wpf - .NET Framework 4.7.1中的AutomationProperties.LiveSetting在WPF中不起作用

我有一个TextBlock，我想从屏幕阅读器跟踪该控件，并且只要在代码中为该控件设置了新值，屏幕阅读器就应该读出新文本。这可以从MSDN LINK中提到的.NET Framework 4.7.1的WPF中获得。

但是，我总是获得 AutomationPeer 值的 null 。我在代码中缺少什么？我做对了吗？请帮忙。

XMAL

      <Window x:Class="WPFAccessibility.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:WPFAccessibility"
                mc:Ignorable="d"
                Title="WPFAccessibility" Height="450" Width="800">
            <Grid>

                <TextBlock Name="MyTextBlock" AutomationProperties.LiveSetting="Assertive">My initial text</TextBlock>

                <Button Name="Save" Content="Save" HorizontalAlignment="Left" VerticalAlignment="Top" Width="75" Margin="50,321,0,0" Height="49" Click="Save_Click"/>

            </Grid>
        </Window>

代码

 private void Save_Click(object sender, RoutedEventArgs e)
        {
            // Setting the MyTextBlock text to some other value and screen
            // reader should notify to the user
            MyTextBlock.Text = "My changed text";
            var peer = UIElementAutomationPeer.FromElement(MyTextBlock);
           // I am always getting peer value null
            peer.RaiseAutomationEvent(AutomationEvents.LiveRegionChanged);
        }

最佳答案

使用CreatePeerForElement方法为UIElementAutomationPeer创建一个TextBlock:

private void Save_Click(object sender, RoutedEventArgs e)
{
    MyTextBlock.Text = "My changed text";
    var peer = UIElementAutomationPeer.FromElement(MyTextBlock);
    if (peer == null)
        peer = UIElementAutomationPeer.CreatePeerForElement(MyTextBlock);
    peer.RaiseAutomationEvent(AutomationEvents.LiveRegionChanged);
}