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?
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
我把它作为一个片段保存下来。c# 6为调用处理程序添加了一些不错的语法。
// INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
private void Set<T>(ref T property, T value, [CallerMemberName] string propertyName = null)
{
if (EqualityComparer<T>.Default.Equals(property, value) == false)
{
property = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
其他回答
看这里:http://dotnet-forum.de/blogs/thearchitect/archive/2012/11/01/die-optimale-implementierung-des-inotifypropertychanged-interfaces.aspx
它是用德语写的,但你可以下载ViewModelBase.cs。cs-File中的所有注释都是用英语写的。
使用这个ViewModelBase-Class,可以实现类似于众所周知的依赖属性的可绑定属性:
public string SomeProperty
{
get { return GetValue( () => SomeProperty ); }
set { SetValue( () => SomeProperty, value ); }
}
没有使用postsharp之类的东西,我使用的最小版本使用如下内容:
public class Data : INotifyPropertyChanged
{
// boiler-plate
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
protected bool SetField<T>(ref T field, T value, string propertyName)
{
if (EqualityComparer<T>.Default.Equals(field, value)) return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
// props
private string name;
public string Name
{
get { return name; }
set { SetField(ref name, value, "Name"); }
}
}
每个属性就像这样:
private string name;
public string Name
{
get { return name; }
set { SetField(ref name, value, "Name"); }
}
这并不大;如果需要,它也可以用作基类。SetField的bool返回值告诉你它是否为no-op,以防你想应用其他逻辑。
或者用c# 5更简单:
protected bool SetField<T>(ref T field, T value,
[CallerMemberName] string propertyName = null)
{...}
可以这样称呼:
set { SetField(ref name, value); }
编译器会自动添加“Name”。
c# 6.0使实现更容易:
protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
...现在是c# 7:
protected void OnPropertyChanged(string propertyName)
=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
protected bool SetField<T>(ref T field, T value,[CallerMemberName] string propertyName = null)
{
if (EqualityComparer<T>.Default.Equals(field, value)) return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
private string name;
public string Name
{
get => name;
set => SetField(ref name, value);
}
并且,使用c# 8和Nullable引用类型,它看起来像这样:
public event PropertyChangedEventHandler? PropertyChanged;
protected void OnPropertyChanged(string propertyName) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
protected bool SetField<T>(ref T field, T value, [CallerMemberName] string propertyName = "")
{
if (EqualityComparer<T>.Default.Equals(field, value)) return false;
field = value;
OnPropertyChanged(propertyName);
return true;
}
private string name;
public string Name
{
get => name;
set => SetField(ref name, value);
}
还有Fody,它有一个AddINotifyPropertyChangedInterface插件,它让你这样写:
[AddINotifyPropertyChangedInterface]
public class Person
{
public string GivenNames { get; set; }
public string FamilyName { get; set; }
}
...并在编译时注入属性更改通知。
Prism 5实现:
public abstract class BindableBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual bool SetProperty<T>(ref T storage,
T value,
[CallerMemberName] string propertyName = null)
{
if (object.Equals(storage, value)) return false;
storage = value;
this.OnPropertyChanged(propertyName);
return true;
}
protected void OnPropertyChanged(string propertyName)
{
var eventHandler = this.PropertyChanged;
if (eventHandler != null)
{
eventHandler(this, new PropertyChangedEventArgs(propertyName));
}
}
protected void OnPropertyChanged<T>(Expression<Func<T>> propertyExpression)
{
var propertyName = PropertySupport.ExtractPropertyName(propertyExpression);
this.OnPropertyChanged(propertyName);
}
}
public static class PropertySupport
{
public static string ExtractPropertyName<T>(Expression<Func<T>> propertyExpression)
{
if (propertyExpression == null)
{
throw new ArgumentNullException("propertyExpression");
}
var memberExpression = propertyExpression.Body as MemberExpression;
if (memberExpression == null)
{
throw new ArgumentException("The expression is not a member access expression.", "propertyExpression");
}
var property = memberExpression.Member as PropertyInfo;
if (property == null)
{
throw new ArgumentException("The member access expression does not access a property.", "propertyExpression");
}
var getMethod = property.GetMethod;
if (getMethod.IsStatic)
{
throw new ArgumentException("The referenced property is a static property.", "propertyExpression");
}
return memberExpression.Member.Name;
}
}
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!