从列表视图更改为数据网格后的验证错误

我有一个验证良好的列表视图，但我想更改列表视图内部文本框的外观，所以我将其更改为 datagrid。我更改它后，验证被搞砸了。每当添加自动名称时，我都会收到错误消息，说该名称已经存在，即使它不存在。为什么列表视图没问题？欢迎任何意见。这是代码;

验证良好的列表视图：

   <ListView Name="_regionQueryListBox" Width="122" 
         HorizontalAlignment="Left" VerticalAlignment="Stretch" 
         DataContext="{Binding}"    IsSynchronizedWithCurrentItem="True"
         Style="{StaticResource ListViewRegionSelectorStyle}"
         ItemsSource="{Binding Path=Model}">
      <ListView.View>
          <GridView>
                <GridViewColumn Header="Region"
                   Width="{Binding Path=ActualWidth, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ListView}}">
                    <GridViewColumn.CellTemplate>
                        <DataTemplate>
                         <TextBox HorizontalAlignment="Left" VerticalAlignment="Stretch" 
                             Text="{Binding Path=RegionName}">
                                            </TextBox>
                                        </DataTemplate>
                                    </GridViewColumn.CellTemplate>
                                </GridViewColumn>
                            </GridView>
                        </ListView.View>
                    </ListView>

数据网格，验证不起作用：

<DataGrid x:Name="_regionQueryListBox" HorizontalAlignment="Left" VerticalAlignment="Stretch"
                          AutoGenerateColumns="False"
                          AlternatingRowBackground="Silver" AlternationCount="2"
                          CanUserReorderColumns="False" CanUserResizeColumns="False" CanUserSortColumns="False"
                          CanUserAddRows="False" CanUserDeleteRows="False" CanUserResizeRows="False" 
                          VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Disabled"
                          SelectionMode="Single"  
                          DataContext="{Binding}"
                          ItemsSource="{Binding Path=Model}" >
                        <DataGrid.Columns>
                            <DataGridTemplateColumn Header="Region" Width="110" >
                                <DataGridTemplateColumn.CellTemplate>
                                    <DataTemplate>
                                        <TextBox Text="{Binding Path=RegionName}" 
                                                 TextChanged="regionTextBox_TextChanged" >
                                        </TextBox>
                                    </DataTemplate>
                                </DataGridTemplateColumn.CellTemplate>
                            </DataGridTemplateColumn>
                        </DataGrid.Columns>
                    </DataGrid>

验证：

 private void regionTextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        {
            TextBox textBox = sender as TextBox;
            if (textBox != null)
            {
                string name = textBox.Text;
                StringBuilder errorMessage = null;
                RegionQueryViewModel queryViewModel = DataContext as RegionQueryViewModel;
                if (queryViewModel.Model.Any(q => q.RegionName == name))
                {
                    errorMessage = new StringBuilder();
                    errorMessage.AppendLine(string.Format("{0} already exists in the list.", name));
                }
                if (errorMessage != null)
                {
                    MessageBox.Show(errorMessage.ToString(), "Item Already Exists");
                    name = string.Empty;
                    //RegionName = name;
                    return;
                }
            }
        }

    <DataTemplate>
          <TextBox Text="{Binding Path=RegionName, UpdateSourceTrigger=PropertyChanged}" 
                   TextChanged="regionTextBox_TextChanged" />
    </DataTemplate>