更新ObservableCollection之后，没有使用Datagrid Edit的新行

Question

I have been having an issue with a DataGrid not making a new empty row after a new record has been entered.

It seems to only occur after updating the ObversableCollection<T> .

I use this to bind to the collection:

public partial class MainWindow : INotifyPropertyChanged
{
    public MainWindow()
    {
    DataContext = this; 
    InitializeComponent();       

    CollectionLists.CalculationTableSourceCollection(CalculationTblSourceObserv, @"section", @"sectionAll");
    CalculationTableGrid.ItemsSource = CalculationTblSourceObserv;
    }
public ObservableCollection<CalculationListTbl> CalculationTblSourceObserv { get; set; } 
 = new ObservableCollection<CalculationListTbl>();
}

This is my code for updating my ObversableCollection<T> :

class CollectionLists
{
public static void CalculationTableSourceCollection(ObservableCollection<CalculationListTbl> observable,
  string section, string sectionAll)
    {
            using (DatabaseDataContext dataContext = new DatabaseDataContext(MainWindow.InstanceConnectionString))
        {
            observable.Clear();
            var source = DatabaseQueries.CalculationTableSourceAll(sectionAll, dataContext);
            if (source == null) return;
            foreach (var item in source)
            {
                observable.Add(item);
            }
        }
    }
}

And this is the XAML:

<DataGrid x:Name="CalculationTableGrid" Grid.Column="2" 
       AutoGenerateColumns="False" ItemsSource="{Binding}" 
       Grid.Row="1" Grid.RowSpan="12" AlternationCount="2" 
       CanUserAddRows="True" CanUserSortColumns="False" 
       CanUserDeleteRows="True" GridLinesVisibility="None" 
       CellEditEnding="CalculationTableGrid_OnCellEditEnding" 
       VerticalAlignment="Top">

    <DataGrid.Columns>
        <DataGridTextColumn Width="*" Header="項目" 
           Binding="{Binding UpdateSourceTrigger=PropertyChanged, Path=ListItems, Mode=TwoWay}" />
    </DataGrid.Columns>

</DataGrid>

And I use this method to update the dataGrid :

private void CalculationTableGrid_OnCellEditEnding(object sender, DataGridCellEditEndingEventArgs e)
{
     ShiftTypeData.UserInputData.AddNewDataShiftInputRecords(e, MainUserId, EmployeesNameNumberPairsAll, CalculationTblListObserv, DateFilter);
     CollectionLists.CalculationTableSourceCollection(CalculationTblSourceObserv, @"section", @"sectionAll");               
}

So everything works fine, the DataGrid' is updated, the database is correctly updated and the ObversableCollection is updated. However the is updated. However the DataGrid` should be added a new row after the new record is inserted, but this is what it does.

This is what it does,

However, commenting out this line CollectionLists.CalculationTableSourceCollection(CalculationTblSourceObserv, @"section", @"sectionAll"); in the CalculationTableGrid_OnCellEditEnding event allows it to correctly behave and an empty row is added after the new record is made, see below:

What is going on here, I can't get this to work correctly, any help would be much appreciated.

Answer 1

It seems like you are updating property CalculationTblSourceObserv but you have bounded the property ListItems in the xaml. so either bind CalculationTblSourceObserv in xaml or you can do following.

In your question I can't see which part of code does the property 'ListItems' is present, which is the property binded to the datagrid. Hopefully this is in a view model.

So either your property 'ListItems' is not getting updated or if it is getting updated then your xaml is not notified about that change. Your view model code should notify the xaml that a property has been updated. This is done via Raising a property changed event which can be done like this:

public string ListItems
{
    get { return listItems; }
    set
    {
         listItems= value;
         // Call OnPropertyChanged whenever the property is updated
         OnPropertyChanged("ListItems");
     }
}

  // Create the OnPropertyChanged method to raise the event
  protected void OnPropertyChanged(string name)
  {
      PropertyChangedEventHandler handler = PropertyChanged;
      if (handler != null)
      {
          handler(this, new PropertyChangedEventArgs(name));
      }
  }

Further refer to link: How to: Implement Property Change Notification

Answer 2

The issue here is that the CellEditEnding event will be raised when the new item is added and then you immediately clear your CalculationTableSourceCollection in your CalculationTableSourceCollection method.

You don't have to call the CalculationTableSourceCollection method in the CellEditEnding event handler at all.

Any item that you add or remove to an ObservableCollection<T> will automatically show up in the DataGrid . This is what makes an ObservableCollection<T> different from a List<T> . The latter doesn't implement the INotifyCollectionChanged interface.