이에 대해 DependencyProperty를 사용할 수 있습니까?

Question

나는 ObservableCollection이고 Students입니다. 각 학생에게는 Grade 속성이 있습니다. 단추를 누르거나 타이머를 만들지 않고도 모든 학생의 AverageGrade 속성을 사용하고 싶습니다. 이 읽기 ​​전용 AverageGrade 속성에 DependencyProperty을 어떻게 사용합니까? 당신이 정상 VM 속성 걸릴처럼 보일 것을 위해 DP를 원하는 이유

Student.cs

using System.ComponentModel; 
using System.Windows; 
using System; 

namespace WpfApplication17.Models 
{ 
    class Student : INotifyPropertyChanged 
    { 
     #region Constructors 

     public Student(string firstName, string lastName, double grade) 
           { 
      this.FirstName = firstName; 
      this.LastName = lastName; 
       this.Grade = grade; 
     } 

         #endregion 

     #region Properties 

       private string _firstName; 

     public string FirstName 
     { 
      get { return _firstName; } 
      set 
      { 
       _firstName = value; 
       OnPropertyChanged("FirstName"); 
      } 
     } 

     private string _lastName; 

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

     private double _grade; 

     public double Grade 
     { 
     get { return _grade; } 
     set 
     { 
      _grade = value; 
      OnPropertyChanged("Grade"); 
     } 
    } 

    #endregion 

    #region PropertyChanged 

    public event PropertyChangedEventHandler PropertyChanged; 

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

    #endregion 
} 

}

MainWindowViewModel

using WpfApplication17.ViewModel; 
using System.Collections.ObjectModel; 
using WpfApplication17.Models; 

namespace WpfApplication17.ViewModels 
{ 
    class MainWindowViewModel : ViewModelBase 
    { 
     #region Constructors 

     public MainWindowViewModel() 
     { 
      Students = new ObservableCollection<Student>(); 
      Students.Add(new Student("Frank", "Sinatra", 7)); 
      Students.Add(new Student("Bart", "Simpson", 6)); 
     } 

     #endregion 

     #region Properties 

     private ObservableCollection<Student> _students; 

     public ObservableCollection<Student> Students 
     { 
      get { return _students; } 
      set 
      { 
       _students = value; 
       OnPropertyChanged("Students"); 
      } 
     } 

     public double AverageGrade 
     { 
      get { return GetAverageGrade(); } 
     } 

     public double GetAverageGrade() 
     { 
      double sum = 0; 

      foreach (Student s in Students) 
       sum += s.Grade; 

      return sum/(double)Students.Count; 
     } 

     #endregion 
    } 
} 

MainWindow.xaml

<Window x:Class="WpfApplication17.MainWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     Title="MainWindow" Height="350" Width="525"> 
    <StackPanel Orientation="Horizontal"> 
     <DataGrid ItemsSource="{Binding Students}" /> 
     <Label Content="Average Grade:" /> 
     <Label Content="{Binding AverageGrade}" /> 
    </StackPanel> 
</Window> 

Answer 1

관심의 대상 입니다. 새로운 학생이 추가되거나 기존 학생의 성적이 변경 될 때마다 AverageGrade를 업데이트해야합니다.

어쩌면이 방법을 시도해보십시오

class MainWindowViewModel 
{ 
    #region Constructors 

    public MainWindowViewModel() 
    { 
     Students = new ObservableCollection<Student>(); 
     Students.Add(new Student("Frank", "Sinatra", 7)); 
     Students.Add(new Student("Bart", "Simpson", 6)); 

     Students.CollectionChanged += (s, e) => AverageGrade = this.GetAverageGrade(); 

     foreach (var student in Students) 
     { 
      student.PropertyChanged += OnStudentPropertyChanged; 
     } 

     AverageGrade = this.GetAverageGrade(); 
    } 

    private void OnStudentPropertyChanged(object sender, PropertyChangedEventArgs e) 
    { 
     if (e.PropertyName == "Grade") 
     { 
      AverageGrade = this.GetAverageGrade(); 
     } 
    } 

    #endregion 

    #region Properties 

    private ObservableCollection<Student> _students; 

    public ObservableCollection<Student> Students 
    { 
     get { return _students; } 
     set 
     { 
      _students = value; 
      OnPropertyChanged("Students"); 
     } 
    } 

    private double average; 
    public double AverageGrade 
    { 
     get 
     { 
      return this.average; 
     } 
     set 
     { 
      this.average = value; 
      OnPropertyChanged("AverageGrade"); 
     } 
    } 

    public double GetAverageGrade() 
    { 
     return this.Students.Sum(s => s.Grade)/Students.Count; 
    } 

    #endregion 

    public event PropertyChangedEventHandler PropertyChanged; 

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