Winforms包含列表的數據綁定對象<T>

Question

我遇到了一個我知道的情況一定很常見的問題，所以我希望解決方案很簡單。我有一個對象，其中包含一個對象列表<>。它還有一些屬性反映了列表<>中的對象的集合數據（實際上是綁定列表<>因此我可以綁定到它）。在我的表單中，我有一個DataGridView用於List，還有一些其他字段用於聚合數據。我無法弄清楚如何在DataGridView中的值發生更改時觸發刷新聚合數據。

我試着在列表中的對象的屬性發生更改時引發PropertyChanged事件，但似乎沒有刷新聚合數據的顯示。如果我訪問一個聚合屬性（例如，將其顯示在消息框中），則會刷新主窗體上的文本框。

下面是一些簡單的代碼來說明我想要做的事：

namespace WindowsFormsApplication1 { 
public class Person { 

    public int Age { 
     get; 
     set; 
    } 

    public String Name { 
     get; 
     set; 
    } 
} 

public class Roster : INotifyPropertyChanged { 

    public BindingList<Person> People { 
     get; 
     set; 
    } 

    public Roster() { 
     People = new BindingList<Person>(); 
    } 

    private int totalage; 
    public int TotalAge { 
     get { 
      calcAges(); 
      return totalage; 
     } 
     set { 
      totalage = value; 
      NotifyPropertyChanged("TotalAge"); 
     } 
    } 

    private void calcAges() { 
     int total = 0; 
     foreach (Person p in People) { 
      total += p.Age; 
     } 
     TotalAge = total; 
    } 

    #region INotifyPropertyChanged Members 
    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged (String info) { 
     if (PropertyChanged != null) { 
      PropertyChanged(this, new PropertyChangedEventArgs(info)); 
     } 
    } 
    #endregion 
} 
} 

Answer 1

calcAges方法和TotalAge屬性看起來非常可疑。

首先，TotalAge應該是隻讀的。如果你允許它是公開的和可寫的，那麼改變組成這個時代的組件的邏輯是什麼？

其次，每次獲得該值時，您都會觸發PropertyChanged事件，這並不好。

你Roster類應該是這樣的：

public class Roster : INotifyPropertyChanged { 

    public Roster() 
    { 
     // Set the binding list, this triggers the appropriate 
     // event binding which would be gotten if the BindingList 
     // was set on assignment. 
     People = new BindingList<Person>(); 
    } 

    // The list of people. 
    BindingList<Person> people = null; 

    public BindingList<Person> People 
    { 
     get 
     { 
      return people; 
     } 
     set 
     { 
      // If there is a list, then remove the delegate. 
      if (people != null) 
      { 
       // Remove the delegate. 
       people.ListChanged -= OnListChanged; 
      } 

      /* Perform error check here */ 
      people = value; 

      // Bind to the ListChangedEvent. 
      // Use lambda syntax if LINQ is available. 
      people.ListChanged += OnListChanged; 

      // Technically, the People property changed, so that 
      // property changed event should be fired. 
      NotifyPropertyChanged("People"); 

      // Calculate the total age now, since the 
      // whole list was reassigned. 
      CalculateTotalAge(); 
     } 
    } 

    private void OnListChanged(object sender, ListChangedEventArgs e) 
    { 
     // Just calculate the total age. 
     CalculateTotalAge(); 
    } 

    private void CalculateTotalAge() 
    { 
     // Store the old total age. 
     int oldTotalAge = totalage; 

     // If you can use LINQ, change this to: 
     // totalage = people.Sum(p => p.Age); 

     // Set the total age to 0. 
     totalage = 0; 

     // Sum. 
     foreach (Person p in People) { 
      totalage += p.Age; 
     } 

     // If the total age has changed, then fire the event. 
     if (totalage != oldTotalAge) 
     { 
      // Fire the property notify changed event. 
      NotifyPropertyChanged("TotalAge"); 
     } 
    } 

    private int totalage = 0; 

    public int TotalAge 
    { 
     get 
     { 
      return totalage; 
     } 
    } 
    public event PropertyChangedEventHandler PropertyChanged; 

    private void NotifyPropertyChanged (String info) { 
     if (PropertyChanged != null) { 
      PropertyChanged(this, new PropertyChangedEventArgs(info)); 
     } 
    } 
} 

現在，當列表中的項目性質發生改變，父對象將觸發屬性更改事件，和任何綁定到它應該隨之改變。

Answer 2

我相信你可能會尋找這樣的事情

ITypedList

而且ITypedList引線的Google Search你到幾個漂亮的博客如何實施。

當我使用ORM時，我通常必須爲這些好的數據網格綁定和表示做些操作。