wpf - Mvvm:如何从另一个 ViewModel 更新我的 ObservableCollection<customobject>？

Question

我很难理解如何在 ViewModel1 中定义的 ViewModel2 中更新 ObservableCollection。我已经搜索了很多关于如何做到这一点，但无法得到正确的理解。我正在使用 MVVM Light 框架。

我有一个 DozentViewModel，它有一个 ObservableCollection 的 Dozents。
我有另一个 AddDozentViewModel 用于通过 Entity Framework 将新的 Dozent 添加到数据库中。但是如何将新的 Dozent 添加到 DozentViewModel 中的 ObservableCollection 中？

这是我的 DozentViewModel:

public class DozentViewModel : ViewModelBase
{
    private IDozentDB _dozentDB;
    private ObservableCollection<Dozent> _dozentList;
    private string _nachName;
    private string _vorName;
    private string _akadGrad;

    public RelayCommand ShowAddDozentCommand { get; private set; }

    public ObservableCollection<Dozent> DozentList
    {
        get { return _dozentList; }
        set
        {
            Set(ref _dozentList, value);
            RaisePropertyChanged("DozentList");
        }

    }

    public DozentViewModel(IDozentDB dozentDB)
    {

        _dozentDB = dozentDB;
        DozentList = new ObservableCollection<Dozent>();

        // To get list of all Dozents  
        DozentList = _dozentDB.GetAllDozents();

        ShowAddDozentCommand = new RelayCommand(ShowAddDozentViewExecute);

    }

我已将 DozentList 属性绑定(bind)到我的 DozentView :
<DataGrid ItemsSource="{Binding DozentList,UpdateSourceTrigger=PropertyChanged}" AutoGenerateColumns="False" CanUserAddRows="False" IsReadOnly="True" Grid.Column="0" >
这是我的 AddDozentViewModel，它将新的 Dozent 添加到我的 SQL 数据库中。

public AddDozentViewModel(IDozentDB dozentDB)
    {
        _dozentDB = dozentDB;

        // To Add Dozent details to Dozent DB 
        AddCommand = new RelayCommand(AddDozent, CanAddDozent);

     }
    public string NachName
    {
        get { return _nachName; }
        set
        {
            Set(ref _nachName, value);
            RaisePropertyChanged("NachName");
            AddCommand.RaiseCanExecuteChanged();
        }
    }

    public string VorName
    {
        get { return _vorName; }
        set
        {
            Set(ref _vorName, value);
            RaisePropertyChanged("VorName");
            AddCommand.RaiseCanExecuteChanged();
        }
    }

    public string AkadGrad
    {
        get { return _akadGrad; }
        set
        {
            Set(ref _akadGrad, value);
            RaisePropertyChanged("AkadGrad");
            AddCommand.RaiseCanExecuteChanged();

        }
    }
    private void AddDozent()
    {
        Dozent dozent = new Dozent();
        dozent.DozentNachname = this.NachName;
        dozent.DozentVorname = this.VorName;
        dozent.AkadGrad = this.AkadGrad;

        _dozentDB.Create(dozent);



        Messenger.Default.Send(new NotificationMessage("CloseAddDozentView"));
    }

    private bool CanAddDozent()
    {
        return (!string.IsNullOrEmpty(NachName)) && (!string.IsNullOrEmpty(VorName)) && (!string.IsNullOrEmpty(AkadGrad));
    }

}

我知道我只是将新的 Dozent 添加到数据库中，而不是更新 ObservableCollection。因此我在 DozentView 上的 DataGridView 没有得到更新。我该怎么做呢？任何信息都会非常有帮助!!

谢谢，
维尼塔

Answer 1

我希望在这里做的事情类似于制作 AddDozentViewModel DozentViewModel 的属性(property)，其中将包含对其父级的引用，例如:

public class AddDozentViewModel
{
    private readonly DozentViewModel _parent;

    ...

    public AddDozentViewModel(DozentViewModel parent, IDozentDB dozentDB)
    {
        _parent = parent;
        _dozentDB = dozentDB;
    }

    ...

    private void AddDozent()
    {
        Dozent dozent = new Dozent();
        dozent.DozentNachname = this.NachName;
        dozent.DozentVorname = this.VorName;
        dozent.AkadGrad = this.AkadGrad;

        _dozentDB.Create(dozent);

        _parent.DozentList.Add(dozent);

        Messenger.Default.Send(new NotificationMessage("CloseAddDozentView"));

        _parent.AddDozentViewModel = null; // this will dispose of the AddDozentViewModel
    }

    ...
}

DozentViewModel因此看起来像这样:

public class DozentViewModel : ViewModelBase
{
    ...

    private AddDozentViewModel _addDozentViewModel;
    public AddDozentViewModel AddDozentViewModel
    {
        get { return _addDozentViewModel; }
        set
        {
            Set(ref _addDozentViewModel, value);
            RaisePropertyChanged("_addDozentViewModel");
        }
    }

    ...
}

另外，为了更加确定新的Dozent已写入数据库，所以我总是觉得我与数据库同步，我可能会考虑检索新的 Dozent从数据库中添加到 DozentList .所以这会改变 AddDozent()方法类似于:

private void AddDozent()
{
    Dozent dozent = new Dozent();
    dozent.DozentNachname = this.NachName;
    dozent.DozentVorname = this.VorName;
    dozent.AkadGrad = this.AkadGrad;

    _dozentDB.Create(dozent);

    Dozent newDozentFromDB = // retrieve it from _dozentDB here

    _parent.DozentList.Add(newDozentFromDB);

    Messenger.Default.Send(new NotificationMessage("CloseAddDozentView"));

    _parent.AddDozentViewModel = null; // this will dispose of the AddDozentViewModel
}