MultiTerm/MultiTerm.Wpf.CustomControl/MultiFormatDataView/MultiFormatDataView.cs

using MultiTerm.Core.ViewModel;
using System;
using System.Collections;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace MultiTerm.Wpf.CustomControl;

/// <summary>
/// Follow steps 1a or 1b and then 2 to use this custom control in a XAML file.
///
/// Step 1a) Using this custom control in a XAML file that exists in the current project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is 
/// to be used:
///
///     xmlns:MyNamespace="clr-namespace:MultiTerm.Wpf.CustomControl.MultiFormatDataView"
///
///
/// Step 1b) Using this custom control in a XAML file that exists in a different project.
/// Add this XmlNamespace attribute to the root element of the markup file where it is 
/// to be used:
///
///     xmlns:MyNamespace="clr-namespace:MultiTerm.Wpf.CustomControl.MultiFormatDataView;assembly=MultiTerm.Wpf.CustomControl.MultiFormatDataView"
///
/// You will also need to add a project reference from the project where the XAML file lives
/// to this project and Rebuild to avoid compilation errors:
///
///     Right click on the target project in the Solution Explorer and
///     "Add Reference"->"Projects"->[Browse to and select this project]
///
///
/// Step 2)
/// Go ahead and use your control in the XAML file.
///
///     <MyNamespace:MultiFormatDataView/>
///
/// </summary>
public class MultiFormatDataView : Control
{
    private const string itemsControlTemplateName = "itemsControl";
    private ItemsControl? itemsControl;

    #region Dependency Properties
    public static readonly DependencyProperty DataSourceProperty =
        DependencyProperty.Register("DataSource",
        typeof(IEnumerable), typeof(MultiFormatDataView),
        new PropertyMetadata(null, OnDataSourcePropertyChanged));

    /// <summary>
    /// .NET Property for DataSource.
    /// </summary>
    [Bindable(true)]
    public IEnumerable DataSource
    {
        get { return (IEnumerable)GetValue(DataSourceProperty); }
        set { SetValue(DataSourceProperty, value); }
    }

    #endregion

    static MultiFormatDataView()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(MultiFormatDataView), new FrameworkPropertyMetadata(typeof(MultiFormatDataView)));
    }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        // get itemsControl from template
        if (GetTemplateChild(itemsControlTemplateName) is ItemsControl itemsControl)
        {
            this.itemsControl = itemsControl;
        }
        else
        {
            throw new Exception($"Implementation fault, {itemsControlTemplateName} not found in template.");
        }

    }

    private static void OnDataSourcePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        // extract instance and guard null
        if (d is not MultiFormatDataView mfdv) { return; }
        // extract instance of new Value and guard null
        if (e.NewValue is not IEnumerable enumerable) { return; }

        // check if enumerable items are all of correct type
        foreach (var item in enumerable)
        {
            if (item is not DataViewModel) 
            { throw new ArgumentException($"{nameof(DataSourceProperty)} must be of type {nameof(DataViewModel)}"); }
        }

        // add group property
        CollectionView view = (CollectionView)CollectionViewSource.GetDefaultView(e.NewValue);
        PropertyGroupDescription groupDescription = new(nameof(DataViewModel.LineIdentifier));
        view.GroupDescriptions.Add(groupDescription);
    }
}