如何让用户在页面的任何位置拖放WPF用户控件？

        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
           <ColumnDefinition Width="*"/>
           <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
       <Border Name="DragBorder" AllowDrop="True" BorderBrush="Black" BorderThickness="1" Grid.Column="0" Grid.Row="0" DragEnter="DragBorder_DragEnter" DragDrop="DragBorder_DragDrop">
            <TextBlock Text="Drag and drop here" FontSize="24" HorizontalAlignment="Center" VerticalAlignment="Center"/>
        </Border>
       <Button Name="DragButton" Content="Drag me" FontSize="24" Grid.Column="1" Grid.Row="0" DragEnter="DragButton_DragEnter" DragDrop="DragButton_DragDrop"/>
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls.Primitives;
using System.Windows.Documents;

namespace WpfApp1
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void DragBorder_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Text))
            {
                e.Effects = DragDropEffects.Copy;
            }
            else
            {
                e.Effects = DragDropEffects.None;
            }
        }

        private void DragBorder_DragDrop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Text))
            {
                string data = e.Data.GetData(DataFormats.Text) as string;
                TextBlock textBlock = new TextBlock();
                textBlock.Text = data;
                textBlock.FontSize = 24;
                textBlock.HorizontalAlignment = HorizontalAlignment.Center;
                textBlock.VerticalAlignment = VerticalAlignment.Center;
                DragBorder.Child = textBlock;
            }
        }

        private void DragButton_DragEnter(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Text))
            {
                e.Effects = DragDropEffects.Copy;
            }
            else
            {
                e.Effects = DragDropEffects.None;
            }
        }

        private void DragButton_DragDrop(object sender, DragEventArgs e)
        {
            if (e.Data.GetDataPresent(DataFormats.Text))
            {
                string data = e.Data.GetData(DataFormats.Text) as string;
                Button button = new Button();
                button.Content = data;
                button.FontSize = 24;
                DragBorder.Child = button;
            }
        }
    }
}