WPF MVVM 双向更新

Question

我正在尝试使用此示例设置有效的双向更新。

这些是相关的代码片段：

XAML：

<Button Click="clkInit">Initialize</Button>
<Button Click="clkStudent">Add student</Button>
<Button Click="clkChangeStudent">Change students</Button>
(...)
<TabControl Name="tabControl1" ItemsSource="{Binding StudentViewModels}" >
   <TabControl.ItemTemplate>
      <DataTemplate>
         <TextBlock Text="{Binding Path=StudentFirstName}" />
      </DataTemplate>
   </TabControl.ItemTemplate>
   <TabControl.ContentTemplate>                
      <DataTemplate>
         <Grid>
            <Label Content="First Name" Name="label1" />
            <TextBox Name="textBoxFirstName" Text="{Binding Path=StudentFirstName}" />
            <Label Content="Last Name" Name="label2" />
            <TextBox Name="textBoxLastName" Text ="{Binding Path=StudentLastName}" />
         </Grid>                    
      </DataTemplate>
   </TabControl.ContentTemplate>
</TabControl>

主窗口：

public partial class MainWindow : Window
{
    internal MainWindowViewModel myMWVM;
    public MainWindow()
    {
       InitializeComponent();
    }

    private void clkInit(object sender, RoutedEventArgs e)
    {
       myMWVM= new MainWindowViewModel();
       DataContext = myMWVM;
    }
    private void clkStudent(object sender, RoutedEventArgs e)
    {
       myMWVM.StudentViewModels.Add(new StudentViewModel());
    }
    // For testing - call a function out of the student class to make changes there
    private void clkChangeStudent(object sender, RoutedEventArgs e)
    {
       for (Int32 i = 0; i < test.StudentViewModels.Count; i++)
       {
           myMWVM.StudentViewModels.ElementAt((int)i).changeStudent();
       }
    }
}

主要观点：

class MainWindowViewModel : INotifyPropertyChanged
{
   ObservableCollection<StudentViewModel> _studentViewModels = 
        new ObservableCollection<StudentViewModel>();

   // Collection for WPF.
   public ObservableCollection<StudentViewModel> StudentViewModels
   {
      get { return _studentViewModels; }
   }

   // Constructor. Add two stude
   public MainWindowViewModel()
   {
      _studentViewModels.Add(new StudentViewModel());
      _studentViewModels.Add(new StudentViewModel());
   }

   // Property change.
   public event PropertyChangedEventHandler PropertyChanged;
   private void OnPropertyChanged(string propertyName)
   {
      if (PropertyChanged != null)
      {
         PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
      }
   }
}

学生观点：

class StudentViewModel : INotifyPropertyChanged
{
   Lazy<Student> _model;

   string _studentFirstName;
   public string StudentFirstName
   {
      get { return _studentFirstName; }
      set
      {
         if (_studentFirstName != value)
         {
            _studentFirstName = value;
            _model.Value.StudentFirstName = value;
            OnPropertyChanged("StudentFirstName");
         }
      }
   }

   string _studentLastName;
   public string StudentLastName
   {
      get { return _studentLastName; }
      set
      {
         if (_studentLastName != value)
         {
            _studentLastName = value;
            _model.Value.StudentLastName = value;
            OnPropertyChanged("StudentLastName");
         }
      }
   }

   public void changeStudent()
   {
      _model.Value.changeStudent();
   }


   public StudentViewModel()
   {
      _studentFirstName = "Default";
      _model = new Lazy<Student>(() => new Student());
   }


   public event PropertyChangedEventHandler PropertyChanged;
   private void OnPropertyChanged(string propertyName)
   {
      if (PropertyChanged != null)
      {
         PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
      }
   }
}

学生：

class Student
{
   public string StudentFirstName { get; set; }
   public string StudentLastName { get; set; }

   public Student()
   {
      MessageBox.Show("Student constructor called");
   }
   public Student(string nm)
   {
      StudentLastName = nm;
   }
   public void changeStudent()
   {
      StudentLastName = "McDonald";
   }
}

如果您读到这里，我已经感谢您 :) 尽管如此，通过调用“clkChangeStudent”，我没有看到文本框中的更改。我猜是因为我没有调用StudentViewModel 的set-method。我正在做的项目有点复杂，很多事情发生在班级（这里是学生）本身。

如何通过学生类本身的设置值获取文本框更新？

Answer 1

您的实际代码显然不会通知界面的更改。原因很简单。您更改学生姓名的方法位于 Student 模型中，并且该模型未实现 INotifyPropertyChanged。

根据一个问题，有两种解决方案可以解决此问题，changeStudent() 方法是否必须坚持对象模型，也就是说，您的要求是否允许您将 changeStudent() 方法移动到视图模型？

如果是，那么，第一个解决方案，只需从模型中删除 changeStudent 方法并将其移动到视图模型，如下所示：

class StudentViewModel : INotifyPropertyChanged
{
    ...

    public void changeStudent()
    {
        this.StudentLastName = "McDonald";
    }
}

在另一种情况下，第二种解决方案，您必须在模型属性更改时引发事件，然后让您的视图模型订阅这些更改。您可以在模型中像这样继续：

class Student : INotifyPropertyChanged
{
    ...

    private string studentLastName;

    public string StudentLastName
    {
        get
        {
            return this.studentLastName;
        }

        set
        {
            if(this.studentLastname != value)
            {
                this.studentLastName = value;
                this.OnPropertyChanged("StudentLastName");
            }
        }
    }
}

对于视图模型：

class StudentViewModel : INotifyPropertyChanged
{
    ...

    public StudentViewModel(Student model)
    {
        this._model = model;

        this._model.PropertyChanged += (sender, e) =>
        {
            if(e.PropertyName == "StudentLastName")
            {
                this.OnPropertyChanged("StudentLastName");
            }
        };
    }
}

两种解决方案都有效。真正重要的是，您了解您的代码在值更改时明确需要通知接口。