Grid move

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 WpfApplication1
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Binding binding = new Binding();
            binding.Source = main_grid;
            binding.Path = new PropertyPath("Margin");
            binding.Mode = BindingMode.TwoWay;
            binding.Converter = new MarginConverter();
            binding.ConverterParameter = main_grid.Width;
            sub_grid.SetBinding(Grid.MarginProperty, binding);
        }

        public class MarginConverter : IValueConverter
        {

            public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                Thickness margin = (Thickness)value;
                double width = (double)parameter;
                return new Thickness(margin.Left + width, margin.Top -30, 0, 0);
            }

            public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                Thickness margin = (Thickness)value;
                double width = (double)parameter;
                return new Thickness(margin.Left - width, margin.Top + 30, 0, 0);
            }
        }

        //选中控件的鼠标位置偏移量
        Point targetPoint;

        private void canvas_MouseDown(object sender, MouseButtonEventArgs e)
        {
            var targetElement = e.Source as IInputElement;
            if (targetElement != null)
            {
                targetPoint = e.GetPosition(targetElement);
                //开始捕获鼠标
                targetElement.CaptureMouse();
            }
        }

        private void canvas_MouseUp(object sender, MouseButtonEventArgs e)
        {
            //取消捕获鼠标
            Mouse.Capture(null);
        }

        private void canvas_MouseMove(object sender, MouseEventArgs e)
        {
            //确定鼠标左键处于按下状态并且有元素被选中
            var targetElement = Mouse.Captured as Grid;
            if (e.LeftButton == MouseButtonState.Pressed && targetElement != null)
            {
                var pCanvas = e.GetPosition(canvas);
                //设置最终位置
                targetElement.Margin = new Thickness(pCanvas.X - targetPoint.X, pCanvas.Y - targetPoint.Y, 0, 0);
            }
        }
    }
}

<Window x:Class="WpfApplication1.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:local="clr-namespace:WpfApplication1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Canvas>
        <Viewbox Stretch="Fill">
            <Grid x:Name="canvas" Height="350" Width="525">
                <Grid x:Name="main_grid" Height="50" Width="80" Background="Yellow" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="100,100,0,0" PreviewMouseMove="canvas_MouseMove" PreviewMouseLeftButtonDown="canvas_MouseDown" PreviewMouseLeftButtonUp="canvas_MouseUp">
                    <Border BorderBrush="Black" BorderThickness="1" ></Border>
                </Grid>
                <Grid x:Name="sub_grid" Height="30" Width="30" Background="LightBlue" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="180,70,0,0" PreviewMouseMove="canvas_MouseMove" PreviewMouseLeftButtonDown="canvas_MouseDown" PreviewMouseLeftButtonUp="canvas_MouseUp">
                    <Border BorderBrush="Black" BorderThickness="1"></Border>
                </Grid>
            </Grid>
        </Viewbox>
    </Canvas>
</Window>