如何在WPF視圖模型中使用關係表

Question

我正在構建一個N層WPF應用程序。我想要零代碼隱藏。

比方說，我有3個標準化的相關表來記錄銷售交易。

交易：

TRANSACTIONID， 項目Id， 供應商ID， 價格

供應商：

供應商ID， SupplierName

ITEMS：

ItemId， ItemName。

對於每個表我有一個反映字段的基類。然後是根據需要填充基礎對象集合的數據層。

我想有一個展示的所有交易的列表頁面上的列表框，每行1個交易，行應該是這個樣子......

"Trainers FootLocker €99" 

"Trousers TopShop  €45" 

"Coat  TopShop  €49" 

如果我使用

<ListBox 
    ItemsSource="{Binding Path=Transactions}" 
    SelectedItem="{Binding CurrentTransaction}" 

然後我最終得到來自Transactions表的ID行，而不是來自Items和Suppliers表的Name值。

鑑於我有其他表填充只有ID的事務的集合，填充列表框的最佳方法是什麼？

我想知道的一件事是，如果我的事務基礎對象包含項目項填充那裏而不是int ItemId？

交易基本型號：

using System; 
using System.ComponentModel; 
using PFT; 
using PFT.Data; 

namespace PFT.Base 
{ 



    public class Transaction : INotifyPropertyChanged 
    { 

     public int Id { get; set; } 

     private int _itemId; 
     public int ItemId 
     { 
      get { return _itemId; } 
      set { 
       _itemId = value; 

       ItemData id = new ItemData(); 
       this.Item = id.Select(value); 

       NotifyPropertyChanged("ItemId"); 
      } 
     } 

     private Item _item; 

     public Item Item 
     { 
      get { return _item; } 
      set { _item = value; } 
     } 


     private float _price; 
     public float Price 
     { 
      get { return _price; } 
      set { 
       _price = value; 
       NotifyPropertyChanged("Price"); 
      } 
     } 

     private DateTime _date; 
     public DateTime Date 
     { 
      get { return _date; } 
      set { 
       _date = value; 
       NotifyPropertyChanged("Date"); 
      } 
     } 


     private string _comment; 
     public string Comment 
     { 
      get { return _comment; } 
      set 
      { 
       _comment = value; 
       NotifyPropertyChanged("Comment"); 
      } 
     } 

     private int _traderId; 
     public int TraderId 
     { 
      get { return _traderId; } 
      set 
      { 
       _traderId = value; 
       NotifyPropertyChanged("TraderId"); 
      } 
     } 

     private Trader _trader; 

     public Trader Trader 
     { 
      get { return _trader; } 
      set { _trader = value; 

      TraderData t = new TraderData(); 
      this.Trader = t.Select(value); 
      } 
     } 


     private string _insertType; 
     /// <summary> 
     /// A - Auto, M - Manual, V - Verified 
     /// </summary> 
     public string InsertType 
     { 
      get { return _insertType; } 
      set { _insertType = value; 
      NotifyPropertyChanged("InsertType"); 
      } 
     } 



     public event PropertyChangedEventHandler PropertyChanged; 
     // This method is called by the Set accessor of each property. 
     // The CallerMemberName attribute that is applied to the optional propertyName 
     // parameter causes the property name of the caller to be substituted as an argument. 
     //private void NotifyPropertyChanged([CallerMemberName] String propertyName = "") 
     private void NotifyPropertyChanged(String propertyName = "") 
     { 
      if (PropertyChanged != null) 
      { 
       PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); 
      } 
     } 
    } 

項基礎類

using System.ComponentModel; 

namespace PFT.Base 
{ 
    public class Item : INotifyPropertyChanged 
    { 
     private int _id; 

     public int Id 
     { 
      get { return _id; } 
      set { _id = value; 
      NotifyPropertyChanged("Id"); 
      } 
     } 



     private string _name; 

     public string Name 
     { 
      get { return _name; } 
      set { _name = value; 
      NotifyPropertyChanged("Name"); 
      } 
     } 


     private string _description; 

     public string Description 
     { 
      get { return _description; } 
      set { _description = value; 
      NotifyPropertyChanged("Description"); 
      } 
     } 


     private float _defaultPrice; 

     public float DefaultPrice 
     { 
      get { return _defaultPrice; } 
      set { _defaultPrice = value; 
      NotifyPropertyChanged("DefaultPrice"); 
      } 
     } 

     private bool _isIncome; 

     public bool IsIncome 
     { 
      get { return _isIncome; } 
      set { _isIncome = value; 
      NotifyPropertyChanged("IsIncome"); 
      } 
     } 

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

    } 
} 

Answer 1

你用的ViewModels做到這一點的方法是給Transaction一個Supplier財產和財產Item。這些屬性將引用自己集合中實際的Item和Supplier對象。如果每次交易的關係爲一個ItemID和一個SupplierID，則這是等價的對象。如果交易能夠多條記錄與同一交易ID和不同的供應商或產品標識，並Transaction需要收藏Item和Supplier。我們也可以在WPF中這樣做，但是它會比下面的簡單示例花費更多的尖括號。

你會設定，當您從數據庫中獲取您的項目（但你這樣做），或也許實體框架可以爲你做的。

真正簡單的列表框顯示項目名稱：添加DisplayMemberPath。

<ListBox 
    ItemsSource="{Binding Transactions}" 
    SelectedItem="{Binding CurrentTransaction}" 
    DisplayMemberPath="Item.Name" 
    /> 

更復雜：

<ListBox 
    ItemsSource="{Binding Transactions}" 
    SelectedItem="{Binding CurrentTransaction}" 
    > 
    <ListBox.ItemTemplate> 
     <DataTemplate> 
      <TextBlock> 
       <Run Text="{Binding Item.Name, Mode=OneWay}" /> 
       <Run Text=" - " /> 
       <Run Text="{Binding Supplier.Name, Mode=OneWay}" /> 
       <Run Text=" " /> 
       <Run Text="{Binding Price, Mode=OneWay, StringFormat=c}" /> 
      </TextBlock> 
     </DataTemplate> 
    </ListBox.ItemTemplate> 
</ListBox> 

你也可以尋找到一個圓柱控制像ListView或DataGrid。

稍微偏離主題，零代碼隱退有點極端。這是最後的手段，而不是第三軌。最小的代碼隱藏是一個合理的總體原則。不要爲了避免它而瘋狂;這是有原因的。

UPDATE

public class Transaction : INotifyPropertyChanged 
{ 
    // ... stuff ... 

    public Item Item 
    { 
     get { return _item; } 
     set { 
      _item = value; 
      // If this property is ever set outside the Transaction 
      // constructor, you ABSOLUTELY MUST raise PropertyChanged here. 
      // Otherwise, make the setter private. But just raise the event. 

      // This has nothing whatsoever to do with when or whether the Item 
      // class raises PropertyChanged, because this is not a property of the 
      // Item class. This is a property of Transaction. 

      NotifyPropertyChanged("Item"); 
     } 
    } 

    // ... more stuff ...