WPF

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private List<ProcessingOutputEntryEntity> _ProcesssingOutputEntries;
public List<ProcessingOutputEntryEntity> ProcesssingOutputEntries
{
    get { return _ProcesssingOutputEntries; }
    set
    {
        if (_ProcesssingOutputEntries != value)

        {
            _ProcesssingOutputEntries = value;
            RaisePropertyChanged(nameof(ProcesssingOutputEntries));
        }
    }
}

public class ProcessingOutputEntryEntity : _EntityBase
{
    private List<ColumnInfoEntity> _ProcesssingOutputColumns;
    public List<ColumnInfoEntity> ProcesssingOutputColumns
    {
        get { return _ProcesssingOutputColumns; }
        set
        {
            if (_ProcesssingOutputColumns != value)
            {
                _ProcesssingOutputColumns = value;
                RaisePropertyChanged(nameof(ProcesssingOutputColumns));
            }
        }
    }
}

public class ColumnInfoEntity : _EntityBase
{
    private string _ColumnName;
    public string ColumnName
    {
        get { return _ColumnName; }
        set
        {
            if (_ColumnName != value)
            {
                _ColumnName = value;
                RaisePropertyChanged(nameof(ColumnName));
            }
        }
    }

    private ColumnSources _ColumnSource;
    public ColumnSources ColumnSource
    {
        get { return _ColumnSource; }
        set
        {
            if (_ColumnSource != value)
            {
                _ColumnSource = value;
                RaisePropertyChanged(nameof(ColumnSource));
            }
        }
    }

    private ColumnTypes _ColumnType;
    public ColumnTypes ColumnType
    {
        get { return _ColumnType; }
        set
        {
            if (_ColumnType != value)
            {
                _ColumnType = value;
                RaisePropertyChanged(nameof(ColumnType));
            }
        }
    }

    private int _ColumnWidth;
    public int ColumnWidth
    {
        get { return _ColumnWidth; }
        set
        {
            if (_ColumnWidth != value)
            {
                _ColumnWidth = value;
                RaisePropertyChanged(nameof(ColumnWidth));
            }
        }
    }

    private string _DisplayAs;
    public string DisplayAs
    {
        get { return _DisplayAs; }
        set
        {
            if (_DisplayAs != value)
            {
                _DisplayAs = value;
                RaisePropertyChanged(nameof(DisplayAs));
            }
        }
    }

    private int _IndexPosition;
    public int IndexPosition
    {
        get { return _IndexPosition; }
        set
        {
            if (_IndexPosition != value)
            {
                _IndexPosition = value;
                RaisePropertyChanged(nameof(IndexPosition));
            }
        }
    }

    private bool _IsUserEditable = true;
    public bool IsUserEditable
    {
        get { return _IsUserEditable; }
        set
        {
            if (_IsUserEditable != value)
            {
                _IsUserEditable = value;
                RaisePropertyChanged(nameof(IsUserEditable));
            }
        }
    }

    private object _Data;
    public object Data
    {
        get { return _Data; }
        set
        {
            if (_Data != value)
            {
                _Data = value;
                RaisePropertyChanged(nameof(Data));
            }
        }
    }

    public override string ToString()
    {
        return $"{ColumnSource} {IndexPosition} {ColumnName}";
    }
}

private void WindowLoadedExecuted()
{
    // At this point, the row objects don't have an Id, so create one for each row.
    _results.ProcesssingOutputEntries.ForEach(x => x.Id = Guid.NewGuid());

    // Now, add an Id column in front of all other columns
    foreach (var entry in _results.ProcesssingOutputEntries)
    {
        var col = new ColumnInfoEntity
        {
            ColumnName = "Id",
            Data = entry.Id.ToString()
        };

        entry.ProcesssingOutputColumns.Insert(0, col);
    }

    DataColumn column = null;

    // Add data table columns using the column info objects on the first processing object
    var firstEntry = _results.ProcesssingOutputEntries.FirstOrDefault();
    foreach (var col in firstEntry.ProcesssingOutputColumns)
    {
        column = new DataColumn
        {
            DataType = Type.GetType("System.String"),
            ReadOnly = false
        };
        ColumnsDataTable.Columns.Add(column);
    }

    // Get the index positions of the AutoAdjustment and AutoPosting columns, so we can make all
    // other columns read-only
    var autoAdjColIndex = -1;
    var autoPostColIndex = -1;

    var autoAdjCol = GetProcessingOutputColumn(ColumnTypes.AutoAdjustment);

    if(autoAdjCol != null)
    {
        autoAdjColIndex = firstEntry.ProcesssingOutputColumns.IndexOf(autoAdjCol);
    }

    var autoPostCol = GetProcessingOutputColumn(ColumnTypes.AutoPosting);

    if (autoPostCol != null)
    {
        autoPostColIndex = firstEntry.ProcesssingOutputColumns.IndexOf(autoPostCol);
    }

    // Get a list of column names from the data table created above
    string[] columnNames = (from dc in ColumnsDataTable.Columns.Cast()
                            select dc.ColumnName).ToArray();

    // Create styles for the cells
    var textBoxStyle = new Style();
    textBoxStyle.Setters.Add(new Setter(TextBox.TextAlignmentProperty, TextAlignment.Right));

    var comboBoxStyle = new Style();
    comboBoxStyle.Setters.Add(new EventSetter(ComboBox.SelectionChangedEvent, new SelectionChangedEventHandler(ComboSelectionChanged)));

    // Go through each column
    int index = 0;
    foreach (string columnName in columnNames)
    {
        // Create binding
        var binding = new Binding(columnName);

        // If the column is the AutoAdjustment or AutoPosting column, add combo box columns
        // These two columns will be the right most two
        if (index == autoAdjColIndex || index == autoPostColIndex)
        {
            // Add a combo box column for it
            var col = new DataGridComboBoxColumn()
            {
                Header = firstEntry.ProcesssingOutputColumns[index].ColumnName,
                ItemsSource = new List { "Y", "N" },
                Visibility = Visibility.Visible,
                TextBinding = binding,
                IsReadOnly = false,
                CellStyle = comboBoxStyle,<br />
            };
            DataGridColumns.Add(col);
        }
        else
        {
            // Otherwise, add a read-only textbox column for it
            var col = new DataGridTextColumn()
            {
                Header = firstEntry.ProcesssingOutputColumns[index].ColumnName,
                Binding = binding,
                Visibility = Visibility.Visible,
                IsReadOnly = true,
                CellStyle = textBoxStyle
            };
            DataGridColumns.Add(col);
        }

        index++;
    }

    // Hide the first column, the Id
    //DataGridColumns.FirstOrDefault().Visibility = Visibility.Hidden;

    // Load the data into the grid
    LoadData();
}

private void LoadData()
{
    ColumnsDataTable.Clear();

    foreach (var processingEntry in _results.ProcesssingOutputEntries)
    {
        // Create a new row
        DataRow row = ColumnsDataTable.NewRow();
        ColumnsDataTable.Rows.Add(row);

        // Add each column's data
        var index = 0;
        foreach (var col in processingEntry.ProcesssingOutputColumns)
        {
            row[index] = col.Data;
            index++;
        }
    }
}

var comboBoxStyle = new Style();
comboBoxStyle.Setters.Add(new EventSetter(ComboBox.SelectionChangedEvent, new SelectionChangedEventHandler(ComboSelectionChanged)));

private void ComboSelectionChanged(object sender, SelectionChangedEventArgs e)
{
    // Find the selected row
    var comboBox = e.Source as ComboBox;
    var dataGrid = WPFTools.GetVisualParent(comboBox);
    var dataRowView = dataGrid.SelectedItem as DataRowView;

    if(dataRowView != null)
    {
        // Get the new selection from the combo box. It will be either 'Y' or 'N'
        var newSelection = e.AddedItems[0];

        // Get the row's Id
        var rowId = dataRowView.Row[0].ToString();
    }
}

public class ComboBoxWatermarkBehavior : Behavior<ComboBox>
.
.
.

public class TestControl : Label 
{
    public static readonly DependencyProperty dependencyPropertyTestInfo =
        DependencyProperty.Register("TestInfo", typeof(string), typeof(TestControl),
            new PropertyMetadata("", new PropertyChangedCallback(ChangeTestInfo)));

    public string TestInfo
    {
        get => (string)GetValue(dependencyPropertyTestInfo);
        set => SetValue(dependencyPropertyTestInfo, value);
    }
    private static void ChangeTestInfo(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var testControl = (TestControl)d;
        testControl.TestInfo = (string)e.NewValue;
    }
}

<StackPanel>
    <local:TestControl Content="TestControl" x:Name="tct" TestInfo="{Binding TestInfoView}"/>
    <Button Content="show TestInfo by Button-Click in xaml.cs" x:Name="BtnShow" Click="BtnShow_Click"/>
    <Button Content="set new TestInfo" Name="BtnNewTestInfo" Command="{Binding NewTestInfoCommand}"/>
</StackPanel>

public class MainWindowViewModel : BindableBase
{
    private int counter;
    private string _testInfoView;
    public string TestInfoView
    {
        get { return _testInfoView; }
        set { SetProperty(ref _testInfoView, value); }
    }
    public DelegateCommand NewTestInfoCommand { get; }
    public MainWindowViewModel()
    {
        NewTestInfoCommand = new DelegateCommand(OnNewTestInfoCommand);
        TestInfoView = "Info from ctor";
    }
    private void OnNewTestInfoCommand()
    {
        string newInfo = $"Info No. {++counter}";
        Debug.WriteLine($"{MethodBase.GetCurrentMethod().Name}: {nameof(TestInfoView)}=«{TestInfoView}» -> «{newInfo}»");
        TestInfoView = newInfo;
    }
}

private void BtnShow_Click(object sender, RoutedEventArgs e)
{
   Debug.WriteLine($"{MethodBase.GetCurrentMethod().Name}: {nameof(tct.TestInfo)}={tct.TestInfo}");
}

<!Tab Item Header Template>
<DataTemplate x:Key="CustomHeaderTemplate">

    <DockPanel LastChildFill="True">

        <TextBlock Text="{Binding FileName}"
                   VerticalAlignment="Center"
                   FontSize="14"/>

        <Button Command="{Binding DataContext.CloseTabCommand, RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
                CommandParameter="{Binding}"
                VerticalAlignment="Center"
                Height="22"
                Width="22"
                Background="SteelBlue"
                Margin="3,0,0,0">

            <Path Data="M1,9 L9,1 M1,1 L9,9"
                  Stroke="White"
                  StrokeThickness="2" />

        </Button>

    </DockPanel>

</DataTemplate>

<!Tab Item Style>
<Style TargetType="TabItem">

    <Setter Property="ContextMenu">
        <Setter.Value>
            <ContextMenu DataContext="{Binding Path=PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}" >

                <MenuItem Header="Close Tab"
                          Command="{Binding Source={StaticResource Proxy}, Path=Data.CloseTabCommand}"
                          CommandParameter="{Binding}"/>

                <MenuItem Header="Close All Tabs"
                          Command="{Binding Source={StaticResource Proxy}, Path=Data.CloseAllTabsCommand}"
                          CommandParameter="{Binding}"/>

                <MenuItem Header="Close All But This"
                          Command="{Binding Source={StaticResource Proxy}, Path=Data.CloseAllButThisTabCommand}"
                          CommandParameter="{Binding}"/>
            </ContextMenu>

        </Setter.Value>
    </Setter>

</Style>

<Window.Resources>

    <DataTemplate DataType="{x:Type vms:PlayerHostViewModel}">
        <vws:PlayerHostView/>
    </DataTemplate>

</Window.Resources>

<Border Grid.Row="1"
        Grid.Column="0"
        BorderThickness="1"
        BorderBrush="SteelBlue"
        Margin="5,0,0,5">

    <ItemsControl ItemsSource="{Binding Players}"
                    Margin="2">

        <ItemsControl.ItemsPanel>
            <ItemsPanelTemplate>
                <UniformGrid IsItemsHost="True"
                                Margin="2"/>
            </ItemsPanelTemplate>
        </ItemsControl.ItemsPanel>

    </ItemsControl>

</Border>

private void LoadPlayers()
{
    // If a player type and count are selected...
    if (SelectedPlayerInfo != null && SelectedPlayerCount > -1)
    {
        // For each player to add...
        for (int i = 0; i < SelectedPlayerCount + 1; i++)
        {
            // Create the player ActiveX control
            var playerAssembly = (IPlayer)Activator.CreateInstance(SelectedPlayerInfo.PlayerType);

            // Create the player host
            var player = new PlayerHostViewModel(playerAssembly, $"Player {i + 1}", LiveStream, DVRStream);

            // Add the player host to the Players list
            Players.Add(player);
        }
    }
}

public PlayerHostViewModel()
{
}
public PlayerHostViewModel(IPlayer player, string playerName, string liveStream, string dvrStream)
{
    Player = player;
    PlayerName = playerName;
    LiveStream = LiveStream;
    DVRStream = dvrStream;  
}

var player = new PlayerHostViewModel(playerAssembly, $"Player {i + 1}", LiveStream, DVRStream);

// Add the player host to the Players list
Players.Add(player);

<i:Interaction.Triggers>
    <i:EventTrigger EventName="AddingNewItem">
        <i:InvokeCommandAction Command="{Binding DataContext.NewItemAddedCommand, 
            RelativeSource={
                RelativeSource FindAncestor, AncestorType=Window}}"/>
    </i:EventTrigger>
</i:Interaction.Triggers>

<DataGrid Grid.Row="2"
          Grid.Column="0"
          ItemsSource="{Binding ColumnInfos}"
          HorizontalGridLinesBrush="LightGray"
          VerticalGridLinesBrush="LightGray"
          AutoGenerateColumns="False"
          CanUserAddRows="True"
          CanUserDeleteRows="True"
          CanUserReorderColumns="False"
          CanUserResizeColumns="False"
          CanUserSortColumns="False"
          BorderBrush="SteelBlue"
          BorderThickness="1"
          HeadersVisibility="Column"
          HorizontalScrollBarVisibility="Auto"
          VerticalScrollBarVisibility="Auto"
          VerticalAlignment="Stretch"
          Margin="5,0,5,5">

    <DataGrid.Resources>
        <local:BindingProxy x:Key="proxy" Data="{Binding IsColumnWidthVisibile}"/>
    </DataGrid.Resources>

    <DataGrid.Columns>

        <DataGridTemplateColumn>
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <Button Command="{Binding DeleteColumnCommand, RelativeSource={RelativeSource FindAncestor,
                                                                    AncestorLevel=1, AncestorType={x:Type Window}}}"
                            CommandParameter="{Binding}"
                            Margin="2"
                            Height="18"
                            Width="18"/>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
        </DataGridTemplateColumn>

        <DataGridTextColumn Header="Column Name"
                            Binding="{Binding ColumnName}"
                            Width="*"/>

        <DataGridTextColumn Header="Width"
                            Binding="{Binding ColumnWidth}"
                            Width="65"
                            Visibility="{Binding Data, Converter={StaticResource boolToVisibilityConverter}, Source={StaticResource proxy}}"/>

    </DataGrid.Columns>

</DataGrid>

System.InvalidCastException: 'Unable to cast object of type 'MS.Internal.NamedObject' to type 'WPFDataGrid.ColumnInfoEntity'.'