I can't count the selected DataGrid rows correctly to delete them, DataGrid.SelectedItems.Count doesn't give me the exact number of them. In WPF (by C#)

Question

I can't count the selected DataGrid rows correctly to delete them, DataGrid.SelectedItems.Count doesn't give me the exact number of them. In WPF (by C#)

رضا جافری 1,296

First and foremost, I apologize for my grammatical errors; my first language is Persian (Iran).
I want to remove one or more rows from DataGrid depending on the user's choice.
I add blank rows to the DataGrid with the following codes:

    public struct DefaultRow  
    {  
        public string NO { get; set; }  
        public string ID_Serial { get; set; }  
        public string ProductsOrServicesDescription { get; set; }  
        public string Quantity { get; set; }  
        public string UnitOfMeasurement { get; set; }  
        public string UnitPrice { get; set; }  
        public string Discount { get; set; }  
        public string TaxDutyVat { get; set; }  
        public string GuaranteeOrWarrantyPeriod { get; set; }  
        public string TotalAmount { get; set; }  
    }  
    public void AddBlankRow()  
    {  
        List<object> DefaultRow = new List<object>();  
        DefaultRow DR = new DefaultRow();  
        DR.NO = "";  
        DR.ID_Serial = "";  
        DR.ProductsOrServicesDescription = "";  
        DR.Quantity = "";  
        DR.UnitOfMeasurement = "";  
        DR.UnitPrice = "";  
        DR.Discount = "";  
        DR.TaxDutyVat = "";  
        DR.GuaranteeOrWarrantyPeriod = "";  
        DR.TotalAmount = "";  
        for (int i = 0; i < BillDataGrid.Items.Count; i++)  
        {  
            DefaultRow.Add(BillDataGrid.Items[i]);  
        }  
        DefaultRow.Add(DR);  
        BillDataGrid.ItemsSource = DefaultRow;  
    }  
    private void AddNewRow_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)  
    {  
        AddBlankRow();  
    }

When I try to fill the blank rows, DataGrid.SelectedItems.Count increases with each click, then when I want to select a number of rows again to delete, I get the following error:
System.ArgumentOutOfRangeException: 'Index was out of range. Must be non-negative and less than the size of the collection.'
These are my codes:
WPF:

                <DataGrid x:Name="BillDataGrid" HeadersVisibility="Column" CanUserAddRows="True" CanUserDeleteRows="True" EnableRowVirtualization="True" AutoGenerateColumns="False" HorizontalAlignment="Left" VerticalAlignment="Top" Height="190" Width="758" Margin="7,12,0,0">  
                    <DataGrid.Columns>  
                        <DataGridTextColumn x:Name="NO" Binding="{Binding NO}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="ID_Serial" Binding="{Binding ID_Serial}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="ProductsOrServicesDescription" Binding="{Binding ProductsOrServicesDescription}" Width="115"/>  
                        <DataGridTextColumn x:Name="Quantity" Binding="{Binding Quantity}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="UnitOfMeasurement" Binding="{Binding UnitOfMeasurement}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="UnitPrice" Binding="{Binding UnitPrice}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="Discount" Binding="{Binding Discount}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="TaxDutyVat" Binding="{Binding TaxDutyVat}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="GuaranteeOrWarrantyPeriod" Binding="{Binding GuaranteeOrWarrantyPeriod}" Width="SizeToHeader"/>  
                        <DataGridTextColumn x:Name="TotalAmount" Binding="{Binding TotalAmount}" Width="SizeToHeader"/>  
                    </DataGrid.Columns>  
                </DataGrid>

C#:

    private void DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)  
    {  
        switch (BillDataGrid.SelectedItems.Count > 0)  
        {  
            case false:  
                break;  
            default:  
                List<object> DefaultRow = new List<object>();  
                for (int i = 0; i < BillDataGrid.Items.Count; i++)  
                {  
                    DefaultRow.Add(BillDataGrid.Items[i]);  
                }  
                for (int i = 0; i < BillDataGrid.SelectedItems.Count; i++)  
                {  
                    DefaultRow.RemoveAt(BillDataGrid.SelectedItems.IndexOf(BillDataGrid.SelectedItems[i]));  
                }  
                BillDataGrid.ItemsSource = DefaultRow;  
                break;  
        }  
    }

Also, I tried to remove the selected rows from the DataGrid directly with the help of the following codes, but I got another error:

    private void DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)  
    {  
        switch (BillDataGrid.SelectedItems.Count > 0)  
        {  
            case false:  
                break;  
            default:;  
                for (int i = 0; i < BillDataGrid.SelectedItems.Count; i++)  
                {  
                    BillDataGrid.Items.Remove(BillDataGrid.SelectedItems[i]);  
                }  
                break;  
        }  
    }

System.InvalidOperationException: 'Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource instead.'

Thanks

رضا جافری 1,296 Reputation points

2022-01-15T13:18:35.167+00:00

Can anyone help me?

Answer accepted by question author

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Your answer

رضا جافری 1,296 Reputation points

2022-01-15T13:18:35.167+00:00

Can anyone help me?

Answer 1

Hi Reza,
you must iterate thru SelectedItems in descending order and remove form items collection (not from SelectedItems collection). I changed your demo. try it.

XAML:

<Window x:Class="WpfApp1.Window098"
        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:WpfApp098"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        mc:Ignorable="d"
        Title="RezaJafery_220115" Height="450" Width="900">
  <Window.DataContext>
    <local:ViewModel/>
  </Window.DataContext>
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition/>
      <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <DataGrid x:Name="BillDataGrid" 
              HeadersVisibility="Column" 
              CanUserAddRows="False" 
              CanUserDeleteRows="False" 
              EnableRowVirtualization="True" 
              AutoGenerateColumns="False" 
              HorizontalAlignment="Left" 
              VerticalAlignment="Top" 
              Margin="5">
      <i:Interaction.Behaviors>
        <local:DataGridBehavior/>
      </i:Interaction.Behaviors>
      <DataGrid.Columns>
        <DataGridTextColumn Header="NO" Binding="{Binding NO}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="ID_Serial" Binding="{Binding ID_Serial}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="ProductsOrServicesDescription" Binding="{Binding ProductsOrServicesDescription}" Width="115"/>
        <DataGridTextColumn Header="Quantity" Binding="{Binding Quantity}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="UnitOfMeasurement" Binding="{Binding UnitOfMeasurement}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="UnitPrice" Binding="{Binding UnitPrice}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="Discount" Binding="{Binding Discount}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="TaxDutyVat" Binding="{Binding TaxDutyVat}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="GuaranteeOrWarrantyPeriod" Binding="{Binding GuaranteeOrWarrantyPeriod}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="TotalAmount" Binding="{Binding TotalAmount}" Width="SizeToHeader"/>
      </DataGrid.Columns>
    </DataGrid>
    <StackPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right">
      <Button Content="Add New Row" Command="{Binding}" CommandParameter="AddNewRow" Width="100" Margin="5"/>
      <Button Content="Delete selected rows" Command="{Binding}" CommandParameter="DeleteSelectedRows" Width="100" Margin="5"/>
    </StackPanel>
  </Grid>
</Window>

and code:

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Interactivity;

namespace WpfApp098
{
  public class ViewModel : ICommand
  {
    public DataGrid BillDataGrid { get; set; }
    int NO;

    public void AddBlankRow()
    {
      List<object> DefaultRow = new List<object>();
      DefaultRow DR = new DefaultRow();
      DR.NO = (++NO).ToString(); //  "";
      DR.ID_Serial = "";
      DR.ProductsOrServicesDescription = "";
      DR.Quantity = "";
      DR.UnitOfMeasurement = "";
      DR.UnitPrice = "";
      DR.Discount = "";
      DR.TaxDutyVat = "";
      DR.GuaranteeOrWarrantyPeriod = "";
      DR.TotalAmount = "";
      for (int i = 0; i < BillDataGrid.Items.Count; i++)
      {
        DefaultRow.Add(BillDataGrid.Items[i]);
      }
      DefaultRow.Add(DR);
      BillDataGrid.ItemsSource = DefaultRow;
    }

    private void DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
      switch (BillDataGrid.SelectedItems.Count > 0)
      {
        case false:
          break;
        default:
          List<object> DefaultRow = new List<object>();
          for (int i = 0; i < BillDataGrid.Items.Count; i++)
          {
            DefaultRow.Add(BillDataGrid.Items[i]);
          }
          for (int i = BillDataGrid.SelectedItems.Count - 1; i >= 0; i--)
          {
            DefaultRow.RemoveAt(BillDataGrid.Items.IndexOf(BillDataGrid.SelectedItems[i]));
          }
          BillDataGrid.ItemsSource = DefaultRow;
          break;
      }
    }

    //private void DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    //{
    //  switch (BillDataGrid.SelectedItems.Count > 0)
    //  {
    //    case false:
    //      break;
    //    default:
    //      ;
    //      for (int i = 0; i < BillDataGrid.SelectedItems.Count; i++)
    //      {
    //        BillDataGrid.Items.Remove(BillDataGrid.SelectedItems[i]);
    //      }
    //      break;
    //  }
    //}

    public event EventHandler CanExecuteChanged;
    public bool CanExecute(object parameter) => true;
    public void Execute(object parameter)
    {
      switch (parameter.ToString())
      {
        case "AddNewRow": AddBlankRow(); break;
        case "DeleteSelectedRows": DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(null, null); break;
        default: break;
      }
    }
  }

  public class DefaultRow
  {
    public string NO { get; set; }
    public string ID_Serial { get; set; }
    public string ProductsOrServicesDescription { get; set; }
    public string Quantity { get; set; }
    public string UnitOfMeasurement { get; set; }
    public string UnitPrice { get; set; }
    public string Discount { get; set; }
    public string TaxDutyVat { get; set; }
    public string GuaranteeOrWarrantyPeriod { get; set; }
    public string TotalAmount { get; set; }
  }

  public class DataGridBehavior : Behavior<DataGrid>
  {
    protected override void OnAttached() =>
      AssociatedObject.Loaded += (s, e) =>
      ((ViewModel)AssociatedObject.DataContext).BillDataGrid = AssociatedObject;
  }
}

A better solution is to use collection and ItemsSource. Try following demo:

XAML:

<Window x:Class="WpfApp1.Window099"
        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:WpfApp099"
        xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
        mc:Ignorable="d"
        Title="RezaJafery_220115" Height="450" Width="900">
  <Window.DataContext>
    <local:ViewModel/>
  </Window.DataContext>
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition/>
      <RowDefinition Height="Auto"/>
    </Grid.RowDefinitions>
    <DataGrid ItemsSource="{Binding View}"
              HeadersVisibility="Column" 
              CanUserAddRows="False" 
              CanUserDeleteRows="False" 
              EnableRowVirtualization="True" 
              AutoGenerateColumns="False" 
              HorizontalAlignment="Left" 
              VerticalAlignment="Top" 
              Margin="5">
      <i:Interaction.Behaviors>
        <local:DataGridBehavior/>
      </i:Interaction.Behaviors>
      <DataGrid.Columns>
        <DataGridTextColumn Header="NO" Binding="{Binding NO}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="ID_Serial" Binding="{Binding ID_Serial}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="ProductsOrServicesDescription" Binding="{Binding ProductsOrServicesDescription}" Width="115"/>
        <DataGridTextColumn Header="Quantity" Binding="{Binding Quantity}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="UnitOfMeasurement" Binding="{Binding UnitOfMeasurement}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="UnitPrice" Binding="{Binding UnitPrice}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="Discount" Binding="{Binding Discount}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="TaxDutyVat" Binding="{Binding TaxDutyVat}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="GuaranteeOrWarrantyPeriod" Binding="{Binding GuaranteeOrWarrantyPeriod}" Width="SizeToHeader"/>
        <DataGridTextColumn Header="TotalAmount" Binding="{Binding TotalAmount}" Width="SizeToHeader"/>
      </DataGrid.Columns>
    </DataGrid>
    <StackPanel Grid.Row="1" Orientation="Horizontal" HorizontalAlignment="Right">
      <Button Content="Add New Row" Command="{Binding}" CommandParameter="AddNewRow" Width="100" Margin="5"/>
      <Button Content="Delete selected rows" Command="{Binding}" CommandParameter="DeleteSelectedRows" Width="100" Margin="5"/>
    </StackPanel>
  </Grid>
</Window>

And code:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Interactivity;

namespace WpfApp099
{
  public class ViewModel : ICommand
  {
    public DataGrid BillDataGrid { get; set; }
    int NO;

    public ViewModel() => cvs.Source = col;
    ObservableCollection<DefaultRow> col = new ObservableCollection<DefaultRow>();
    private CollectionViewSource cvs = new CollectionViewSource();
    public ICollectionView View { get => cvs.View; }

    public void AddBlankRow()
    {
      DefaultRow DR = new DefaultRow();
      DR.NO = (++NO).ToString(); //  "";
      DR.ID_Serial = "";
      DR.ProductsOrServicesDescription = "";
      DR.Quantity = "";
      DR.UnitOfMeasurement = "";
      DR.UnitPrice = "";
      DR.Discount = "";
      DR.TaxDutyVat = "";
      DR.GuaranteeOrWarrantyPeriod = "";
      DR.TotalAmount = "";
      col.Add(DR);
    }

    private void DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
      switch (BillDataGrid.SelectedItems.Count > 0)
      {
        case false:
          break;
        default:
          List<DefaultRow> cache = new List<DefaultRow>();
          foreach (var item in BillDataGrid.SelectedItems) cache.Add((DefaultRow)item);
          foreach (DefaultRow item in cache) col.Remove(item);
          break;
      }
    }

    public event EventHandler CanExecuteChanged;
    public bool CanExecute(object parameter) => true;
    public void Execute(object parameter)
    {
      switch (parameter.ToString())
      {
        case "AddNewRow": AddBlankRow(); break;
        case "DeleteSelectedRows": DeleteSelectedRows_Button_PreviewMouseLeftButtonDown(null, null); break;
        default: break;
      }
    }
  }

  public class DefaultRow
  {
    public string NO { get; set; }
    public string ID_Serial { get; set; }
    public string ProductsOrServicesDescription { get; set; }
    public string Quantity { get; set; }
    public string UnitOfMeasurement { get; set; }
    public string UnitPrice { get; set; }
    public string Discount { get; set; }
    public string TaxDutyVat { get; set; }
    public string GuaranteeOrWarrantyPeriod { get; set; }
    public string TotalAmount { get; set; }
  }

  public class DataGridBehavior : Behavior<DataGrid>
  {
    protected override void OnAttached() =>
      AssociatedObject.Loaded += (s, e) =>
      ((ViewModel)AssociatedObject.DataContext).BillDataGrid = AssociatedObject;
  }
}

رضا جافری 1,296 Reputation points

2022-01-15T21:24:08.967+00:00

Hi, PeterFleischer-3316
I correct my text.
Your code need one reference, which exists in my system.

If you really tested this code, can you tell me how to use it?
رضا جافری 1,296 Reputation points

2022-01-15T21:27:34.11+00:00

Does anyone know an easier solution?
Peter Fleischer (former MVP) 19,351 Reputation points

2022-01-15T21:57:11.703+00:00

Hi Reza,
I tested my posted code. It's a very easy solution. Behavior you must get from Nuget and delete Reference to XAML.Behavior or use alias. See result (my second code).
رضا جافری 1,296 Reputation points

2022-01-16T23:16:19.433+00:00

Hi, PeterFleischer-3316
I'm sorry to ask you so many questions.
I solved the refrences problem, but I don't know how to use your code, can you explain how to use your second code in AddNewRow_Button_PreviewMouseLeftButtonDown and DeleteSelectedRows_Button_PreviewMouseLeftButtonDown events?
I used your code again as shown below but this time it does not work by clicking.

Thanks
Peter Fleischer (former MVP) 19,351 Reputation points

2022-01-17T05:25:41.637+00:00

Hi Reza,
copy my code without changes in a new project und test it. It works without problems.
رضا جافری 1,296 Reputation points

2022-01-17T23:06:26.907+00:00

Hi, PeterFleischer-3316
I complete your answer, so that others can use it.
I forgot the following code:
Command = "{Binding}" CommandParameter = "AddNewRow" and Command = "{Binding}" CommandParameter = "DeleteSelectedRows"
And I mistakenly used the PreviewMouseLeftButtonDown event instead.

Note: If you added the references correctly, you also entered the C # and XAML codes correctly, and you got an error from the following two codes before compiling, do not worry, run the program, the errors will be fixed as shown below.

<Window.DataContext> <local:ViewModel/> </Window.DataContext> <i:Interaction.Behaviors> <local:DataGridBehavior/> </i:Interaction.Behaviors>

Output:

Thank you for your attention

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I can't count the selected DataGrid rows correctly to delete them, DataGrid.SelectedItems.Count doesn't give me the exact number of them. In WPF (by C#)

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