Wpf CheckedListBox SelectedIndex in an ICommand

Question

I hope someone can help.
I am trying to follow MVVM principles and using .Net Core C#
I have a need to utilise a CheckedListBox so I am currently utilising the following simple solution:

<ListBox x:Name="PeopleListBox" Grid.Column="1" ItemsSource="{Binding PeopleCollection}" HorizontalContentAlignment="Stretch">  
                <ListBox.ItemTemplate>  
                <DataTemplate>  
                    <CheckBox x:Name="GridColumnVisibilityCheckBox" Content="{Binding FirstName}" HorizontalAlignment="Stretch" IsChecked="{Binding Path=IsSelected, Mode=TwoWay}"/>  
                </DataTemplate>  
                </ListBox.ItemTemplate>  
                </ListBox>  

I require a Command when ever an item IsSelected/Checked/Unchecked.
The command would need to have access to the SelectedIndex and whether the item was checked.
I appear to be going round in circles on this with no look and would very much appreciate some assistance, sample code for a solution.

Answer 1

Hi,
for resetting change your ViewModel:

using System;  
using System.Collections.ObjectModel;  
using System.ComponentModel;  
using System.Runtime.CompilerServices;  
using System.Threading;  
using System.Threading.Tasks;  
using System.Windows;  
using System.Windows.Data;  
using System.Windows.Input;  
  
namespace WpfApp035  
{  
 public class ViewModel : ICommand, INotifyPropertyChanged  
 {  
 private CollectionViewSource cvs = new();  
 public ICollectionView PeopleCollection  
 {  
 get  
 {  
 if (cvs.Source == null) cvs.Source = LoadData();  
 return cvs.View;  
 }  
 }  
  
 public People? LastItem { get; set; }  
  
 public event EventHandler? CanExecuteChanged;  
 public event PropertyChangedEventHandler? PropertyChanged;  
  
#pragma warning disable CS1998, CS4014, CS8602  
 public bool CanExecute(object? parameter) => true;  
 public async void Execute(object? parameter)  
 {  
 var item = (parameter == null) ? null : (People)parameter;  
 LastItem = item;  
 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(LastItem)));  
 Task.Factory.StartNew(() => ResetIsSelected(item));  
 }  
  
 private async void ResetIsSelected(People? p)  
 {  
 if (p == null) return;  
 await Task.Delay(1000);  
 p.IsSelected = false;  
 p.OnPropertyChanged("IsSelected");  
 }  
  
 private ObservableCollection<People> LoadData()  
 {  
 ObservableCollection<People> col = new();  
 for (int i = 1; i < 10; i++) col.Add(new People() { FirstName = $"FirstName {i}" });  
 return col;  
 }  
  
 public class People : INotifyPropertyChanged  
 {  
 public string FirstName { get; set; }  
 public bool IsSelected { get; set; }  
  
 public event PropertyChangedEventHandler? PropertyChanged;  
 internal void OnPropertyChanged([CallerMemberName] string propName = "") =>  
 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));  
 }  
 }  
}  

Result:

Answer 2

Hi,
to solve your problem you must bind Command of CheckBox to ICommand property in ViewModel and CommandParameter to actual item. See my demo:

<Window x:Class="WpfApp1.Window035"  
        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:WpfApp035"  
        mc:Ignorable="d"  
        Title="BigH61-8942_221215" Height="450" Width="800">  
  <Window.Resources>  
    <local:ViewModel x:Key="vm"/>  
  </Window.Resources>  
  <Grid DataContext="{StaticResource vm}">  
    <Grid.ColumnDefinitions>  
      <ColumnDefinition Width="100"/>  
      <ColumnDefinition/>  
    </Grid.ColumnDefinitions>  
    <Grid.RowDefinitions>  
      <RowDefinition/>  
      <RowDefinition/>  
    </Grid.RowDefinitions>  
    <ListBox Grid.Column="1" ItemsSource="{Binding PeopleCollection}" HorizontalContentAlignment="Stretch">  
      <ListBox.ItemTemplate>  
        <DataTemplate>  
          <CheckBox Content="{Binding FirstName}" HorizontalAlignment="Stretch"   
                    IsChecked="{Binding Path=IsSelected, Mode=TwoWay}"   
                    Command="{Binding Source={StaticResource vm}}" CommandParameter="{Binding}"/>  
        </DataTemplate>  
      </ListBox.ItemTemplate>  
    </ListBox>  
    <StackPanel Grid.Column="1" Grid.Row="1" DataContext="{Binding LastItem}">  
      <Label Content="Last checked / unchecked item"/>  
      <Label Content="  FirstName"/>  
      <TextBlock Text="{Binding FirstName}"/>  
      <Label Content="  IsSelected"/>  
      <TextBlock Text="{Binding IsSelected}"/>  
    </StackPanel>  
  </Grid>  
</Window>  

and ViewModel:

Result: