觸發屬性更改事件的較短代碼

Question

我有一個包含數十個屬性的類，需要引發屬性更改事件，目前我的代碼看起來像

public class Ethernet : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string timeStamp;

    public string TimeStamp
    {
        get { return timeStamp; }
        set
        {
            timeStamp = value;

            if(PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("TimeStamp"));
        }
    }
}

在 C# 中是否有更短的方法來編寫這種代碼，我對每個屬性都做了過多的復制/粘貼操作，我覺得必須有更好的方法。

Answer 1

引用的代碼不是寫的線程安全的。 請參閱實現 INotifyPropertyChanged 的​​模式？ 為什么下面的代碼更好，以及在接受的回復中指向 Eric Lippert 博客的鏈接為什么故事沒有就此結束。

    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null) handler(this, new PropertyChangedEventArgs("TimeStamp"));

有關實際問題的答案，請參閱實現 INotifyPropertyChanged - 是否存在更好的方法？ 包括這個 C# 6.0 快捷方式。

    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("TimeStamp"));

Answer 2

看看這個答案： https : //stackoverflow.com/a/2339904/259769

我的代碼提供和擴展方法來替換大部分設置代碼，讓我們將代碼縮短為：

public class Ethernet : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string timeStamp;

    public string TimeStamp
    {
        get { return timeStamp; }
        set { this.NotifySetProperty(ref timeStamp, value, () => this.TimeStamp); }
    }
}

這段代碼的另一個明顯優點是它立即變成了針對屬性名稱的強類型。

Answer 3

在 MVVM 模式中，經常使用屬性更改 / ing，典型的基本解決方案如下：

  public class ViewModelBase : INotifyPropertyChanged
  {
     public event PropertyChangedEventHandler PropertyChanged;

     protected void FirePropertyChanged([CallerMemberName] string propertyName = null)
     {
        if (propertyName == null)
           throw new ArgumentNullException("propertyName");
        try
        {
           this.OnPropertyChanged(propertyName);
        }
        catch (Exception exception)
        {
           Trace.TraceError("{0}.OnPropertyChanged threw {1}: {2}", this.GetType().FullName, exception.GetType().FullName, exception);
        }
     }
     protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
     {
        var handler = PropertyChanged;
        if (handler != null)
        {
           handler(this, new PropertyChangedEventArgs(propertyName));
        }
     }
  }

 public class Ethernet : ViewModelBase
  {
     private DataTime timeStamp;

     public DateTime TimeStamp
     {
        get
        {
           return timeStamp;
        }
        set
        {
           timeStamp = value;
           FirePropertyChanged();
        }
     }
  }

Answer 4

我愛上了這門課：

[Serializable]
public class PropertyChangedBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual bool SetProperty<T>(T value, ref T field, Expression<Func<object>> property)
    {
        return SetProperty(value, ref field, GetPropertyName(property));
    }

    protected virtual bool SetProperty<T>(T value, ref T field, [CallerMemberName] string propertyName = null)
    {
        if (field == null || !field.Equals(value))
        {
            field = value;
            OnPropertyChanged(propertyName);
            return true;
        }
        return false;
    }

    public void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public void OnPropertyChanged(Expression<Func<object>> property)
    {
        OnPropertyChanged(GetPropertyName(property));
    }

    protected string GetPropertyName(Expression<Func<object>> property)
    {
        var lambda = property as LambdaExpression;
        MemberExpression memberExpression;

        var unaryExpression = lambda.Body as UnaryExpression;
        if (unaryExpression != null)
        {
            memberExpression = unaryExpression.Operand as MemberExpression;
        }
        else
        {
            memberExpression = (MemberExpression) lambda.Body;
        }

        var propertyInfo = memberExpression?.Member as PropertyInfo;
        return propertyInfo?.Name ?? string.Empty;
    }
}

這樣做的一個巨大優勢是它會檢查值是否發生了變化。 這將最小化對視圖的更新調用。 對於您的示例，它可能如下所示：

public class Ethernet : PropertyChangedBase
{
    private string _timeStamp;

    public string TimeStamp
    {
        get { return _timeStamp; }
        set { SetProperty(value, ref _timeStamp); }
    }
}

如果您希望它真的很舒服，您可以為此編寫一個代碼片段。 這將是片段部分：

    <Snippet>
      <Declarations>
        <Literal>
          <ID>PropertyName</ID>
          <Type>String</Type>
          <ToolTip>The property name</ToolTip>
          <Default>NewProperty</Default>
        </Literal>
        <Literal>
          <ID>PropertyType</ID>
          <Type>
          </Type>
          <ToolTip>Replace with the type of the property</ToolTip>
          <Default>string</Default>
        </Literal>
        <Object>
          <ID>PrivateVariable</ID>
          <Type>Object</Type>
          <ToolTip>The name of the private variable</ToolTip>
          <Default>newPropertyValue</Default>
        </Object>
      </Declarations>
      <Code Language="csharp" Kind="method decl"><![CDATA[        private $PropertyType$ _$PrivateVariable$;
        public $PropertyType$ $PropertyName$
        {
            get { return _$PrivateVariable$; }
            set
            {
                SetProperty(value, ref _$PrivateVariable$);
            }
        }]]></Code>
    </Snippet>