MVVM之INotifyPropertyChanged接口的几种实现方式（2）

最新推荐文章于 2022-03-30 13:25:20 发布

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最新推荐文章于 2022-03-30 13:25:20 发布

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本文介绍了MVVM模式下实现INotifyPropertyChanged接口的多种方法，包括使用Lambda表达式的静态扩展语法，以及.NET 4.5框架提供的CallerMemberName特性。文章详细展示了每种方法的代码实现，并给出了如何订阅属性改变事件的示例。

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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> 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(this T objectThatNotifies, Expression<Func> expression, PropertyChangedEventHandler 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;
}