Question

I’m making a textbox to autoscroll to the end when text is added. However I wanted the option to not scroll the textbox when the mouse is over the textbox. I’ve done all that, but when the user selects text and the textbox receives an event to update the text, everything goes haywire.

Here’s what I’m working with:

---

<TextBox Text="{Binding ConsoleContents, Mode=OneWay}" TextWrapping="Wrap" 
    IsReadOnly="True" ScrollViewer.VerticalScrollBarVisibility="Visible" 
    TextChanged="TextBox_TextChanged" MouseEnter="TextBox_MouseEnterLeave"
    MouseLeave="TextBox_MouseEnterLeave" AllowDrop="False" Focusable="True" 
    IsUndoEnabled="False"></TextBox>

---

private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        TextBox textBox = sender as TextBox;
        if (textBox == null) return;

        // ensure we can scroll
        if (_canScroll)
        {
            textBox.Select(textBox.Text.Length, 0); //This was an attempt to fix the issue
            textBox.ScrollToEnd();
        }
    }

private void TextBox_MouseEnterLeave(object sender, MouseEventArgs e)
    {
        TextBox textBox = sender as TextBox;

        // Don't scroll if the mouse is in the box
        if (e.RoutedEvent.Name == "MouseEnter")
        {
            _canScroll = false;
        }
        else if (e.RoutedEvent.Name == "MouseLeave") 
        {
            _canScroll = true;
        }
    }

To further explain what haywire means, when the textbox receives and propertychanged event it sets the text and scrolls down to the end if the mouse is not hovering over it. If the mouse is hovering over it does not scroll. But if I select text and the textbox recives the propertychanged event the content gets updated, but the box does not scroll down. This is expected. The problem is that my selection then goes from where the cursor currently is to the top of the text. If I remove the cursor from the box, it continues fine but once the cursor returns, the box gets stuck at the top and cannot scroll down. I thought it might have been the cursor so I try to move it to the end but that solves nothing.

Any ideas?!

I’ve been ripping my hair out! Thanks!

Answer 1

Well it took all morning but here’s how to do it:

<TextBox Text="{Binding ConsoleContents, Mode=OneWay}" 
         TextWrapping="Wrap" IsReadOnly="True" ScrollViewer.VerticalScrollBarVisibility="Visible" TextChanged="TextBox_TextChanged" 
         MouseEnter="TextBox_MouseEnterLeave" MouseLeave="TextBox_MouseEnterLeave" SelectionChanged="TextBox_SelectionChanged" AllowDrop="False" Focusable="True" 
         IsUndoEnabled="False"></TextBox>

---

public partial class ConsoleView : UserControl
{
    private bool _canScroll;

    // saves
    private int _selectionStart;
    private int _selectionLength;
    private string _selectedText;

    public ConsoleView(ConsoleViewModel vm)
    {
        InitializeComponent();
        this.DataContext = vm;

        _canScroll = true;
    }


    private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        TextBox textBox = sender as TextBox;
        if (textBox == null) return;

        // ensure we can scroll
        if (_canScroll)
        {
            // set the cursor to the end and scroll down
            textBox.Select(textBox.Text.Length, 0);
            textBox.ScrollToEnd();

            // save these so the box doesn't jump around if the user goes back in
            _selectionLength = textBox.SelectionLength;
            _selectionStart = textBox.SelectionStart;
        }
        else if (!_canScroll)
        {

            // move the cursor to where the mouse is if we're not selecting anything (for if we are selecting something the cursor has already moved to where it needs to be)
            if (string.IsNullOrEmpty(_selectedText))
            //if (textBox.SelectionLength > 0)
            {
                textBox.CaretIndex = textBox.GetCharacterIndexFromPoint(Mouse.GetPosition(textBox), true);
            }
            else
            {
                textBox.Select(_selectionStart, _selectionLength); // restore what was saved
            }

        }
    }


    private void TextBox_MouseEnterLeave(object sender, MouseEventArgs e)
    {
        TextBox textBox = sender as TextBox;
        if (textBox == null) return;

        // Don't scroll if the mouse is in the box
        if (e.RoutedEvent.Name == "MouseEnter")
        {
            _canScroll = false;
        }
        else if (e.RoutedEvent.Name == "MouseLeave")
        {
            _canScroll = true;
        }

    }


    private void TextBox_SelectionChanged(object sender, RoutedEventArgs e)
    {
        TextBox textBox = sender as TextBox;
        if (textBox == null) return;

        // save all of the things
        _selectionLength = textBox.SelectionLength;
        _selectionStart = textBox.SelectionStart;
        _selectedText = textBox.SelectedText; // save the selected text because it gets destroyed on text update before the TexChanged event.

    }

}