C# 使用NotifyPropertyWeaver时如何获取OnPropertyChange事件？

我使用NotifyPropertyWeaverMsBuildTask为自动属性处理NotifyPropertyChanged。我知道OnPropertyChanged（）方法在属性值更改时会上升。但当这个方法被调用时，属性的值被改变，旧的值丢失。有没有办法得到旧的价值

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tanx.

INotifyPropertyChanged

不提供获取属性先前值的方法；您必须实现自己的功能。

INotifyPropertyChanged

不提供获取属性先前值的方法；您必须实现自己的。

如果您想在

OnPropertyChanged

中使用旧值，那么就这样编写它

public void OnPropertyChanged(string propertyName, object before, object after)

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public string Name { get; set; }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

如果你的代码是这样的

public void OnPropertyChanged(string propertyName, object before, object after)

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public string Name { get; set; }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

这将被注入

public class Person : INotifyPropertyChanged
{
    private string name;

    public event PropertyChangedEventHandler PropertyChanged;

    public string Name
    {
        get { return name; }
        set
        {
            object before = Name;
            name = value;
            OnPropertyChanged("Name", before, Name);
        }
    }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {            
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

这里有更多信息

---

这符合您的要求吗？

如果您想在

OnPropertyChanged

中使用旧值，请这样编写

public void OnPropertyChanged(string propertyName, object before, object after)

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public string Name { get; set; }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

如果你的代码是这样的

public void OnPropertyChanged(string propertyName, object before, object after)

public class Person : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    public string Name { get; set; }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

这将被注入

public class Person : INotifyPropertyChanged
{
    private string name;

    public event PropertyChangedEventHandler PropertyChanged;

    public string Name
    {
        get { return name; }
        set
        {
            object before = Name;
            name = value;
            OnPropertyChanged("Name", before, Name);
        }
    }

    public void OnPropertyChanged(string propertyName, object before, object after)
    {            
        // do something with before/after
        var propertyChanged = PropertyChanged;
        if (propertyChanged != null)
        {
            propertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

这里有更多信息

---

这符合您的要求吗？

您想将旧值用于什么？您想将旧值用于什么？