datagrid and observablecollection propblem

Question

hi,
i have a datagrid in my view bound to observablecollection<myClass>, the propblem occurs when i set datagrid.CanUserAddRows to "True" , it adds a null object to the end of my observablecollection,
and this observablecollection bound to another itemscontrol control as ItemsSource in another view.

Q1: how to prevent my datagrid from adding null object to my collection ?
Q2: how to prevent my itemscontrol from seeing the null element (the one that created automatically by datagrid) ?

thanks in advance.
i'm using VS2019 last version , wpr.core app.

Answer 1

For my purpose I don't use DataGrid at all for anything. For reporting ItemsControl, ListBox, etc. are more than enough. For adding objects into collection I create small input form with validation and when is valid I let it to get added into collection.

To hide the null in your ItemsControl, create a DataTrigger and check for x:Null. If it is null (last item) which in fact always will be, keep it collapsed.

Answer 2

Hi,
if you use a second View with the same Source you don't see null elements. Try following demo with

XAML

<Window x:Class="WpfApp1.Window07"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:WpfApp07"  
        mc:Ignorable="d"  
        Title="Window07" Height="450" Width="800">  
  <Window.DataContext>  
    <local:ViewModel/>  
  </Window.DataContext>  
  <Grid>  
    <Grid.ColumnDefinitions>  
      <ColumnDefinition/>  
      <ColumnDefinition/>  
    </Grid.ColumnDefinitions>  
    <DataGrid ItemsSource="{Binding View1}"/>  
    <ListBox Grid.Column="1" ItemsSource="{Binding View2}">  
      <ListBox.ItemTemplate>  
        <DataTemplate>  
          <Label Content="{Binding Info}"/>  
        </DataTemplate>  
      </ListBox.ItemTemplate>  
    </ListBox>  
  </Grid>  
</Window>  

And classes:

using System.Collections.ObjectModel;  
using System.ComponentModel;  
using System.Windows;  
using System.Windows.Data;  
  
namespace WpfApp07  
{  
  public class ViewModel  
  {  
    ObservableCollection<Data> col = new ObservableCollection<Data>();  
    CollectionViewSource cvs = new CollectionViewSource();  
    public ViewModel() => cvs.Source = col;  
    public ICollectionView View1 { get => cvs.View; }  
    public ICollectionView View2 { get => cvs.View; }  
  }  
  
  public class Data  
  {  
    public int ID { get; set; }  
    public string Info { get; set; }  
  }  
}  

Result: