触发属性更改事件的更短代码

Question

我有一个包含数十个属性的类需要引发属性更改事件，目前我的代码看起来像

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来编写这种代码，我对每个属性都进行了过多的复制/粘贴操作，我觉得必须有更好的方法。

Answer 1

引用的代码在编写时不是线程安全的。请参阅Pattern for implementing INotifyPropertyChanged? 为什么下面的代码更好，以及在接受的回复中指向 Eric Lippert 博客的链接，为什么故事没有就此结束。

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

有关实际问题的答案，请参阅Implementing INotifyPropertyChanged - does a better way exist?，包括此 C# 6.0 快捷方式。

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

Answer 2

看看这个答案：https://stackoverflow.com/a/2339904/259769

我在提供和扩展方法中的代码替换了大部分设置代码，让您将代码缩短为：

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); }
    }
}

此代码的另一个明显优势是它会立即针对属性名称进行强类型化。

Answer 3

在MVVM模式中，经常使用properties changed/ing，一个典型的基本解决方案如下：

  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

我爱上了这门课：

[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;
    }
}

这样做的一个巨大优势是它会检查值是否发生了变化。这将最小化对视图的更新调用。对于您的示例，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); }
    }
}

如果你想要它真的很舒服，你可以为此编写一个代码 sn-p。这将是 sn-p 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>