Throw an exception by getting the selected text via UIA

Question

I have a.NET 8.0 WPF application that wants to get user-selected text through UIA, but an exception was thrown when retrieving words. Here is my code

private void MainWindow_Loaded(object sender, RoutedEventArgs e)

{

_mouseHook = new MouseHook();

_mouseHook.MouseDown += MouseHook_MouseDown;

_mouseHook.MouseUp += MouseHook_MouseUp;

_mouseHook.Register();

}

private void MouseHook_MouseUp(object? sender, MouseHookEventArgs e)

{

var text = GetControlText();

selectedTBK.Text = text;

Debug.WriteLine($"Selected text: {text}");

}

private void MouseHook_MouseDown(object? sender, MouseHookEventArgs e)

{

}

private string GetControlText()

{

try

{

    IntPtr hwnd = GetForegroundWindow();

    AutomationElement rootElement = AutomationElement.FromHandle(hwnd);

    AutomationElement textBox = rootElement.FindFirst(TreeScope.Descendants,

        new PropertyCondition(AutomationElement.ControlTypeProperty, ControlType.Edit));

    if (textBox != null && textBox.TryGetCurrentPattern(TextPattern.Pattern, out object pattern))

    {

        TextPattern textPattern = (TextPattern)pattern;

        if (textPattern.DocumentRange != null)

        {

            TextPatternRange[] selection = textPattern.GetSelection();

            if (selection.Length > 0)

            {

                string selectedText = selection[0].GetText(-1);

                Debug.WriteLine($"Selected Text: {selectedText}");

                return selectedText;

            }

            else

            {

                Debug.WriteLine("No text selected.");

                return string.Empty;

            }

        }

    }

    else

    {

        Debug.WriteLine("Text control not found or does not support TextPattern.");

        return string.Empty;

    }

}

catch (AccessViolationException ex)

{

    Debug.WriteLine(ex.Message);

}

catch (ElementNotAvailableException ex)

{

    Debug.WriteLine(ex.Message);

}

catch (Exception ex)

{

    Debug.WriteLine(ex.Message);

}

return string.Empty;

}

Answer 1

Hi, @华 张. Welcome to Microsoft Q&A. 

I used the following code to successfully obtain the value of the text. You could refer to it.

if (textBox != null && textBox.TryGetCurrentPattern(TextPattern.Pattern, out object pattern))
{
       TextPattern textPattern = (TextPattern)pattern;
       if (textPattern.DocumentRange != null)
       {
             string text = textPattern.DocumentRange.GetText(-1);
             Debug.WriteLine($"Selected Text: {text}");
             return text;
       }
       else
       {
             Debug.WriteLine("No text selected.");
             return string.Empty;
       }
}

Complete code(Here I use the Click event of Button instead of the MouseHook_MouseUp event of MouseHook) MainWindow.xaml

<Grid x:Name="MyGrid">
    <Grid.RowDefinitions>
        <RowDefinition/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <TextBox x:Name="MyText" Text="HAHA"  Background="GreenYellow" Height="50"></TextBox>
    <TextBlock x:Name="selectedTBK" Grid.Row="1" Background="DimGray" Height="50"></TextBlock>
    <Button Grid.Row="1" Height="50" Width="200" Content="Click Me!" Margin="0,120,0,0" Click="Button_Click"></Button>
</Grid>

MainWindow.xaml.cs

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        public IntPtr GetForegroundWindow()
        {
            return new WindowInteropHelper(this).Handle;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            var text = GetControlText();
            selectedTBK.Text = text;

            Debug.WriteLine($"Selected text: {text}");
        }

        private string GetControlText()
        {
            try
            {
                IntPtr hwnd = GetForegroundWindow();

                AutomationElement rootElement = AutomationElement.FromHandle(hwnd);
                AutomationElement textBox = rootElement.FindFirst(TreeScope.Descendants,new PropertyCondition(AutomationElement.ControlTypeProperty, ControlType.Edit));
                if (textBox != null && textBox.TryGetCurrentPattern(TextPattern.Pattern, out object pattern))
                {
                    TextPattern textPattern = (TextPattern)pattern;
                    if (textPattern.DocumentRange != null)
                    {
                        string text = textPattern.DocumentRange.GetText(-1);
                        Debug.WriteLine($"Selected Text: {text}");
                        return text;
                    }
                    else
                    {
                        Debug.WriteLine("No text selected.");
                        return string.Empty;
                    }
                }
                else
                {
                    Debug.WriteLine("Text control not found or does not support TextPattern.");
                    return string.Empty;
                }
            }
            catch (AccessViolationException ex)
            {
                Debug.WriteLine(ex.Message);
            }

            catch (ElementNotAvailableException ex)
            {
                Debug.WriteLine(ex.Message);
            }

            catch (Exception ex)
            {
                Debug.WriteLine(ex.Message);
            }
            return string.Empty;
        }
    }

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