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 -, , );
             }

             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 + , , );
             }
         }

         //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, , );
             }
         }
     }
 }

 <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>