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
如果你在。net 4.5中使用动态，你不需要担心INotifyPropertyChanged。
dynamic obj = new ExpandoObject();
obj.Name = "John";
如果Name被绑定到某个控件，它就可以正常工作。
其他回答
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); }
}
}
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); }
}
我实际上还没有机会尝试这个自己，但下次我设置一个大需求的INotifyPropertyChanged项目，我打算写一个Postsharp属性，将在编译时注入代码。喜欢的东西:
[NotifiesChange]
public string FirstName { get; set; }
将成为:
private string _firstName;
public string FirstName
{
get { return _firstname; }
set
{
if (_firstname != value)
{
_firstname = value;
OnPropertyChanged("FirstName")
}
}
}
我不确定这在实践中是否有效，我需要坐下来尝试一下，但我不明白为什么不。我可能需要让它接受一些参数的情况下，超过一个OnPropertyChanged需要被触发(如果，例如，我有一个FullName属性在上面的类)
目前我在Resharper使用一个自定义模板，但即使这样，我也厌倦了我所有的属性太长。
啊，一个快速的谷歌搜索(我应该在写这篇文章之前做的)显示至少有一个人在这里之前做过类似的事情。跟我想的不完全一样，但也足以证明这个理论是正确的。
我用这种方式解决(这有点费力，但在运行时肯定更快)。
在VB中(抱歉，但我认为用c#翻译它并不难)，我用RE做了这个替换:
(?<Attr><(.*ComponentModel\.)Bindable\(True\)>)( |\r\n)*(?<Def>(Public|Private|Friend|Protected) .*Property )(?<Name>[^ ]*) As (?<Type>.*?)[ |\r\n](?![ |\r\n]*Get)
:
Private _${Name} As ${Type}\r\n${Attr}\r\n${Def}${Name} As ${Type}\r\nGet\r\nReturn _${Name}\r\nEnd Get\r\nSet (Value As ${Type})\r\nIf _${Name} <> Value Then \r\n_${Name} = Value\r\nRaiseEvent PropertyChanged(Me, New ComponentModel.PropertyChangedEventArgs("${Name}"))\r\nEnd If\r\nEnd Set\r\nEnd Property\r\n
这样转换所有代码:
<Bindable(True)>
Protected Friend Property StartDate As DateTime?
In
Private _StartDate As DateTime?
<Bindable(True)>
Protected Friend Property StartDate As DateTime?
Get
Return _StartDate
End Get
Set(Value As DateTime?)
If _StartDate <> Value Then
_StartDate = Value
RaiseEvent PropertyChange(Me, New ComponentModel.PropertyChangedEventArgs("StartDate"))
End If
End Set
End Property
如果我想有一个更可读的代码，我可以相反，只是做下面的替换:
Private _(?<Name>.*) As (?<Type>.*)[\r\n ]*(?<Attr><(.*ComponentModel\.)Bindable\(True\)>)[\r\n ]*(?<Def>(Public|Private|Friend|Protected) .*Property )\k<Name> As \k<Type>[\r\n ]*Get[\r\n ]*Return _\k<Name>[\r\n ]*End Get[\r\n ]*Set\(Value As \k<Type>\)[\r\n ]*If _\k<Name> <> Value Then[\r\n ]*_\k<Name> = Value[\r\n ]*RaiseEvent PropertyChanged\(Me, New (.*ComponentModel\.)PropertyChangedEventArgs\("\k<Name>"\)\)[\r\n ]*End If[\r\n ]*End Set[\r\n ]*End Property
With
${Attr} ${Def} ${Name} As ${Type}
我抛出来替换set方法的IL代码，但我不能用IL编写大量编译代码…如果哪天我写了，我就说你!
是的，更好的办法当然存在。 下面就是:
循序渐进的教程由我缩减，基于这篇有用的文章。
创建新项目 将城堡核心包安装到项目中
安装包的城堡。核心
只安装mvvm light库
安装包MvvmLightLibs
在项目中添加两个类:
NotifierInterceptor
public class NotifierInterceptor : IInterceptor
{
private PropertyChangedEventHandler handler;
public static Dictionary<String, PropertyChangedEventArgs> _cache =
new Dictionary<string, PropertyChangedEventArgs>();
public void Intercept(IInvocation invocation)
{
switch (invocation.Method.Name)
{
case "add_PropertyChanged":
handler = (PropertyChangedEventHandler)
Delegate.Combine(handler, (Delegate)invocation.Arguments[0]);
invocation.ReturnValue = handler;
break;
case "remove_PropertyChanged":
handler = (PropertyChangedEventHandler)
Delegate.Remove(handler, (Delegate)invocation.Arguments[0]);
invocation.ReturnValue = handler;
break;
default:
if (invocation.Method.Name.StartsWith("set_"))
{
invocation.Proceed();
if (handler != null)
{
var arg = retrievePropertyChangedArg(invocation.Method.Name);
handler(invocation.Proxy, arg);
}
}
else invocation.Proceed();
break;
}
}
private static PropertyChangedEventArgs retrievePropertyChangedArg(String methodName)
{
PropertyChangedEventArgs arg = null;
_cache.TryGetValue(methodName, out arg);
if (arg == null)
{
arg = new PropertyChangedEventArgs(methodName.Substring(4));
_cache.Add(methodName, arg);
}
return arg;
}
}
ProxyCreator
public class ProxyCreator
{
public static T MakeINotifyPropertyChanged<T>() where T : class, new()
{
var proxyGen = new ProxyGenerator();
var proxy = proxyGen.CreateClassProxy(
typeof(T),
new[] { typeof(INotifyPropertyChanged) },
ProxyGenerationOptions.Default,
new NotifierInterceptor()
);
return proxy as T;
}
}
创建你的视图模型，例如:
-
public class MainViewModel
{
public virtual string MainTextBox { get; set; }
public RelayCommand TestActionCommand
{
get { return new RelayCommand(TestAction); }
}
public void TestAction()
{
Trace.WriteLine(MainTextBox);
}
}
将绑定放入xaml: <TextBox Text="{绑定MainTextBox}" ></TextBox> . <Button Command="{Binding TestActionCommand}" >Test</Button> . 在代码隐藏文件MainWindow.xaml.cs中放入如下代码行:
DataContext = ProxyCreator.MakeINotifyPropertyChanged<MainViewModel>（）;
享受。
注意! !所有有界属性都应该用 关键字virtual，因为它们被城堡代理用于重写。
