  {
    IgnoreValue = ignore;
  }

  /// <summary>
  /// 构造一个新的 PropertyChangeTrackingAttribute 特性实例
  /// </summary>
  /// <param name="displayName">属性对应页面显示名称</param>
  public PropertyChangeTrackingAttribute(string displayName)
    : this(false)
    {
      DisplayNameValue = displayName;
    }

  /// <summary>
  /// 构造一个新的 PropertyChangeTrackingAttribute 特性实例
  /// </summary>
  /// <param name="displayName">属性对应页面显示名称</param>
  /// <param name="ignore">是否忽略该字段的数据变化</param>
  public PropertyChangeTrackingAttribute(string displayName, bool ignore)
    : this(ignore)
    {
      DisplayNameValue = displayName;
    }

  /// <summary>
  /// 获取特性中的属性对应页面上显示名称参数信息
  /// </summary>
  public virtual string DisplayName => DisplayNameValue;

  /// <summary>
  /// 获取特性中的是否忽略该字段的数据变化参数信息
  /// </summary>
  public virtual bool Ignore => IgnoreValue;

  /// <summary>
  /// 修改属性对应页面显示名称参数值
  /// </summary>
  protected string DisplayNameValue { get; set; }

  /// <summary>
  /// 修改是否忽略该字段的数据变化
  /// </summary>
  protected bool IgnoreValue { get; set; }
}

/// <summary>
/// 获取类属性数据变化记录
/// </summary>
/// <typeparam name="T">监听的类类型</typeparam>
/// <param name="oldObj">包含原始值的类</param>
/// <param name="newObj">变更属性值后的类</param>
/// <param name="propertyName">指定的属性名称</param>
/// <returns></returns>
public static IEnumerable<PropertyChangelog<T>> GetPropertyLogs<T>(this T oldObj, T newObj, string propertyName = null)
{
  IList<PropertyChangelog<T>> changelogs = new List<PropertyChangelog<T>>();

  // 1、获取需要添加数据变更记录的属性信息
  //
  IList<PropertyInfo> properties = new List<PropertyInfo>();

  // PropertyChangeTracking 特性的类型
  var attributeType = typeof(PropertyChangeTrackingAttribute);

  // 对应的类中包含的属性信息
  var classProperties = typeof(T).GetProperties();

  // 获取类中需要添加变更记录的属性信息
  //
  bool flag = Attribute.IsDefined(typeof(T), attributeType);

  foreach (var i in classProperties)
  {
    // 获取当前属性添加的特性信息
    var attributeInfo = (PropertyChangeTrackingAttribute)i.GetCustomAttribute(attributeType);

    // 类未添加特性，并且该属性也未添加特性
    if (!flag && attributeInfo == null)
      continue;

    // 类添加特性，该属性未添加特性
    if (flag && attributeInfo == null)
      properties.Add(i);

    // 不管类有没有添加特性，只要类中的属性添加特性，并且 Ignore 为 false
    if (attributeInfo != null && !attributeInfo.Ignore)
      properties.Add(i);
  }

  // 2、判断指定的属性数据是否发生变更
  //
  foreach (var property in properties)
  {
    var oldValue = property.GetValue(oldObj) ?? "";
    var newValue = property.GetValue(newObj) ?? "";

    if (oldValue.Equals(newValue))
      continue;

    // 获取当前属性在页面上显示的名称
    //
    var attributeInfo = (PropertyChangeTrackingAttribute)property.GetCustomAttribute(attributeType);
    string displayName = attributeInfo == null ? property.Name
      : attributeInfo.DisplayName;

    changelogs.Add(new PropertyChangelog<T>(property.Name, displayName, oldValue.ToString(), newValue.ToString()));
  }

  return string.IsNullOrEmpty(propertyName) ? changelogs
    : changelogs.Where(i => i.PropertyName.Equals(propertyName));
}

[PropertyChangeTracking]
public class Entity
{
  [PropertyChangeTracking(ignore: true)]
  public Guid Id { get; set; }

  [PropertyChangeTracking(displayName: "序号")]
  public string OId { get; set; }

  [PropertyChangeTracking(displayName: "第一个字段")]
  public string A { get; set; }

  public double B { get; set; }

  public bool C { get; set; }

  public DateTime Date { get; set; } = DateTime.Now;
}