ComboBox wpf綁定列表已更改

Question

我對ComboBox有關於在重新加載列表上綁定選定項目的問題。

class Model : ViewModelBase 
{ 
    /// <summary> 
    /// The <see cref="Title" /> property's name. 
    /// </summary> 
    public const string TitlePropertyName = "Title"; 

    private string _title = ""; 

    /// <summary> 
    /// Sets and gets the Title property. 
    /// Changes to that property's value raise the PropertyChanged event. 
    /// </summary> 
    public string Title 
    { 
     get 
     { 
      return _title; 
     } 

     set 
     { 
      if (_title == value) 
      { 
       return; 
      } 

      RaisePropertyChanging(TitlePropertyName); 
      _title = value; 
      RaisePropertyChanged(TitlePropertyName); 
     } 
    } 

    /// <summary> 
    /// The <see cref="Id" /> property's name. 
    /// </summary> 
    public const string idPropertyName = "Id"; 

    private int _myId = 0; 

    /// <summary> 
    /// Sets and gets the id property. 
    /// Changes to that property's value raise the PropertyChanged event. 
    /// </summary> 
    public int Id 
    { 
     get 
     { 
      return _myId; 
     } 

     set 
     { 
      if (_myId == value) 
      { 
       return; 
      } 

      RaisePropertyChanging(idPropertyName); 
      _myId = value; 
      RaisePropertyChanged(idPropertyName); 
     } 
    } 
} 

綁定視圖模型：

class MainViewModel : ViewModelBase 
{ 
    public MainViewModel() 
    { 

     PopulateCommand = new RelayCommand(() => 
     { 
      Populate(); 
     }); 

     SetCommand = new RelayCommand(() => 
     { 
      Id = 3; 
     }); 
    } 

    public void Populate() 
    { 
     MyList = new ObservableCollection<Model>(){ 
      new Model(){ 
       Id = 1, 
       Title = "numer1" 
      }, 
      new Model(){ 
       Id = 2, 
       Title = "numer2" 
      }, 
      new Model(){ 
       Id = 3, 
       Title = "numer3" 
      }, 
      new Model(){ 
       Id = 4, 
       Title = "numer4" 
      }, 
     }; 
    } 

    public RelayCommand PopulateCommand { get; private set; } 
    public RelayCommand SetCommand { get; private set; } 

    /// <summary> 
    /// The <see cref="MyList" /> property's name. 
    /// </summary> 
    public const string MyListPropertyName = "MyList"; 

    private ObservableCollection<Model> _myList = null; 

    /// <summary> 
    /// Sets and gets the MyList property. 
    /// Changes to that property's value raise the PropertyChanged event. 
    /// </summary> 
    public ObservableCollection<Model> MyList 
    { 
     get 
     { 
      return _myList; 
     } 

     set 
     { 
      if (_myList == value) 
      { 
       return; 
      } 

      RaisePropertyChanging(MyListPropertyName); 
      _myList = value; 
      RaisePropertyChanged(MyListPropertyName); 
     } 
    } 

    /// <summary> 
    /// The <see cref="Id" /> property's name. 
    /// </summary> 
    public const string IdPropertyName = "Id"; 

    private int _id = 0; 

    /// <summary> 
    /// Sets and gets the Id property. 
    /// Changes to that property's value raise the PropertyChanged event. 
    /// </summary> 
    public int Id 
    { 
     get 
     { 
      return _id; 
     } 

     set 
     { 
      if (_id == value) 
      { 
       return; 
      } 

      RaisePropertyChanging(IdPropertyName); 
      _id = value; 
      RaisePropertyChanged(IdPropertyName); 
     } 
    } 

} 

XAML：

​​

所以，populateButton正在爲組合框綁定列表，SET按鈕設置ID爲3.然後，如果我填充列表再次choosen組合框中的ID是1.是不是應該還是3？我的意思是，不應該組合框爲ID = 3的模型設置Selected Item。

我也試過沒有IsSynchronizedWithCurrentItem設置爲true。然後重新加載列表後，組合框中沒有任何選擇。有沒有辦法使用ID同步selectedItem？

好像列表應該先初始化，然後我應該設置ID，所以組合框可以更新選定的項目。但是，那麼爲什麼如果我先使用setButton，然後填充，我會得到預期的結果（選擇的項目是第三項）（僅限第一次使用）？

Answer 1

您需要做的就是在重新填充列表後通知視圖：Id屬性已更改。

PopulateCommand = new RelayCommand(
    () => 
     { 
      Populate(); 
      RaisePropertyChanged(() => Id); 
     }); 

您不需要使用IsSynchronizedWithCurrentItem=true。這將用於（例如）保持兩個列表框同步並顯示相同的選定項目。