How do I make screen readers read my WPF message similarly to how they read Win32 MessageBox?

Question

We have a WPF desktop application which needs to show some custom message windows. I am having trouble getting them to be read aloud properly by screen readers such as JAWS from Freedom Scientific.

I want to achieve the same behavior as when showing a system message box. For comparison, System.Windows.MessageBox.Show("my message", "My Caption); is announced by JAWS as "My caption dialog. My message. OK Button". This is perfect.

When my message windows are opened (containing only a TextBlock and OK Button), the window title is announced and the OK button is announced as having focus but the TextBlock message is not announced.

Here's a simple test application which shows the issue. Our real app has icons and other status text, of course.

<Window x:Class="Jaws_MessageBox_Test.MyMessageBox"
        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:Jaws_MessageBox_Test"
        mc:Ignorable="d"
        Title="MyMessageBox" Height="300" Width="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height="Auto"></RowDefinition>
        </Grid.RowDefinitions>
        <TextBlock x:Name="mainLabel" Grid.Row="0">Hi there, this is a test to see if JAWS will read the main textbloc when shown.</TextBlock>
        <Button Grid.Row="1" Margin="5" HorizontalAlignment="Right" Padding="10,0,10,0"  IsDefault="True" x:Name="closeButton" Click="closeButton_Click">_Close</Button>
    </Grid>
</Window>

When I show this using:

var mb = new MyMessageBox();
mb.ShowDialog();

The screen reader announces: "MyMessageBox. Close Button" so it's not reading the TextBlock like the system message box does.

What I've found using the Windows SDK inspect and accevent tools is that

• The system message box accessibility type is 'Dialog' but the WPF dialog's accessibility type is 'Window'. This might matter. There is no UI Automation Control Type of Dialog https://msdn.microsoft.com/en-us/library/ms749005(v=vs.110).aspx . Is this a bug or limitation in WPF perhaps?

• I have tried setting various 'AutomationProperties' attached properties on my window so that the AutomationPeer will have better info but none of those are read when the ShowDialog runs.

• Since TextBlock cannot receive input focus, there's no way to even get the text read by tabbing. I temporarily use a read-only TextBox instead to get focus but the experience is still wrong and our blind users should not have to tab around just to have a simple status message read to them.

• As part of the experimenting, I also tried creating my own derived AutomationPeer for the message window but none of the Core method content is read automatically when the dialog is launched. The automation child list does have the title bar object listed as the first child whereas that's the last child for the system message box though I don't see a way to change that right now.

I'd greatly appreciate any help for creating a WPF-based custommessage box with full, proper accessibility for blind users.

Answer 1

You have to tell the automation API that your Window is a MessageBox. To do that add this code to your Window

protected override AutomationPeer OnCreateAutomationPeer()
{
    return new MessageBoxWindowAutomationPeer(this);
}

and add this class to your project

public class MessageBoxWindowAutomationPeer : WindowAutomationPeer
{
    private const string WC_DIALOG = "#32770";

    public MessageBoxWindowAutomationPeer(Window owner)
        : base(owner)
    {
    }

    protected override string GetClassNameCore()
    {
        return WC_DIALOG;
    }

    protected override string GetLocalizedControlTypeCore()
    {
        return "Dialogfeld";
    }

    protected override bool IsContentElementCore()
    {
        return true;
    }

    protected override bool IsControlElementCore()
    {
        return true;
    }
}

As we don't need localization in our app "DialogFeld" is the german localized control type. Localizing that one is the part you would have to find out by yourself. ;-)