创建子窗体，子窗体向父窗体传值

项目如下图

然后建立我们的界面代码和后台代码如下:
一、MainPage.xaml与MainPage.xaml.cs代码如下

MainPage.xaml代码

MainPage.xaml.cs代码 

代码 using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SLChildWindow
{
    public partial class MainPage : UserControl
    {
        private PopupWindow popupWindow;

        public MainPage()
        {
            InitializeComponent();
            popupWindow = new PopupWindow();
            popupWindow.Closed += new EventHandler(PopupWindow_Closed);
        }


        private void PopupWindow_Closed(object sender, EventArgs e)
        {
            if ((bool)popupWindow.DialogResult)
            {
                dialogResult.Text = "用户在子窗口按下的是确定按钮.";
                lblReturnTxt.Content = popupWindow.txtInput.Text.ToString();
            }
            else
            {
                dialogResult.Text = "用户在子窗口按下的是取消按钮";
            }
        }

        private void Button_Click1(object sender, RoutedEventArgs e)
        {
            popupWindow.Title = "按下按钮一";
            popupWindow.SetMessage("你按下的是按钮一.");
            popupWindow.txtInput.Text = "";
            popupWindow.Show();
        }

        private void Button_Click2(object sender, RoutedEventArgs e)
        {
            popupWindow.Title = "按下按钮二";
            popupWindow.SetMessage("你按下的是按钮二.");
            popupWindow.txtInput.Text = "";
            popupWindow.Show();
        }
    }

    }

二、PopupWindow.xaml与PopupWindow.xaml.cs代码如下

PopupWindow.xaml代码

代码 <controls:ChildWindow x:Class="SLChildWindow.PopupWindow"
           xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
           xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
           xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
           Width="400" Height="300"
           Title="PopupWindow" xmlns:dataInput="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.Input">
    <Grid x:Name="LayoutRoot" Margin="2">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <TextBlock x:Name="Message" Text="" TextWrapping="Wrap"/>
        
        <Button x:Name="CancelButton" Content="取消" Click="CancelButton_Click" Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,0,0" Grid.Row="1" />
        <Button x:Name="OKButton" Content="确定" Click="OKButton_Click" Width="75" Height="23" HorizontalAlignment="Right" Margin="0,12,79,0" Grid.Row="1" />
       
        <dataInput:Label Height="20" HorizontalAlignment="Left" Margin="46,48,0,0" Name="label1" VerticalAlignment="Top" Width="100" Content="请输入文本" />
        <TextBox  x:Name="txtInput"  Height="60" HorizontalAlignment="Left" Margin="46,82,0,0"  VerticalAlignment="Top" Width="280" />
    </Grid>
</controls:ChildWindow>

PopupWindow.xaml.cs代码

代码 using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SLChildWindow
{
    public partial class PopupWindow : ChildWindow
    {
        public PopupWindow()
        {
                  
            InitializeComponent();
            this.Loaded += new RoutedEventHandler(PopupWindow_Loaded);
        }

        void PopupWindow_Loaded(object sender, RoutedEventArgs e)
        {
            this.GotFocus += new RoutedEventHandler(PopupWindow_GotFocus);    
        }

        void PopupWindow_GotFocus(object sender, RoutedEventArgs e)
        {
           txtInput.Focus();
           GotFocus -= PopupWindow_GotFocus;
        }

        public void SetMessage(string theMessage)
        {
            Message.Text = theMessage;

        }

        private void OKButton_Click(object sender, RoutedEventArgs e)
        {
            this.DialogResult = true;
            
        }

        private void CancelButton_Click(object sender, RoutedEventArgs e)
        {
            this.DialogResult = false;
        }

    }
}

运行效果如下: