触发OnPropertyChanged的更好方法

Question

我们有一个遵循MVVM模式的WPF项目.

在View Model中有很多代码如下所示:

    private string m_Fieldname;
    public string Fieldname
    {
        get { return m_Fieldname; }
        set
        {
            m_Fieldname = value;
            OnPropertyChanged("Fieldname");
        }
    }

有没有办法做到这需要更少的代码？

对这样的事情会很好:

[NotifyWhenChanged]
public string Fieldname { get; set ; }

Answer 1

你可以看看PostSharp.他们甚至在Data Binding上有一个样本.代码取自那里:

/// <summary>
/// Aspect that, when apply on a class, fully implements the interface 
/// <see cref="INotifyPropertyChanged"/> into that class, and overrides all properties to
/// that they raise the event <see cref="INotifyPropertyChanged.PropertyChanged"/>.
/// </summary>
[Serializable]
[IntroduceInterface( typeof(INotifyPropertyChanged), 
                     OverrideAction = InterfaceOverrideAction.Ignore )]
[MulticastAttributeUsage( MulticastTargets.Class, 
                          Inheritance = MulticastInheritance.Strict )]
public sealed class NotifyPropertyChangedAttribute : InstanceLevelAspect, 
                                                     INotifyPropertyChanged
{

    /// <summary>
    /// Field bound at runtime to a delegate of the method <c>OnPropertyChanged</c>.
    /// </summary>
    [ImportMember( "OnPropertyChanged", IsRequired = false)] 
    public Action<string> OnPropertyChangedMethod;

    /// <summary>
    /// Method introduced in the target type (unless it is already present);
    /// raises the <see cref="PropertyChanged"/> event.
    /// </summary>
    /// <param name="propertyName">Name of the property.</param>
    [IntroduceMember( Visibility = Visibility.Family, IsVirtual = true, 
                      OverrideAction = MemberOverrideAction.Ignore )]
    public void OnPropertyChanged( string propertyName )
    {
        if ( this.PropertyChanged != null )
        {
           this.PropertyChanged( this.Instance, 
                                  new PropertyChangedEventArgs( propertyName ) );
        }
    }

    /// <summary>
    /// Event introduced in the target type (unless it is already present);
    /// raised whenever a property has changed.
    /// </summary>
    [IntroduceMember( OverrideAction = MemberOverrideAction.Ignore )]
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Method intercepting any call to a property setter.
    /// </summary>
    /// <param name="args">Aspect arguments.</param>
    [OnLocationSetValueAdvice, 
     MulticastPointcut( Targets = MulticastTargets.Property, 
         Attributes = MulticastAttributes.Instance)]
    public void OnPropertySet( LocationInterceptionArgs args )
    {
        // Don't go further if the new value is equal to the old one.
        // (Possibly use object.Equals here).
        if ( args.Value == args.GetCurrentValue() ) return;

        // Actually sets the value.
        args.ProceedSetValue();

        // Invoke method OnPropertyChanged (our, the base one, or the overridden one).
        this.OnPropertyChangedMethod.Invoke( args.Location.Name );

    }
}

然后使用就像这样简单:

[NotifyPropertyChanged]
public class Shape
{
   public double X { get; set; }
   public double Y { get; set; }
}

从PostSharp站点获取并插入以完成答案的示例

Answer 2

看起来好像Framework 4.5略微简化了这个:

private string m_Fieldname;
public string Fieldname
{
    get { return m_Fieldname; }
    set
    {
        m_Fieldname = value;
        OnPropertyChanged();
    }
}

private void OnPropertyChanged([CallerMemberName] string propertyName = "none passed")
{
    // ... do stuff here ...
}

这并不会使您想要的程度自动化,但使用CallerMemberNameAttributemake将属性名称作为字符串传递是不必要的.

如果您正在使用安装了KB2468871的 Framework 4.0,则可以通过nuget安装Microsoft BCL兼容包,它还提供此属性.