C# 触发OnPropertyChanged的更好方法

我们有一个遵循MVVM模式的WPF项目

在视图模型中，有许多代码如下所示：

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

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

private int _value;
public int Value
{
    get { return _value; }
    set { UpdatePropertyField(ref _value, value); }
}

有没有一种方法可以做到这一点，它需要更少的代码

有这样的东西会很好：

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

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

private int _value;
public int Value
{
    get { return _value; }
    set { UpdatePropertyField(ref _value, value); }
}

你可以看看。他们甚至有一个样本。代码取自此处：

/// <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 );

    }
}

---

摘自PostSharp站点并插入用于完成答案的示例

Josh Smith有一篇关于使用DynamicObject实现此目的的好文章

---

基本上，它包括从DynamicObject继承，然后连接到TrySetMember。不幸的是，仅限CLR 4.0，虽然在早期版本中也可以使用ContextBoundObject，但这可能会影响性能，主要适用于远程处理\WCF。

看起来框架4.5稍微简化了这一点：

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 ...
}

这并没有将事情自动化到您要查找的程度，但是使用会使属性名作为字符串传递变得不必要

---

如果您使用的是安装了的Framework 4.0，则可以通过安装Microsoft BCL Compatibility Pack，它也提供此属性。

好，这不会清理代码，但会缩短编写所有代码的时间。我现在可以在几分钟内浏览20多处房产的列表

首先，您需要定义所有私有变量，我假设您的第一个字符是小写。现在，当宏删除原始行时，将这些变量复制到另一个列表中

例如：

private int something1 = 0;
private int something2 = 0;
private int something3 = 0;
private int something4 = 0;
private int something5 = 0;
private int something6 = 0;

然后将光标放在该行的某个位置并运行此宏。同样，这将用公共属性替换该行，因此确保在类中在此之前定义了相同的私有成员变量

我相信这个脚本可以被清理，但它今天为我节省了数小时的枯燥工作

Sub TemporaryMacro()
    DTE.ActiveDocument.Selection.StartOfLine(VsStartOfLineOptions.VsStartOfLineOptionsFirstText)
    DTE.ActiveDocument.Selection.Delete(7)
    DTE.ActiveDocument.Selection.Text = "public"
    DTE.ActiveDocument.Selection.CharRight()
    DTE.ExecuteCommand("Edit.Find")
    DTE.Find.FindWhat = " "
    DTE.Find.Target = vsFindTarget.vsFindTargetCurrentDocument
    DTE.Find.MatchCase = False
    DTE.Find.MatchWholeWord = False
    DTE.Find.Backwards = False
    DTE.Find.MatchInHiddenText = False
    DTE.Find.PatternSyntax = vsFindPatternSyntax.vsFindPatternSyntaxLiteral
    DTE.Find.Action = vsFindAction.vsFindActionFind
    If (DTE.Find.Execute() = vsFindResult.vsFindResultNotFound) Then
        Throw New System.Exception("vsFindResultNotFound")
    End If
    DTE.ActiveDocument.Selection.CharRight()
    DTE.ActiveDocument.Selection.WordRight(True)
    DTE.ActiveDocument.Selection.CharLeft(True)
    DTE.ActiveDocument.Selection.Copy()
    DTE.ActiveDocument.Selection.CharLeft()
    DTE.ActiveDocument.Selection.CharRight(True)
    DTE.ActiveDocument.Selection.ChangeCase(VsCaseOptions.VsCaseOptionsUppercase)
    DTE.ActiveDocument.Selection.EndOfLine()
    DTE.ActiveDocument.Selection.StartOfLine(VsStartOfLineOptions.VsStartOfLineOptionsFirstText)
    DTE.ExecuteCommand("Edit.Find")
    DTE.Find.FindWhat = " = "
    DTE.Find.Target = vsFindTarget.vsFindTargetCurrentDocument
    DTE.Find.MatchCase = False
    DTE.Find.MatchWholeWord = False
    DTE.Find.Backwards = False
    DTE.Find.MatchInHiddenText = False
    DTE.Find.PatternSyntax = vsFindPatternSyntax.vsFindPatternSyntaxLiteral
    DTE.Find.Action = vsFindAction.vsFindActionFind
    If (DTE.Find.Execute() = vsFindResult.vsFindResultNotFound) Then
        Throw New System.Exception("vsFindResultNotFound")
    End If
    DTE.ActiveDocument.Selection.CharLeft()
    DTE.ActiveDocument.Selection.EndOfLine(True)
    DTE.ActiveDocument.Selection.Delete()
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "{"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "get { return "
    DTE.ActiveDocument.Selection.Paste()
    DTE.ActiveDocument.Selection.Text = "; }"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "set"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "{"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "if("
    DTE.ActiveDocument.Selection.Paste()
    DTE.ActiveDocument.Selection.Text = " != value)"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "{"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Paste()
    DTE.ActiveDocument.Selection.Text = " = value;"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "OnPropertyChanged("""
    DTE.ActiveDocument.Selection.Paste()
    DTE.ActiveDocument.Selection.Text = """);"
    DTE.ActiveDocument.Selection.StartOfLine(VsStartOfLineOptions.VsStartOfLineOptionsFirstText)
    DTE.ExecuteCommand("Edit.Find")
    DTE.Find.FindWhat = """"
    DTE.Find.Target = vsFindTarget.vsFindTargetCurrentDocument
    DTE.Find.MatchCase = False
    DTE.Find.MatchWholeWord = False
    DTE.Find.Backwards = False
    DTE.Find.MatchInHiddenText = False
    DTE.Find.PatternSyntax = vsFindPatternSyntax.vsFindPatternSyntaxLiteral
    DTE.Find.Action = vsFindAction.vsFindActionFind
    If (DTE.Find.Execute() = vsFindResult.vsFindResultNotFound) Then
        Throw New System.Exception("vsFindResultNotFound")
    End If
    DTE.ActiveDocument.Selection.CharRight()
    DTE.ActiveDocument.Selection.CharRight(True)
    DTE.ActiveDocument.Selection.ChangeCase(VsCaseOptions.VsCaseOptionsUppercase)
    DTE.ActiveDocument.Selection.Collapse()
    DTE.ActiveDocument.Selection.EndOfLine()
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "}"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "}"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.Text = "}"
    DTE.ActiveDocument.Selection.NewLine()
    DTE.ActiveDocument.Selection.LineDown()
    DTE.ActiveDocument.Selection.EndOfLine()
End Sub

---

IMHO，在公认的答案中，后夏普方法非常好，当然是对所问问题的直接回答

但是，对于那些不能或不愿使用PostSharp之类的工具来扩展C语言语法的人来说，使用实现

INotifyPropertyChanged

的基类避免代码重复可以获得最大的好处。有很多例子，但到目前为止，没有一个被纳入这个有用且被广泛使用的问题中，因此我通常使用的版本如下：

/// <summary>
/// Base class for classes that need to implement <see cref="INotifyPropertyChanged"/>
/// </summary>
public class NotifyPropertyChangedBase : INotifyPropertyChanged
{
    /// <summary>
    /// Raised when a property value changes
    /// </summary>
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    /// Updates a field for a named property
    /// </summary>
    /// <typeparam name="T">The type of the field</typeparam>
    /// <param name="field">The field itself, passed by-reference</param>
    /// <param name="newValue">The new value for the field</param>
    /// <param name="onChangedCallback">A delegate to be called if the field value has changed. The old value of the field is passed to the delegate.</param>
    /// <param name="propertyName">The name of the associated property</param>
    protected void UpdatePropertyField<T>(ref T field, T newValue,
        Action<T> onChangedCallback = null,
        [CallerMemberName] string propertyName = null)
    {
        if (EqualityComparer<T>.Default.Equals(field, newValue))
        {
            return;
        }

        T oldValue = field;

        field = newValue;
        onChangedCallback?.Invoke(oldValue);
        OnPropertyChanged(propertyName);
    }

    /// <summary>
    /// Raises the <see cref="PropertyChanged"/> event.
    /// </summary>
    /// <param name="propertyName">The name of the property that has been changed</param>
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

不像PostSharp方法那样能够将代码属性应用于自动实现的属性，但在加快视图模型和其他类似类型的实现方面仍有很大的进步

上述区别于其他一些实现的关键功能：

使用

EqualityComparer.Default

比较相等性。这确保了可以在不装箱的情况下比较值类型（常见的替代方法是

object.Equals（object，object）

）。

IEqualityComparer

实例是缓存的，因此在对任何给定类型的

T

进行第一次比较之后，它的效率非常高

OnPropertyChanged（）

方法是

virtual

。这允许派生类型以集中的方式轻松有效地处理属性更改事件，而无需订阅

PropertyChanged

事件本身（例如，对于多个继承级别）当然，相对于引发实际的

PropertyChanged

事件，派生类型还可以更好地控制如何以及何时处理属性更改事件

---

我会使用PropertyChanged.Fody NuGet包。简单到：

[PropertyChanged.ImplementPropertyChanged]
public class MyViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged = (sender, e) => { };

    public string Prop1 { get; set; }
    public string Prop2 { get; set; }
}

所有公共财产将在幕后引发财产变更事件

---

更新版本中的p.S.语法已更改。此示例适用于1.52.1版

是否存在性能损失？动态是相当缓慢的，属性更改可能会经常发生。还是我错了？这肯定比用经典的方式做慢，尤其是在涉及到try/catch块的情况下。像往常一样，有一个折衷的办法。你不应该总是检查

如果（m_Fieldname！=value）{…}

？我知道这是更多的代码，但是如果属性没有改变，那么提升

PropertyChanged

似乎是不正确的。就我个人而言，我只是在一个基本的ObservableItem类中有一个SetProperty方法（我的ViewModelBase就是从这个类派生的），它处理所有通知、相等性检查、属性设置等。它很好而且干净，而且你仍然只有一个班轮。另外，只需设置一个代码片段来创建它们，而且它快速、简单、标准化。既然postsharp是一个付费工具，我们能在2018年找到一个方法来实现这一点吗？如果我不想让X在PropertyChanged上开火怎么办，“我只想你炒掉它？@thenonhacker你可以用

IgnoreAutoChangeNotificationAttribute

来装饰一个属性，让它被忽略。见文件：和