Question

How to get caret position (x, y) in the visible client zone in TextBox control? I need to add an auto complete feature to the text box.

I’ve found solution for WPF, but it can’t be applied in Silverlight.

Answer 1

public class AutoCompleteTextBox : TextBox
{
    public Point GetPositionFromCharacterIndex(int index)
    {
        if (TextWrapping == TextWrapping.Wrap) throw new NotSupportedException();

        var text = Text.Substring(0, index);

        int lastNewLineIndex = text.LastIndexOf('\r');

        var leftText = lastNewLineIndex != -1 ? text.Substring(lastNewLineIndex + 1) : text;

        var block = new TextBlock
                        {
                            FontFamily = FontFamily,
                            FontSize = FontSize,
                            FontStretch = FontStretch,
                            FontStyle = FontStyle,
                            FontWeight = FontWeight
                        };

        block.Text = text;
        double y = block.ActualHeight;

        block.Text = leftText;
        double x = block.ActualWidth;

        var scrollViewer = GetTemplateChild("ContentElement") as ScrollViewer;

        var point = scrollViewer != null
                        ? new Point(x - scrollViewer.HorizontalOffset, y - scrollViewer.VerticalOffset)
                        : new Point(x, y);
        point.X += BorderThickness.Left + Padding.Left;
        point.Y += BorderThickness.Top + Padding.Top;

        return point;
    }
}