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

我建议使用ReactiveProperty。 这是除了Fody之外最短的方法。

public class Data : INotifyPropertyChanged
{
    // boiler-plate
    ...
    // props
    private string name;
    public string Name
    {
        get { return name; }
        set { SetField(ref name, value, "Name"); }
    }
}

而不是

public class Data
{
    // Don't need boiler-plate and INotifyPropertyChanged

    // props
    public ReactiveProperty<string> Name { get; } = new ReactiveProperty<string>();
}

(文档)

其他回答

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!

反射:利用反射的思想:

class ViewModelBase : INotifyPropertyChanged {

    public event PropertyChangedEventHandler PropertyChanged;

    bool Notify<T>(MethodBase mb, ref T oldValue, T newValue) {

        // Get Name of Property
        string name = mb.Name.Substring(4);

        // Detect Change
        bool changed = EqualityComparer<T>.Default.Equals(oldValue, newValue);

        // Return if no change
        if (!changed) return false;

        // Update value
        oldValue = newValue;

        // Raise Event
        if (PropertyChanged != null) {
            PropertyChanged(this, new PropertyChangedEventArgs(name));
        }//if

        // Notify caller of change
        return true;

    }//method

    string name;

    public string Name {
        get { return name; }
        set {
            Notify(MethodInfo.GetCurrentMethod(), ref this.name, value);
        }
    }//method

}//class

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));
    }
}

这就是大规模的过度工程。这比仅仅以正确的方式进行要复杂得多,而且几乎没有任何好处。如果你的IDE支持代码片段(Visual Studio/MonoDevelop支持),那么你可以让这个实现变得非常简单。你需要输入的只是属性的类型和属性名。额外的三行代码将自动生成。

它是2022。现在有了官方的解决方案。

使用Microsoft MVVM工具包中的MVVM源生成器。

This

[ObservableProperty]
private string? name;

将生成:

private string? name;

public string? Name
{
    get => name;
    set
    {
        if (!EqualityComparer<string?>.Default.Equals(name, value))
        {
            OnNameChanging(value);
            OnPropertyChanging();
            name = value;
            OnNameChanged(value);
            OnPropertyChanged();
        }
    }
}

// Property changing / changed listener
partial void OnNameChanging(string? value);
partial void OnNameChanged(string? value);

protected void OnPropertyChanging([CallerMemberName] string? propertyName = null)
{
    PropertyChanging?.Invoke(this, new PropertyChangingEventArgs(propertyName));
}

protected void OnPropertyChanged([CallerMemberName] string? propertyName = null)
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}

它支持。net标准2.0和。net >= 5.0。