WPF：set属性不会在文本框值更改时触发

Question

我有一个绑定用户模型的EditUserViewModel。 在用户模型中，我具有公共属性，例如名字，姓氏，年龄等。

EditUserViewModel

public class EditUserViewModel : BindableBase
{
    private User _user;

    public EditUserViewModel(User user)
    {
        SaveCommand = new DelegateCommand(EditUser, CanSaveCommand);
        CancelCommand = new DelegateCommand(Cancel);
        User = user;
    }

    public User User
    {
        get{ return _user; }
        set
        {
            _user = value;
            OnPropertyChanged(() => User);
            SaveCommand.RaiseCanExecuteChanged();
        }
    }

    public DelegateCommand SaveCommand { get; set; }
    public ICommand CancelCommand { get; set; }

    public Func<bool> CanSaveCommand { get { return CanEditUser; } }

    private void EditUser()
    {
        Confirmed = true;
        FinishInteraction();
    }

    private bool CanEditUser()
    {
        if (string.IsNullOrEmpty(_user.Firstname) || _user.Firstname.Length < 3) return false;
        if (string.IsNullOrEmpty(_user.Lastname) || _user.Lastname.Length < 3) return false;

        return true;
    }
}

EditUserView

<UserControl x:Class="UserModule.Views.EditUserView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>

        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>

        <TextBlock FontWeight="Bold" Grid.Row="0" Grid.Column="0">First name:</TextBlock>
        <TextBox Grid.Row="0" Grid.Column="1" Text="{Binding Path=User.Firstname, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>

        <TextBlock FontWeight="Bold" Grid.Row="1" Grid.Column="0">First name:</TextBlock>
        <TextBox Grid.Row="1" Grid.Column="1" Text="{Binding Path=User.Lastname, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>

        <Button x:Name="OkButton" Grid.Row="2" Grid.Column="0" Command="{Binding SaveCommand}" Content="OK"/>
        <Button x:Name="CancelButton" Grid.Row="2" Grid.Column="1" Command="{Binding CancelCommand}" Content="Cancel"/>
    </Grid>

</UserControl>

用户

public User 
{
    public string Firstname  { get; set; }
    public string Lastname  { get; set; }
    public string Age  { get; set; }
}

但是，当我更改名字或姓氏时，User属性不会触发其设置程序。 但是，如果我在Viewmodel中具有Firstname和Lastname字符串属性，而不是使用User类属性，则当我在GUI中更改它们的值时，将触发它们的设置器。 我需要做一些特定的事情来使该类属性绑定起作用吗？

Answer 1

确保用户类实现了INotifyPropertyChanged

  public class User : INotifyPropertyChanged
{
    private String _firstname;
    public String Firstname
    {
        get
        {
            return _firstname;
        }

        set
        {
            if (_firstname == value)
            {
                return;
            }

            _firstname = value;
            OnPropertyChanged();
        }
    } 
    private String _lastName;
    public String LastName
    {
        get
        {
            return _lastName;
        }

        set
        {
            if (_lastName == value)
            {
                return;
            }

            _lastName = value;
            OnPropertyChanged();
        }
    }
    public ObservableCollection<DataGridEntry> DataGridEntries { get; set; }

    public event PropertyChangedEventHandler PropertyChanged;

    [NotifyPropertyChangedInvocator]
    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }
}

Answer 2

    public class User : BindableBase
    {
       private string _firstName;
       private string _lastName;
       private string _age;

    public string Firstname  
    { 
      get{ return _firstName;} 
      set
      {
           _firstName = value;
           OnPropertyChanged(() => Firstname);
      }
    }

    public string LastName
    { 
      get{ return _lastName;} 
      set
      {
           _lastName = value;
           OnPropertyChanged(() => LastName);
      }
    }

    public string Age
    { 
      get{ return _age;} 
      set
      {
           _age = value;
           OnPropertyChanged(() => Age);
      }
    }
}

Answer 3

在类User中实现INotifiyPropertyChanged本身应允许通过ViewModel进行绑定。

http://msdn.microsoft.com/fr-fr/library/system.componentmodel.inotifypropertychanged%28v=vs.110%29.aspx