Popup 是一个用于显示临时性内容的控件，它可以在应用程序的其他内容之上显示一个弹出窗口。它通常用于实现下拉菜单、工具提示、通知消息等功能。

主要属性为：

Child：获取或设置 Popup控件的内容。
IsOpen：获取或设置一个值，该值指示Popup 是否可见
Placement:获取或设置 Popup 控件打开时的控件方向，并指定Popup 控件在与屏幕边界重叠时的控件行为
PlacementTarget：获取或设置当打开 Popup 控件时该控件相对于其放置的元素。
PopupAnimation：获取或设置Popup 控件的打开和关闭动画。
StaysOpen：获取或设置一个值，该值指示当 Popup 控件焦点不再对准时，是否关闭该控件。

 

案例：

PopupBox.xaml

<Popup x:Class="WPF.Common.Dialog.PopupBox"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:WPF.Common.Dialog"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Grid>
        <Border x:Name="border" Background="Gray" CornerRadius="8" MinHeight="35" Width="400" Height="100">
            <TextBlock TextWrapping="WrapWithOverflow"
                       Foreground="White"
                       Margin="10"
                       FontSize="18"
                       HorizontalAlignment="Center"
                       VerticalAlignment="Center"
                       Text="{Binding Path=Message,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=local:PopupBox},UpdateSourceTrigger=PropertyChanged}"/>
        </Border>
    </Grid>
</Popup>

PopupBox.xaml.cs

 /// <summary>
    /// PopupBox.xaml 的交互逻辑
    /// </summary>
    public partial class PopupBox : Popup
    {
        private static PopupBox dialog = new PopupBox();
        private static DispatcherTimer timer = new DispatcherTimer();

        public PopupBox()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 弹出对话框
        /// </summary>
        /// <param name="message">消息</param>
        /// <param name="owner">所属窗体对象</param>
        /// <param name="seconds">对话框隐藏倒计时（秒）</param>
        public static void Show(string message, Window owner = null, int seconds = 1)
        {
            try
            {
                Application.Current.Dispatcher.Invoke(new Action(() =>
                {
                    if (owner == null)
                    {
                        owner = Application.Current.MainWindow;
                    }

                    dialog.Message = message;
                    dialog.PlacementTarget = owner;
                    dialog.Placement = PlacementMode.Center;
                    dialog.StaysOpen = true;
                    dialog.AllowsTransparency = true;
                    dialog.VerticalOffset = owner.ActualHeight / 3;
                    dialog.Opacity = 0.9;
                    dialog.IsOpen = true;

                    timer.Tick -= Timer_Tick;
                    timer.Tick += Timer_Tick;
                    timer.Interval = new TimeSpan(0, 0, seconds);
                    timer.Start();

                }));
            }
            catch
            {
            }
        }

        private static void Timer_Tick(object sender, EventArgs e)
        {
            timer.Stop();
            Task.Run(() =>
            {
                try
                {
                    for (int i = 0; i < 100; i++)
                    {
                        Thread.Sleep(5);
                        if (Application.Current == null) return;
                        Application.Current.Dispatcher.Invoke(() =>
                        {
                            dialog.Opacity -= 0.01;
                        });
                    }

                    Application.Current.Dispatcher.Invoke(() =>
                    {
                        dialog.IsOpen = false;
                        dialog.Message = string.Empty;
                    });
                }
                catch
                {

                }
            });
        }



        /// <summary>
        /// 依赖属性--透明度
        /// </summary>
        public new double Opacity
        {
            get { return (double)GetValue(OpacityProperty); }
            set { SetValue(OpacityProperty, value); }
        }

        public static new readonly DependencyProperty OpacityProperty =
            DependencyProperty.Register("Opacity", typeof(double), typeof(PopupBox), new PropertyMetadata(1.0, new PropertyChangedCallback(OnOpacityPropertyChangedCallback)));

        private static void OnOpacityPropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (!(d is PopupBox box)) return;
            if (!(e.NewValue is double v)) return;
            box.border.Opacity = v;//赋值新的透明度
        }


        /// <summary>
        /// 依赖属性--消息
        /// </summary>
        public string Message
        {
            get { return (string)GetValue(MessageProperty); }
            set { SetValue(MessageProperty, value); }
        }

        public static readonly DependencyProperty MessageProperty =
            DependencyProperty.Register("Message", typeof(string), typeof(PopupBox), new PropertyMetadata(string.Empty));





    }