WPF Popup：移入显示，移出隐藏

1.看一下Demo的效果；

2.直接上代码：

 MainWindow.xaml：

<Window x:Class="PopupDemo.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:PopupDemo"
  mc:Ignorable="d"
  Title="诗词" Height="400" Width="500">
    <Grid>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="9*"></RowDefinition>
                <RowDefinition Height="1*"></RowDefinition>
            </Grid.RowDefinitions>
            <Grid>
                <Button x:Name="BtnPopup" Height="80" Width="120" Padding="2 " MouseEnter="BtnPopup_MouseEnter" MouseLeave= "BtnPopup_MouseLeave" >
                    <Grid >
                        <TextBlock>杜甫《绝句》</TextBlock>
                        <local:PopupNonTopmost x:Name="pop1" StaysOpen="True" HorizontalOffset="0" VerticalOffset="0" 
                        PlacementTarget="{Binding ElementName=BtnPopup}" MouseLeave="pop1_MouseLeave">
                            <Grid Height="120" Width="150">
                                <Border BorderThickness="1" Background="White" BorderBrush="#015eea">
                                    <StackPanel Orientation="Vertical" HorizontalAlignment="Center">
                                        <TextBlock Margin="5" Text="两只黄鹂鸣翠柳" TextDecorations="Underline" />
                                        <TextBlock Margin="5" Text="一行白鹭上青天" TextDecorations="Underline" />
                                        <TextBlock Margin="5" Text="窗含西岭千秋雪" TextDecorations="Underline" />
                                        <TextBlock Margin="5" Text="门泊东吴万里船" TextDecorations="Underline" />
                                    </StackPanel>
                                </Border>
                            </Grid>
                        </local:PopupNonTopmost>
                    </Grid>
                </Button>
            </Grid>
            <Grid Grid.Row="1">
                <Label Name="label1" VerticalAlignment="Center" HorizontalAlignment="Center" FontFamily="Calibri" Content="https://www.cnblogs.com/yellow3gold/"
            FontSize="14" FontWeight="Bold" FontStyle="Italic" Foreground="Red"></Label>
            </Grid>
        </Grid>
    </Grid>
</Window>

MainWindow.xaml.cs

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

namespace PopupDemo
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void pop1_MouseLeave(object sender, MouseEventArgs e)
        {
            pop1.IsOpen = false;
        }

        private void BtnPopup_MouseEnter(object sender, MouseEventArgs e)
        {
            pop1.IsOpen = false;
            pop1.IsOpen = true;
        }

        private void BtnPopup_MouseLeave(object sender, MouseEventArgs e)
        {
            var point = Mouse.GetPosition(pop1);
            if (point.X < 0 || point.Y < 0)
                pop1.IsOpen = false;
            if (point.X > BtnPopup.Height && point.Y > 1)
                pop1.IsOpen = false;
        }
    }
}

PopupNonTopmost.cs

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Controls.Primitives;
using System.Windows.Interop;

namespace PopupDemo
{
    public class PopupNonTopmost : Popup
    {
        public static DependencyProperty TopmostProperty = Window.TopmostProperty.AddOwner(
          typeof(PopupNonTopmost),
          new FrameworkPropertyMetadata(false, OnTopmostChanged));

        public bool Topmost
        {
            get { return (bool)GetValue(TopmostProperty); }
            set { SetValue(TopmostProperty, value); }
        }

        private static void OnTopmostChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            (obj as PopupNonTopmost).UpdateWindow();
        }

        protected override void OnOpened(EventArgs e)
        {
            UpdateWindow();
        }

        private void UpdateWindow()
        {
            var hwnd = ((HwndSource)PresentationSource.FromVisual(this.Child)).Handle;
            RECT rect;

            if (GetWindowRect(hwnd, out rect))
            {
                SetWindowPos(hwnd, Topmost ? -1 : -2, rect.Left, rect.Top, (int)this.Width, (int)this.Height, 0);
            }
        }

        #region P/Invoke imports & definitions

        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int Left;
            public int Top;
            public int Right;
            public int Bottom;
        }

        [DllImport("user32.dll")]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);

        [DllImport("user32", EntryPoint = "SetWindowPos")]
        private static extern int SetWindowPos(IntPtr hWnd, int hwndInsertAfter, int x, int y, int cx, int cy, int wFlags);

        #endregion
    }
}