微软应该为INotifyPropertyChanged实现一些时髦的东西,就像在自动属性中,只需要指定{get;设置;通知;} 我认为这样做很有意义。或者做这个手术有什么并发症吗?

我们能在属性中实现类似notify的东西吗。在你的类中实现INotifyPropertyChanged是否有一个优雅的解决方案,或者唯一的方法是在每个属性中引发PropertyChanged事件。

如果不是,我们可以写一些东西来自动生成一段代码来引发PropertyChanged事件?


当前回答

另一个组合解决方案是使用StackFrame:

public class BaseViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void Set<T>(ref T field, T value)
    {
        MethodBase method = new StackFrame(1).GetMethod();
        field = value;
        Raise(method.Name.Substring(4));
    }

    protected void Raise(string propertyName)
    {
        var temp = PropertyChanged;
        if (temp != null)
        {
            temp(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

用法:

public class TempVM : BaseViewModel
{
    private int _intP;
    public int IntP
    {
        get { return _intP; }
        set { Set<int>(ref _intP, value); }
    }
}

其他回答

这是一个Unity3D或非callermembername版本的NotifyPropertyChanged

public abstract class Bindable : MonoBehaviour, INotifyPropertyChanged
{
    private readonly Dictionary<string, object> _properties = new Dictionary<string, object>();
    private static readonly StackTrace stackTrace = new StackTrace();
    public event PropertyChangedEventHandler PropertyChanged;

    /// <summary>
    ///     Resolves a Property's name from a Lambda Expression passed in.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="property"></param>
    /// <returns></returns>
    internal string GetPropertyName<T>(Expression<Func<T>> property)
    {
        var expression = (MemberExpression) property.Body;
        var propertyName = expression.Member.Name;

        Debug.AssertFormat(propertyName != null, "Bindable Property shouldn't be null!");
        return propertyName;
    }

    #region Notification Handlers

    /// <summary>
    ///     Notify's all other objects listening that a value has changed for nominated propertyName
    /// </summary>
    /// <param name="propertyName"></param>
    internal void NotifyOfPropertyChange(string propertyName)
    {
        OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    /// <summary>
    ///     Notifies subscribers of the property change.
    /// </summary>
    /// <typeparam name="TProperty">The type of the property.</typeparam>
    /// <param name="property">The property expression.</param>
    internal void NotifyOfPropertyChange<TProperty>(Expression<Func<TProperty>> property)
    {
        var propertyName = GetPropertyName(property);
        NotifyOfPropertyChange(propertyName);
    }

    /// <summary>
    ///     Raises the <see cref="PropertyChanged" /> event directly.
    /// </summary>
    /// <param name="e">The <see cref="PropertyChangedEventArgs" /> instance containing the event data.</param>
    internal void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        var handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, e);
        }
    }

    #endregion

    #region Getters

    /// <summary>
    ///     Gets the value of a property
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="name"></param>
    /// <returns></returns>
    internal T Get<T>(Expression<Func<T>> property)
    {
        var propertyName = GetPropertyName(property);
        return Get<T>(GetPropertyName(property));
    }

    /// <summary>
    ///     Gets the value of a property automatically based on its caller.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <returns></returns>
    internal T Get<T>()
    {
        var name = stackTrace.GetFrame(1).GetMethod().Name.Substring(4); // strips the set_ from name;
        return Get<T>(name);
    }

    /// <summary>
    ///     Gets the name of a property based on a string.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="name"></param>
    /// <returns></returns>
    internal T Get<T>(string name)
    {
        object value = null;
        if (_properties.TryGetValue(name, out value))
            return value == null ? default(T) : (T) value;
        return default(T);
    }

    #endregion

    #region Setters

    /// <summary>
    ///     Sets the value of a property whilst automatically looking up its caller name.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="value"></param>
    internal void Set<T>(T value)
    {
        var propertyName = stackTrace.GetFrame(1).GetMethod().Name.Substring(4); // strips the set_ from name;
        Set(value, propertyName);
    }

    /// <summary>
    ///     Sets the value of a property
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="value"></param>
    /// <param name="name"></param>
    internal void Set<T>(T value, string propertyName)
    {
        Debug.Assert(propertyName != null, "name != null");
        if (Equals(value, Get<T>(propertyName)))
            return;
        _properties[propertyName] = value;
        NotifyOfPropertyChange(propertyName);
    }

    /// <summary>
    ///     Sets the value of a property based off an Expression (()=>FieldName)
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="value"></param>
    /// <param name="property"></param>
    internal void Set<T>(T value, Expression<Func<T>> property)
    {
        var propertyName = GetPropertyName(property);

        Debug.Assert(propertyName != null, "name != null");

        if (Equals(value, Get<T>(propertyName)))
            return;
        _properties[propertyName] = value;
        NotifyOfPropertyChange(propertyName);
    }

    #endregion
}

这段代码允许你像这样编写属性支持字段:

  public string Text
    {
        get { return Get<string>(); }
        set { Set(value); }
    }

此外,在resharper中,如果你创建了一个模式/搜索片段,你也可以通过将简单的道具字段转换为上面的支持来自动化你的工作流程。

搜索模式:

public $type$ $fname$ { get; set; }

替换模式:

public $type$ $fname$
{
    get { return Get<$type$>(); }
    set { Set(value); }
}

在实现这些类型的属性时,你可能要考虑的其他事情是INotifyPropertyChang *ed *ing都使用事件参数类。

如果要设置大量的属性,那么事件参数类实例的数量可能非常大,您应该考虑缓存它们,因为它们是可能发生字符串爆炸的区域之一。

看一下这个实现,并解释为什么要考虑它。

Josh Smiths博客

另一个想法……

 public class ViewModelBase : INotifyPropertyChanged
{
    private Dictionary<string, object> _propertyStore = new Dictionary<string, object>();
    protected virtual void SetValue<T>(T value, [CallerMemberName] string propertyName="") {
        _propertyStore[propertyName] = value;
        OnPropertyChanged(propertyName);
    }
    protected virtual T GetValue<T>([CallerMemberName] string propertyName = "")
    {
        object ret;
        if (_propertyStore.TryGetValue(propertyName, out ret))
        {
            return (T)ret;
        }
        else
        {
            return default(T);
        }
    }

    //Usage
    //public string SomeProperty {
    //    get { return GetValue<string>();  }
    //    set { SetValue(value); }
    //}

    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string propertyName)
    {
        var temp = PropertyChanged;
        if (temp != null)
            temp.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

让我介绍一下我自己的方法,叫做Yappi。 它属于运行时代理|派生类生成器,向现有对象或类型添加新功能,如种姓项目的动态代理。

它允许在基类中实现INotifyPropertyChanged一次,然后以以下风格声明派生类,仍然支持INotifyPropertyChanged用于新属性:

public class Animal:Concept
{
    protected Animal(){}
    public virtual string Name { get; set; }
    public virtual int Age { get; set; }
}

派生类或代理构造的复杂性可以隐藏在下面这行代码后面:

var animal = Concept.Create<Animal>.New();

所有的INotifyPropertyChanged实现工作可以像这样完成:

public class Concept:INotifyPropertyChanged
{
    //Hide constructor
    protected Concept(){}

    public static class Create<TConcept> where TConcept:Concept
    {
        //Construct derived Type calling PropertyProxy.ConstructType
        public static readonly Type Type = PropertyProxy.ConstructType<TConcept, Implementation<TConcept>>(new Type[0], true);
        //Create constructing delegate calling Constructor.Compile
        public static Func<TConcept> New = Constructor.Compile<Func<TConcept>>(Type);
    }


    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(PropertyChangedEventArgs eventArgs)
    {
        var caller = PropertyChanged;
        if(caller!=null)
        {
            caller(this, eventArgs);
        }
    }

    //define implementation
    public class Implementation<TConcept> : DefaultImplementation<TConcept> where TConcept:Concept
    {
        public override Func<TBaseType, TResult> OverrideGetter<TBaseType, TDeclaringType, TConstructedType, TResult>(PropertyInfo property)
        {
            return PropertyImplementation<TBaseType, TDeclaringType>.GetGetter<TResult>(property.Name);
        }
        /// <summary>
        /// Overriding property setter implementation.
        /// </summary>
        /// <typeparam name="TBaseType">Base type for implementation. TBaseType must be TConcept, and inherits all its constraints. Also TBaseType is TDeclaringType.</typeparam>
        /// <typeparam name="TDeclaringType">Type, declaring property.</typeparam>
        /// <typeparam name="TConstructedType">Constructed type. TConstructedType is TDeclaringType and TBaseType.</typeparam>
        /// <typeparam name="TResult">Type of property.</typeparam>
        /// <param name="property">PropertyInfo of property.</param>
        /// <returns>Delegate, corresponding to property setter implementation.</returns>
        public override Action<TBaseType, TResult> OverrideSetter<TBaseType, TDeclaringType, TConstructedType, TResult>(PropertyInfo property)
        {
            //This code called once for each declared property on derived type's initialization.
            //EventArgs instance is shared between all events for each concrete property.
            var eventArgs = new PropertyChangedEventArgs(property.Name);
            //get delegates for base calls.
            Action<TBaseType, TResult> setter = PropertyImplementation<TBaseType, TDeclaringType>.GetSetter<TResult>(property.Name);
            Func<TBaseType, TResult> getter = PropertyImplementation<TBaseType, TDeclaringType>.GetGetter<TResult>(property.Name);

            var comparer = EqualityComparer<TResult>.Default;

            return (pthis, value) =>
            {//This code executes each time property setter is called.
                if (comparer.Equals(value, getter(pthis))) return;
                //base. call
                setter(pthis, value);
                //Directly accessing Concept's protected method.
                pthis.OnPropertyChanged(eventArgs);
            };
        }
    }
}

它对于重构是完全安全的,在类型构造后不使用反射,并且足够快。

从。net 4.5开始,终于有了一个简单的方法。

. net 4.5引入了一个新的调用者信息属性。

private void OnPropertyChanged<T>([CallerMemberName]string caller = null) {
     // make sure only to call this if the value actually changes

     var handler = PropertyChanged;
     if (handler != null) {
        handler(this, new PropertyChangedEventArgs(caller));
     }
}

在函数中添加比较器可能也是一个好主意。

EqualityComparer<T>.Default.Equals

更多的例子在这里和这里

参见调用者信息(c#和Visual Basic)