WPF SelectedItem无法在MVVM中运行

Question

我正在尝试显示两个与外键链接的sql ce 3.5 sp1数据库表中的数据 - 客户和订单.在datadrig中选择客户后,我希望使用订单填充其他网格.我正在使用查询:

var profiles = from c in db.Customers.Include("Orders")
                           select c;

在我的ViewModel中:

private Models.Customers _selecteditem;
        public Models.Customers SelectedItem
        {
            get { return _selecteditem; }

        }

视图看起来像这样:

<Grid>
        <toolkit:DataGrid  x:Name="dg1" ItemsSource="{Binding Customers}" SelectedItem="{Binding SelectedItem, mode=TwoWay}">
            </toolkit:DataGrid>
        <toolkit:DataGrid  x:Name="dg2" ItemsSource="{Binding Path=SelectedItem.Orders}">
        </toolkit:DataGrid>
    </Grid>

我得到的错误是:

Warning 1   Field 'Clients.ViewModels.CustomerViewModel._selecteditem' is never assigned to, and will always have its default value null    

如何让它正常工作？当我只是想显示客户时,这没关系.谢谢你的任何建议.

Answer 1

你需要一个SelectedItem的setter

private Models.Customers _selecteditem;
public Models.Customers SelectedItem
{
    get { return _selecteditem; }
    set { _selectedItem = value; }
}

此外,由于您在绑定中使用它,您将希望ViewModel实现INotifyPropertyChanged,因此它实际上是:

private Models.Customers _selecteditem;
public Models.Customers SelectedItem
{
    get { return _selecteditem; }
    set
    { 
      if (_selectedItem != value)
      {
        _selectedItem = value;
        NotifyPropertyChanged("SelectedItem");
      }
    }
}

public event PropertyChangedEventHandler PropertyChanged;

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