FloatableDialog/POC/WpfApp1/DialogFrame.xaml.cs

using System.Windows.Controls;
using System.Windows.Input;

namespace WpfApp1
{
    using System.Windows;

    /// <summary>
    /// Interaction logic for DialogFrame.xaml
    /// </summary>
    public partial class DialogFrame
    {
        private Point? _mousePointOnClick;

        public DialogFrame(string title, string message)
        {
            InitializeComponent();
            this.TitleBlock.Text = title;
            this.MessageBlock.Text = message;
            SetMouseStatus();
        }

        private void CloseDialog_OnClick(object sender, RoutedEventArgs e)
        {
            DialogService.Instance.Remove(this);
        }

        private void NewDialog_OnClick(object sender, RoutedEventArgs e)
        {
            DialogService.Instance.Add(
                new DialogFrame("Child", $"Child dialog {DialogService.Instance.Dialogs.Count}")
            );
        }

        private void Border_OnMouseDown(object sender, MouseButtonEventArgs e)
        {
            var thisPosition = e.GetPosition(this);
            _mousePointOnClick = new Point(
                thisPosition.X - BorderTransform.X,
                thisPosition.Y - BorderTransform.Y
            );
            SetMouseStatus();
        }

        private void Border_OnMouseMove(object sender, MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed && _mousePointOnClick is { } pointOnClick)
            {
                var pos = e.GetPosition(this);
                BorderTransform.X = pos.X - pointOnClick.X;
                BorderTransform.Y = pos.Y - pointOnClick.Y;
            }
            SetMouseStatus();
        }

        private void Border_OnMouseUp(object sender, MouseButtonEventArgs e)
        {
            _mousePointOnClick = null;
            SetMouseStatus();
        }

        private void SetMouseStatus()
        {
            MouseStatus.Text =
                $"""PointOnClick:"{(_mousePointOnClick?.ToString() ?? "<null>")}", BorderTransform:"{BorderTransform.X:F1}:{BorderTransform.Y:F1}" """;
        }

        private void DialogFrame_OnKeyDown(object sender, KeyEventArgs e)
        {
            if (e.Key == Key.Escape)
            {
                DialogService.Instance.Remove(this);
            }
        }
    }
}