ObservableCollection 事件上的 ItemEndEdit 触发两次的问题

Question

我在数据网格插入/更新行两次时遇到问题。数据网格绑定到一个可观察集合，该集合添加了一个 ItemEndEdit 事件：

/// <summary>
/// extends the ObservableCollection class to include adding an ItemEndEdit event
/// </summary>
public class ObservableProjectExpenseItems : ObservableCollection<ProjectExpenseItemsBO>
{
    protected override void InsertItem(int index, ProjectExpenseItemsBO item)
    {
        base.InsertItem(index, item);
        item.ItemEndEdit += new ProjectExpenseItemsBO.ItemEndEditEventHandler((x) =>
        {
            if (ItemEndEdit != null)
                ItemEndEdit(x);
        });
    }

    public event ProjectExpenseItemsBO.ItemEndEditEventHandler ItemEndEdit;
}

ProjectExpenseItemsBO 是我的模型/业务对象，其中包含绑定在 dg 列中的属性。

当用户离开数据网格的行时，我在视图模型中使用以下内容来插入/更新记录：

    void ProjectExpenseItemsItemEndEdit(IEditableObject sender)
    {
        ProjectExpenseItemsBO projectExpenseItemsBO = sender as ProjectExpenseItemsBO;
        if (projectExpenseItemsBO.RowID == 0)
        {
            // if the ProjectExpenseItemsBO is a new row
            projectExpenseItemsRepository.AddProjectExpenseItem(projectExpenseItemsBO, this.ProjectExpenseID);
        }
        else
        {
            projectExpenseItemsRepository.UpdateProjectExpenseItem(projectExpenseItemsBO);
        }
        // get the total of the project expense items
        ItemTotal = projectExpenseItemsRepository.GetItemTotal(this.ProjectExpenseID);
    }

更新和插入都会触发两次，我不明白为什么。我在类/视图模型的初始化中附加了 ItemEndEdit：

ObservableProjectExpenseItems projectExpenseItemsCollection;
List<ProjectExpenseItemsBO> list = new List<ProjectExpenseItemsBO>(projectExpenseItemsRepository.GetProjectExpenseItems(this.ProjectExpenseID));
list.ForEach(item => ProjectExpenseItemsCollection.Add(item));
ProjectExpenseItemsCollection.ItemEndEdit += new ProjectExpenseItemsBO.ItemEndEditEventHandler(ProjectExpenseItemsItemEndEdit);

最后，这是我的数据网格：

<DataGrid ItemsSource="{Binding Path=ProjectExpenseItemsCollection}" Grid.Row="0" Grid.Column="0" AutoGenerateColumns="False" 
  Name="dgProjectExpenseItems" SelectionMode="Single" SelectionUnit="FullRow" CanUserResizeColumns="True" 
  SelectedItem="{Binding Path=SelectedProjectExpenseItem, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
  GridLinesVisibility="Horizontal" CanUserDeleteRows="True" CanUserAddRows="True">
  <DataGrid.RowValidationRules>
   <vr:RowDataInfoValidationRule ValidationStep="UpdatedValue" />
  </DataGrid.RowValidationRules>
  <DataGrid.Columns>
   <DataGridTextColumn Header="ID" Width="SizeToCells" IsReadOnly="True" MinWidth="50" Binding="{Binding RowID}" />
   <DataGridTextColumn Header="Project Expense ID" IsReadOnly="True" Width="SizeToCells" Visibility="Hidden" MinWidth="0" Binding="{Binding ProjectExpenseID, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
   <DataGridTextColumn Header="Item Number" Width="SizeToCells" MinWidth="140" Binding="{Binding ItemNumber, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
   <DataGridTextColumn Header="Item Description" Width="SizeToCells" MinWidth="250" Binding="{Binding ItemDescription, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
   <!--<DataGridTextColumn Header="Qty" Width="SizeToCells" MinWidth="65" Binding="{Binding ItemQty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />-->
   <DataGridTextColumn Header="Qty">
    <DataGridTextColumn.Binding>
     <Binding Path="ItemQty" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
      <Binding.ValidationRules>
       <vr:PositiveDecimalValidationRule ValidationStep="RawProposedValue" />
      </Binding.ValidationRules>
     </Binding>
    </DataGridTextColumn.Binding>
   </DataGridTextColumn>
   <DataGridTextColumn Header="Unit Price">
    <DataGridTextColumn.Binding>
     <Binding Path="ItemUnitPrice" Mode="TwoWay" UpdateSourceTrigger="PropertyChanged">
      <Binding.ValidationRules>
       <vr:PositiveDecimalValidationRule ValidationStep="RawProposedValue" />
      </Binding.ValidationRules>
     </Binding>
    </DataGridTextColumn.Binding>
   </DataGridTextColumn>
   <!--<DataGridTextColumn Header="Unit Price" Width="SizeToCells" MinWidth="90" Binding="{Binding ItemUnitPrice, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />-->
   <DataGridTextColumn Header="Supplier Name" Width="SizeToCells" MinWidth="200" Binding="{Binding SupplierName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
  </DataGrid.Columns>
 </DataGrid>

Answer 1

好吧。在尝试找出我遇到的另一个问题后，我偶然发现了导致事件触发两次的原因。当我在数据网格中保存一行时，我注意到保存前后主键字段值为零。显然，这是由于我在调用视图模型中的 save 方法后没有刷新集合。当我更改视图模型中的代码以刷新集合时：

    void ProjectExpenseItemsItemEndEdit(IEditableObject sender)
    {
        ProjectExpenseItemsBO projectExpenseItemsBO = sender as ProjectExpenseItemsBO;
        if (projectExpenseItemsBO.RowID == 0)
        {
            // use the data access layer to update the wrapped data object
            projectExpenseItemsRepository.AddProjectExpenseItem(projectExpenseItemsBO, this.ProjectExpenseID);
        }
        else
        {
            projectExpenseItemsRepository.UpdateProjectExpenseItem(projectExpenseItemsBO);
        }

        //refresh the collection
        ProjectExpenseItemsCollection.Clear();
        List<ProjectExpenseItemsBO> list = new List<ProjectExpenseItemsBO>(projectExpenseItemsRepository.GetProjectExpenseItems(this.ProjectExpenseID));
        list.ForEach(item => ProjectExpenseItemsCollection.Add(item));

        // get the total of the project expense items
        ItemTotal = projectExpenseItemsRepository.GetItemTotal(this.ProjectExpenseID);

    }

重复记录的问题消失了。哇，我已经为此工作了几个星期了。有趣的是，如此基本的东西会让你陷入困境这么长时间，尤其是当你试图学习新东西（wpf、mvvm）时。