TwoWindowsModified

BaseWindowViewModel.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TwoWindows
{
    public class BaseWindowViewModel
    {
        public string PageTitle { get; set; }

        public ObservableCollection<MyCustomItemViewModel> MyItems { get; } = new ObservableCollection<MyCustomItemViewModel>();

    }
}

MainWindow.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace TwoWindows
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void ClickMe_Click(object sender, RoutedEventArgs e)
        {
            var windowBViewModel = new WindowBViewModel("WindowB");
            var windowB = new WindowB();

            var windowAViewModel = new WindowAViewModel("WindowA", windowBViewModel);
            var windowA = new WindowA();

            windowA.DataContext = windowAViewModel;
            windowA.Show();

            windowB.DataContext = windowBViewModel;
        }
    }
}

MainWindow.xaml

<Window x:Class="TwoWindows.MainWindow"
        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:WB="clr-namespace:TwoWindows"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
        
   
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="50"/>
        </Grid.RowDefinitions>
        <Button Grid.Row="1" Content="Click Me" Width="80" Height="25"  Click="ClickMe_Click"/>
        <TabControl Grid.Row="0" Margin="10">
            <TabItem>
                <TabItem.Header>
                    <StackPanel>
                        <TextBlock Text="WindowB"/>
                    </StackPanel>
                </TabItem.Header>
                <WB:WindowB/>
            </TabItem>
        </TabControl>
    </Grid>
</Window>

MyCustomItemViewModel.cs

using PropertyChanged;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TwoWindows
{
    [ImplementPropertyChanged]
    public class MyCustomItemViewModel
    {
        public string ItemName { get; set; }
        public bool IsChecked { get; set; }
        public WindowBViewModel WindowBViewModelObj { get; set; }

        public MyCustomItemViewModel(string itemName, WindowBViewModel windowBViewModel)
        {
            ItemName = itemName;
            WindowBViewModelObj = windowBViewModel;
        }

        private void OnIsCheckedChanged()
        {
            if (IsChecked)
                WindowBViewModelObj.MyItems.Add(this);
            else
                WindowBViewModelObj.MyItems.Remove(this);
        }
    }
}

WindowA.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace TwoWindows
{
    /// <summary>
    /// Interaction logic for WindowA.xaml
    /// </summary>
    public partial class WindowA : Window
    {
        public WindowA()
        {
            InitializeComponent();
        }
    }
}

WindowA.xaml

<Window x:Class="TwoWindows.WindowA"
        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:TwoWindows"
        mc:Ignorable="d"
        Title="WindowA" Height="300" Width="600">
         <Window.Resources>        
                 <CollectionViewSource x:Key='src' Source="{Binding BaseWindowViewModel}">            
                         <CollectionViewSource.SortDescriptions>                
                                 <scm:SortDescription PropertyName="ItemName"/>            
                         </CollectionViewSource.SortDescriptions>        
                 </CollectionViewSource>    
        </Window.Resources>
    <Grid>
        <Label Content="{Binding PageTitle}" />
        <ListBox ItemsSource="{Binding MyItems}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <CheckBox Content="{Binding ItemName}" IsChecked="{Binding IsChecked}"/>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

WindowAViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TwoWindows
{
    public class WindowAViewModel : BaseWindowViewModel
    {
        //WindowBViewModel windowBViewModel is to make WindowAViewModel sees WindowBViewModel
        public WindowAViewModel(string pageTitle, WindowBViewModel windowBViewModel)
        {
            PageTitle = pageTitle;

            MyItems.Add(new MyCustomItemViewModel("Apple", windowBViewModel));
            MyItems.Add(new MyCustomItemViewModel("Orange", windowBViewModel));
            MyItems.Add(new MyCustomItemViewModel("Banana", windowBViewModel));
        }
    }
}

WindowB.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

namespace TwoWindows
{
    /// <summary>
    /// Interaction logic for WindowB.xaml
    /// </summary>
    public partial class WindowB : UserControl
    {
        public WindowB()
        {
            InitializeComponent();
        }

        public WindowBViewModel DataContext { get; internal set; }
    }
}

WindowB.xaml

<UserControl x:Class="TwoWindows.WindowB"
        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:TwoWindows"
        mc:Ignorable="d">
    <Grid>
        <Label Content="{Binding PageTitle}" />
        <ListBox ItemsSource="{Binding MyItems}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Label Content="WindowB UserControl"/>
                        <TextBlock Text="{Binding ItemName}" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</UserControl>

WindowBViewModel.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TwoWindows
{
    public class WindowBViewModel : BaseWindowViewModel
    {
        public WindowBViewModel(string pageTitle)
        {
            PageTitle = pageTitle;
        }
    }
}