UWP TextBox - Focus on selection

Question

I have a .NET UWP TextBox with a good deal of text, and I want to search for a word in it. When I click on the button to start my search, it will find the first occurrence of this word. When I click again, it will find the second, like ctrl+f in Notepad).

I want to get focus on the found world, but when is text is long enough that there is a scrollbar in, it will not bring the found word into view.

This is a screengrab of the screen in this state, showing how I must resize the window to see the found word.

Here is my code for searching (textarea is of type TextBox):

private void Find(string text)
    {
        textarea.Focus(FocusState.Programmatic);
        var start = textarea.SelectionStart + textarea.SelectionLength;
        var found =  (bool)checkboxFindCaseSensitive.IsChecked ? textarea.Text.IndexOf(text, start) : textarea.Text.IndexOf(text, start, StringComparison.CurrentCultureIgnoreCase);
        if (found == -1)
        {
            textarea.SelectionStart = 0;
            found = (bool)checkboxFindCaseSensitive.IsChecked ? textarea.Text.IndexOf(text, start) : textarea.Text.IndexOf(text, start, StringComparison.CurrentCultureIgnoreCase);
            if (found == -1) return;
        }
        textarea.SelectionStart = found;
        textarea.SelectionLength = text.Length;
    }

I have already tried to put textarea.Focus(FocusState.Programmatic); at the end of method as well as textarea.Focus(FocusState.Pointer);, but neither helped.

UPDATE:

I've found that it's focusing correctly, but to the last found word (to position, where is the cursor before find next word), not to the currently found word.

So I need to update focus to current SelectionStart, not to the last. Any ideas? I have already tried to change SelectionStart again, replace text and update layout - nothing helps.

Answer 1

What you can do is to measure the height of your text until the index, and resize the textbox accordingly.

private static float GetTextHeightUntilIndex(TextBox textBox, int index)
    {
        var height = 0;
        var textBuffer = textBox.Text;

        // Remove everything after `index` in order to measure its size
        textBox.Text = textBuffer.Substring(0, index);
        textBox.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
        var height = textBox.DesiredSize().Height;

        // Put the full text back
        textBox.Text = textBuffer;

        return height;
    }

private void Find(string text)
    {
        textarea.Focus(FocusState.Programmatic);
        var start = textarea.SelectionStart + textarea.SelectionLength;
        var found =  (bool)checkboxFindCaseSensitive.IsChecked ? textarea.Text.IndexOf(text, start) : textarea.Text.IndexOf(text, start, StringComparison.CurrentCultureIgnoreCase);
        if (found == -1)
        {
            textarea.SelectionStart = 0;
            found = (bool)checkboxFindCaseSensitive.IsChecked ? textarea.Text.IndexOf(text, start) : textarea.Text.IndexOf(text, start, StringComparison.CurrentCultureIgnoreCase);
            if (found == -1) return;
        }
        textarea.SelectionStart = found;
        textarea.SelectionLength = text.Length;

        // -------------------

        var cursorPosInPx = GetTextHeightUntilIndex(textarea, found);

        // First method: resize your textbox to the selected word
        textarea.Height = cursorPosInPx; 

        // Second method: scroll the textbox
        var grid = (Grid)VisualTreeHelper.GetChild(textarea, 0);
        for (var i = 0; i <= VisualTreeHelper.GetChildrenCount(grid) - 1; i++)
        {
            object obj = VisualTreeHelper.GetChild(grid, i);
            if (obj is ScrollViewer)
                ((ScrollViewer)obj).ChangeView(null, cursorPosInPx, null, true);
        }
    }

Be careful however, for the first method, depending on whatlayout your textbox is, resizing the control may have an unwanted effect or no effect at all.