WPF中使用EventHandler更新UI内容

在WPF中，EventHandler类似于一套订阅与发布的操作。甲方提供一个event的回调注册入口让乙方来订阅自己发布的event。这么理解起来就是需要发布消息的一方定义event（就像是C语言里面定义了一个全局的回调函数指针变量），需要订阅event的一方就注册一个回调函数（就好像C语言里面对全局函数指针变量赋值）。

下面来一套演示代码，涉及两个窗口。

第一个是主窗口，提供一个textblock控件和一个按钮控件。代码如下：

<Window x:Class="EvtHdlrTest.SubEditWindow"
        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:EvtHdlrTest"
        mc:Ignorable="d"
        Title="SubEditWindow" Height="240" Width="320">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="4*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <TextBox x:Name="CtrlTextBox" Margin="5,5,5,5" Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2" VerticalScrollBarVisibility="Auto" Background="Yellow" FontSize="18" FontWeight="Bold"></TextBox>
        <Button x:Name="CtrlButtonCommit" Margin="5,5,5,5" Grid.Row="1" Grid.Column="0" Click="CtrlButtonCommit_Click" Background="Green">提交给主窗口</Button>
        <Button x:Name="CtrlButtonClose" Margin="5,5,5,5" Grid.Row="1" Grid.Column="1" Click="CtrlButtonClose_Click" Background="Red">关闭本窗口</Button>
    </Grid>
</Window>

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.Shapes;

namespace EvtHdlrTest
{
    /// <summary>
    /// SubEditWindow.xaml 的交互逻辑
    /// </summary>
    public partial class SubEditWindow : Window
    {
        public event EventHandler<string>? SubWindowTextChangedEventHandler;

        public SubEditWindow()
        {
            InitializeComponent();
        }

        public SubEditWindow(string s) : this()
        {
            CtrlTextBox.AppendText("从主窗口带来了如下字符串：\n" + s);
            CtrlTextBox.ScrollToEnd();
        }

        private void CtrlButtonCommit_Click(object sender, RoutedEventArgs e)
        {
            SubWindowTextChangedEventHandler?.Invoke(this, CtrlTextBox.Text);
            CtrlButtonCommit.IsEnabled = false;
        }

        private void CtrlButtonClose_Click(object sender, RoutedEventArgs e)
        {
            this.Close();
        }
    }
}

 

第二个是子窗口，提供一个textbox控件和两个按钮控件。代码如下：

<Window x:Class="EvtHdlrTest.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:EvtHdlrTest"
        mc:Ignorable="d"
        Title="MainWindow" Height="240" Width="400">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="4*"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <ScrollViewer x:Name="CtrlTextScroller"  Grid.Row="0" VerticalScrollBarVisibility="Visible">
            <TextBlock x:Name="CtrlTextBlock" Margin="5,5,5,5" />
        </ScrollViewer>
        <Button x:Name="CtrlButton" Margin="5,5,5,5" Grid.Row="1" Click="CtrlButton_Click">弹出新编辑窗</Button>
    </Grid>
</Window>

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 EvtHdlrTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            CtrlTextBlock.Text = "这些文字全部传给子窗口去编辑吧。";
        }

        private void CtrlButton_Click(object sender, RoutedEventArgs e)
        {
            string s = System.DateTime.Now.ToString("hh:mm:ss\n") + CtrlTextBlock.Text;
            SubEditWindow sw = new SubEditWindow(s);
            sw.SubWindowTextChangedEventHandler += TextFromSubWindow;
            sw.Show();
        }

        private void TextFromSubWindow(object? sender, string s)
        {
            CtrlTextBlock.Text = s;
            CtrlTextScroller.ScrollToBottom();
        }
    }
}

 

实测截图：

 

 

 

子窗口类里面定义了一个EventHandler成员变量：

namespace EvtHdlrTest
{
    public partial class SubEditWindow : Window
    {
        public event EventHandler<string>? SubWindowTextChangedEventHandler;
    }
}

主窗口中将子窗口的EventHandler成员变量追加了一个值：

string s = System.DateTime.Now.ToString("hh:mm:ss\n") + CtrlTextBlock.Text;
SubEditWindow sw = new SubEditWindow(s);
sw.SubWindowTextChangedEventHandler += TextFromSubWindow;
sw.Show();

最后子窗口点击按钮发出event：

private void CtrlButtonCommit_Click(object sender, RoutedEventArgs e)
{
    SubWindowTextChangedEventHandler?.Invoke(this, CtrlTextBox.Text);
    CtrlButtonCommit.IsEnabled = false;
}

主窗口监听到event执行了回调：

private void TextFromSubWindow(object? sender, string s)
{
    CtrlTextBlock.Text = s;
    CtrlTextScroller.ScrollToBottom();
}

整个Event的发布与回调就这样串起来了。