序言

       借助WPF/Sliverlight强大的数据绑定功能，可以比实现比MFC，WinForm更加优雅轻松的数据绑定。但是在使用WPF/Silverlight绑定时，有件事情是很苦恼的：当ViewModel对象放生改变，需要通知UI。我们可以让VM对象实现INotifyPropertyChanged接口，通过事件来通知UI。但问题就出现这里……

一，描述问题

        情形：现在需要将一个Person对象的Name熟悉双向绑定到UI中的TextBox，的确这是一件很简单的事情，但还是描述下：

        XAML：

<TextBox Text="{Binding Name,Mode=TwoWay}"/>

       C# Code：

public class Person : INotifyPropertyChanged{private string m_Name;public string Name{get { return m_Name; }set {if (m_Name == value) return; m_Name = value;this.Notify("Name");}}public Person(){this.m_Name = "墨梅，在这里......";}public event PropertyChangedEventHandler PropertyChanged;public void Notify(string propertyName){PropertyChangedEventHandler handler = this.PropertyChanged;if (handler != null)handler(this, new PropertyChangedEventArgs(propertyName));}}

       是的，这就可以实现了。但是这里一个问题困惑我，曾经就在this.Notify("Name")，将参数写错，UI迟迟得不到响应。这个错误很难发现！！！也很难跟踪，但是这个细微的错误可以导致一个很严重的运行时错误。这的确是一件很苦恼的事情。

二解决问题

方法一：添加验证

public event PropertyChangedEventHandler PropertyChanged;protected virtual void OnPropertyChanged(string propertyName)
{this.VerifyPropertyName(propertyName);PropertyChangedEventHandler handler = this.PropertyChanged;if (handler != null){var e = new PropertyChangedEventArgs(propertyName);handler(this, e);}
}[Conditional("DEBUG")]
[DebuggerStepThrough]
public void VerifyPropertyName(string propertyName)
{// Verify that the property name matches a real,  // public, instance property on this object.if (TypeDescriptor.GetProperties(this)[propertyName] == null){string msg = "Invalid property name: " + propertyName;if (this.ThrowOnInvalidPropertyName)throw new Exception(msg);elseDebug.Fail(msg);}
}

     这里对验证事件参数使用条件编译[Conditional(“DEBUG”)],在release版本中这个函数是不会调用的，比使用#if 等有更明显有优势。

     这个方法虽然可以达到目的，但是还是那么的别扭，必须到运行时才能知道是否有错误，所以还是不怎么好。

方法二，使用Lambda表达式，静态扩展语法

public static class NotificationExtensions{public static void Notify(this PropertyChangedEventHandler eventHandler, Expression<Func<object>> expression){if( null == eventHandler ){return;}var lambda = expression as LambdaExpression;MemberExpression memberExpression;if (lambda.Body is UnaryExpression){var unaryExpression = lambda.Body as UnaryExpression;memberExpression = unaryExpression.Operand as MemberExpression;}else{memberExpression = lambda.Body as MemberExpression;}var constantExpression = memberExpression.Expression as ConstantExpression;var propertyInfo = memberExpression.Member as PropertyInfo;foreach (var del in eventHandler.GetInvocationList()){del.DynamicInvoke(new object[] {constantExpression.Value, new PropertyChangedEventArgs(propertyInfo.Name)});}}}

这里用使用的静态扩展语法，我还是比较喜欢这个的，但是并不是所有人都喜欢哦。如何使用呢：

public class Employee : INotifyPropertyChanged{public event PropertyChangedEventHandler PropertyChanged;private string _firstName;public string FirstName {get { return this._firstName; }set{this._firstName = value;this.PropertyChanged.Notify(()=>this.FirstName);}}}

这里还可以添加一个很实用的扩展：

public static void SubscribeToChange<T>(this T objectThatNotifies, Expression<Func<object>> expression, PropertyChangedEventHandler<T> handler)where T : INotifyPropertyChanged{objectThatNotifies.PropertyChanged +=(s, e) =>{var lambda = expression as LambdaExpression;MemberExpression memberExpression;if (lambda.Body is UnaryExpression){var unaryExpression = lambda.Body as UnaryExpression;memberExpression = unaryExpression.Operand as MemberExpression;}else{memberExpression = lambda.Body as MemberExpression;}var propertyInfo = memberExpression.Member as PropertyInfo;if(e.PropertyName.Equals(propertyInfo.Name)){handler(objectThatNotifies);}};}

通过上面的代码，可以订阅熟悉改变事件,如：

myObject.SubscripeToChange(()=>myObject.SomeProperty,SomeProperty_Changed); And then your handler would look like this:private void SomeProperty_Changed(MyObject myObject)
{/* ... implement something here */
}

方法三，net4.5，框架提供的解决方法

private string m_myProperty;
public string MyProperty
{get { return m_myProperty; }set{m_myProperty = value;OnPropertyChanged();}
}private void OnPropertyChanged([CallerMemberName] string propertyName = "none passed")
{// ... do stuff here ...
}

属性CallerMemberName的解决办法和方法二是基本相同的，不同的是这个在net框架中解决的。更多信息可以查看CallerMemberName，net4.5还提供了

CallerFilePath，CallerLineNumber，这几很有用的语法

方法四，这个也不错哦

public static class SymbolExtensions{public static string GetPropertySymbol<T,R>(this T obj, Expression<Func<T,R>> expr){return ((MemberExpression)expr.Body).Member.Name;}}public class ConversionOptions : INotifyPropertyChanged{private string _outputPath;public string OutputPath{get { return _outputPath;}set{_outputPath = value;OnPropertyChanged(o => o.OutputPath);}}private string _blogName;public string BlogName{get { return _blogName;}set{_blogName = value;OnPropertyChanged(o => o.BlogName);}}private string _secretWord;public string SecretWord{get { return _secretWord; }set{_secretWord = value;OnPropertyChanged(o => o.SecretWord);}}protected virtual void OnPropertyChanged<R>(Expression<Func<ConversionOptions, R>> propertyExpr){OnPropertyChanged(this.GetPropertySymbol(propertyExpr));}protected virtual void OnPropertyChanged(string propertyName){if (PropertyChanged != null)PropertyChanged(this, new PropertyChangedEventArgs(propertyName));}public event PropertyChangedEventHandler PropertyChanged;}

注释：这里还有更多参考信息，您可以在这里了解更加清楚：