帶實體框架的WPF MVVM？

Question

我正在用Entity Framework 4在VS2010 .NET4.0中構建一個簡單的mvvm WPF應用程序。我是一個只有1年編程經驗的WPF初學者。嘗試將我的XAML中的數據網格綁定到實體框架模型。我的View Model中有一個可觀察的集合，但似乎無法讀取數據？

我有一個包含在項目中的實體框架.edmx，它包含一個帶有主ID的單個「tbCountrys」表。

這裏是剛剛宣佈了一些變量/與我的表列的屬性和實現INotifyPropertyChanged我的模型類：

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.ComponentModel; 

namespace Entity_MVVM 
{ 
public class CountrysModel : INotifyPropertyChanged 
{ 
    #region variables 

    private string _CountryId; 
    private string _ShortName; 
    private string _LongName; 

    # endregion 

    # region Properties 

    public string CountryId 
    { 
     get { return _CountryId; } 
     set { _CountryId = value; 
       OnPropertyChanged("CountryId"); 
     } 
    } 

    public string ShortName 
    { 
     get { return _ShortName; } 
     set 
     { 
      _ShortName = value; 
      OnPropertyChanged("ShortName"); 
     } 
    } 

    public string LongName 
    { 
     get { return _LongName; } 
     set 
     { 
      _LongName = value; 
      OnPropertyChanged("LongName"); 
     } 
    } 

    #endregion 

    # region INotifyPropertyChanged 

    public event PropertyChangedEventHandler PropertyChanged; 

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

    # endregion 
    } 
} 

我的視圖模型也實現INotifyPropertyChanged，宣稱可觀察集合來存儲我的查詢結果，有一個LoadGrid（）方法，它應該用EntityConnection查詢我的表並填充Observable集合。這似乎沒有工作？

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Windows.Data; 
using System.Collections.ObjectModel; 
using System.ComponentModel; 
using System.Data.EntityClient; 
using System.Data; 
using System.Windows; 
using System.Collections; 


namespace Entity_MVVM 
{ 
    public class CountrysViewModel : INotifyPropertyChanged 
    { 
    #region Constructor 

    public CountrysViewModel() 
    { 
     LoadGrid(); 
    } 

    # endregion 

    # region INotifyPropertyChanged 

    public event PropertyChangedEventHandler PropertyChanged; 

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

    # endregion 

    # region ObservableCollection 

    private ObservableCollection<CountrysModel> _CountrysModelObservableList = new ObservableCollection<CountrysModel>(); 
    public ObservableCollection<CountrysModel> CountrysModelObservableList 
    { 
     get { return _CountrysModelObservableList; } 
     set 
     { 
      _CountrysModelObservableList = value; 
      OnPropertyChanged("CountrysModelObservableList"); 
     } 
    } 

    # endregion 

    # region Properties 

    private CountrysModel _CountrysModelView; 
    public CountrysModel CountrysModelView 
    { 
     get { return _CountrysModelView; } 
     set 
     { 
      _CountrysModelView = value; 
      OnPropertyChanged("CountrysModel"); 
     } 
    } 

    # endregion 

    # region LoadGrid Method 

    public void LoadGrid() 
    { 
     LDBEntities db = new LDBEntities(); 
     using (var conn = new EntityConnection("name=LDBEntities")) 
     { 
      conn.Open(); 
      EntityCommand cmd = conn.CreateCommand(); 
      cmd.CommandText = "SELECT * FROM LDBEntities.tbCountrys"; 

      try 
      { 
       EntityDataReader rdr = cmd.ExecuteReader(CommandBehavior.SequentialAccess | CommandBehavior.CloseConnection); 

       _CountrysModelObservableList.Clear(); 

       while (rdr.Read()) 
       { 
        var cCountryId = rdr["CountryId"].ToString(); 
        var cShortName = rdr["shortName"].ToString(); 
        var cLongName = rdr["longName"].ToString(); 

        _CountrysModelView = new CountrysModel() 
        { 
         CountryId = cCountryId, 
         ShortName = cShortName, 
         LongName = cLongName 
        }; 

        _CountrysModelObservableList.Add(_CountrysModelView); 
       } 
      } 
      catch 
      { 
       MessageBox.Show(string.Format("Can't read in data!")); 
      } 
     } 

    #endregion 

     } 
    } 
    } 

最後，我的XAML視圖：

<Window x:Class="Entity_MVVM.MainWindow" 
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
     xmlns:vm="clr-namespace:Entity_MVVM" 
     Title="MainWindow" Height="350" Width="525" 
     DataContext="{DynamicResource MyViewModel}"> 
    <Window.Resources> 
     <vm:CountrysViewModel x:Key="MyViewModel"/> 
    </Window.Resources> 
    <Grid> 
     <DataGrid Width="400" Height="127" Name="grdPublications" ItemsSource="{Binding Path=CountrysModelObservableList}"> 
     </DataGrid> 
    </Grid> 
</Window> 

當我調試的代碼，在我的視圖模型try塊是我從我的視圖模型的構造函數調用LoadGrid（）方法未執行並引發catch異常。讀取數據的while循環從不運行，因爲它在聲明EntityDataReader對象後退出。也許有一些不太正確的查詢語法？

任何幫助將是最受讚賞的，因爲我無法找到許多使用實體框架與MVVM的在線示例。由於

而且，得到這個例外在XAML，不能創建我的視圖模型的實例。連接字符串在App.config中是正確的，所以不知道是什麼導致它...

Answer 1

你連接字符串看起來確實錯了。 代碼失敗在EntityConnection構造

at System.Data.EntityClient.EntityConnection.ctor(String connectionString) 

所以這是這一行：

new EntityConnection("name=LDBEntities") 

什麼樣的連接字符串的是"name=LDBEntities"？

我想你已經忘記從你的資源文件中獲取連接字符串。

new EntityConnection(SomeResource.LDBEntities)