wpf.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Shapes;
using System.Windows.Media;

class Test
{
    static void move(UIElement sh, double x, double y)
    {
        Canvas.SetLeft(sh, x);
        Canvas.SetTop(sh, y);
    }

    static Canvas canvas;
    static UIElement elem;
    static Point click = new Point();
    static Point orig = new Point();

    static void down(UIElement el, MouseButtonEventArgs e)
    {
        elem = el;
        orig = new Point(Canvas.GetLeft(el), Canvas.GetTop(el));
        click = e.GetPosition(canvas);
        canvas.CaptureMouse();
    }

    [STAThread]
    static void Main()
    {
        var w = new Window { Title = "Test", Width = 256, Height = 256 };
        w.Show();

        canvas = new Canvas();
        w.Content = canvas;

        var r = new Rectangle { Width = 40, Height = 40 };
        move(r, 20, 60);
        r.Stroke = new SolidColorBrush(Colors.Black);
        r.Fill = new SolidColorBrush(Colors.Yellow);
        canvas.Children.Add(r);

        var tb = new TextBlock { Text = "abcdefg", FontSize = 24 };
        move(tb, 20, 30);
        canvas.Children.Add(tb);

        r.MouseDown += (sender, e) => down(r, e);
        tb.MouseDown += (sender, e) => down(tb, e);
        canvas.MouseMove += (sender, e) =>
        {
            if (elem != null)
            {
                var p = e.GetPosition(canvas);
                move(elem, orig.X + p.X - click.X, orig.Y + p.Y - click.Y);
            }
        };
        canvas.MouseUp += (sender, e) =>
        {
            elem = null;
            canvas.ReleaseMouseCapture();
        };
        new Application().Run(w);
    }
}