c# - MVVM跟踪 View 模型中的问题

Question

我的要求是跟踪数据上下文中发生的更改，并且当属性更改时，我已将新的 View 模型添加为历史记录项。第一次它正常工作时，进行第二次更改时，第二个也反射(reflect)在历史记录的已添加项中。我是做错了请帮忙。

public partial class MainWindow : Window
{
    private List<Employee> history;

    public List<Employee> History
    {
        get { return history; }
        set { history = value; }
    }

    public MainWindow()
    {
        InitializeComponent();
        History = new List<Employee>();
        this.DataContext = new Employee();
        if (DataContext != null)
        {
            this.DataContextChanged += new DependencyPropertyChangedEventHandler(MainWindow_DataContextChanged);
            (this.DataContext as Employee).PropertyChanged += new PropertyChangedEventHandler(MainWindow_PropertyChanged);
        }
    }

    private void MainWindow_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        History.Add((Employee)this.DataContext);
    }

    private void MainWindow_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
    }

    private void button1_Click(object sender, RoutedEventArgs e)
    {
    }
}

public class Employee : INotifyPropertyChanged
{
    private List<Employee> history;

    public List<Employee> History
    {
        get { return history; }
        set { history = value; }
    }

    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; RaisePropertyChanged("Name"); }
    }

    private string ph;

    public string PH
    {
        get { return ph; }
        set { ph = value; RaisePropertyChanged("PH"); }
    }

    private DateTime dob;

    public DateTime DOB
    {
        get { return dob; }
        set { dob = value; RaisePropertyChanged("DOB"); }
    }

    private int age;

    public int Age
    {
        get { return age; }
        set { age = value; RaisePropertyChanged("Age"); }
    }

    public Employee()
    {
        History = new List<Employee>();
        Name = "MKumar";
        Age = 10;
        DOB = new DateTime(2004, 7, 8);
        PH = "999999999";
        PropertyChanged += new PropertyChangedEventHandler(Employee_PropertyChanged);
    }

    private void Employee_PropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        History.Add(this);
        //throw new NotImplementedException();
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void RaisePropertyChanged(string name)
    {
        if (PropertyChanged != null)
            this.PropertyChanged(this, new PropertyChangedEventArgs(name));
    }
}

谢谢

Answer 1

这很正常，因为您的对象是reference type。您应该制作一个deep copy，以反射(reflect)历史记录列表中的更改

尝试这样的事情

private void Employee_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    var  empCloned = DeepClone(this); 
    History.Add(empCloned);
    //throw new NotImplementedException();
}

深度复制

private T DeepClone<T>(T obj)
{
    using (var ms = new MemoryStream())
    {
        var formatter = new BinaryFormatter();
        formatter.Serialize(ms, obj);
        ms.Position = 0;

        return (T) formatter.Deserialize(ms);
    }
}