Way to obtain the word cursor is on, in WPF RichTextBox Control

Question

I would like to know how I can get the word that current cursor is on, in WPF RichTextBox. I am aware that RichTextBox has Selection Property. However, this only gives me the text that is highlighted in the RichTextBox. Instead I would like to know the word the cursor is on even if the whole word is not highlighted.

Any tips are appreciated.

Answer 1

Attach this function to an arbitrary RichTextBox, now called testRTB, and see Output window for results:

private void testRTB_MouseUp(object sender, MouseButtonEventArgs e)
{
        TextPointer start = testRTB.CaretPosition;  // this is the variable we will advance to the left until a non-letter character is found
        TextPointer end = testRTB.CaretPosition;    // this is the variable we will advance to the right until a non-letter character is found

        String stringBeforeCaret = start.GetTextInRun(LogicalDirection.Backward);   // extract the text in the current run from the caret to the left
        String stringAfterCaret = start.GetTextInRun(LogicalDirection.Forward);     // extract the text in the current run from the caret to the left

        Int32 countToMoveLeft = 0;  // we record how many positions we move to the left until a non-letter character is found
        Int32 countToMoveRight = 0; // we record how many positions we move to the right until a non-letter character is found

        for (Int32 i = stringBeforeCaret.Length - 1; i >= 0; --i)
        {
            // if the character at the location CaretPosition-LeftOffset is a letter, we move more to the left
            if (Char.IsLetter(stringBeforeCaret[i]))
                ++countToMoveLeft;
            else break; // otherwise we have found the beginning of the word
        }


        for (Int32 i = 0; i < stringAfterCaret.Length; ++i)
        {
            // if the character at the location CaretPosition+RightOffset is a letter, we move more to the right
            if (Char.IsLetter(stringAfterCaret[i]))
                ++countToMoveRight;
            else break; // otherwise we have found the end of the word
        }



        start = start.GetPositionAtOffset(-countToMoveLeft);    // modify the start pointer by the offset we have calculated
        end = end.GetPositionAtOffset(countToMoveRight);        // modify the end pointer by the offset we have calculated


        // extract the text between those two pointers
        TextRange r = new TextRange(start, end);
        String text = r.Text;


        // check the result
        System.Diagnostics.Debug.WriteLine("[" + text + "]");
}

Change Char.IsLetter(...) to Char.IsLetterOrDigit(...) or whatever else appropriately depending on whether you wish to keep digits as well.

Tip: extract this into an extension method in a separate assembly to access it whenever needed.

Answer 2

OK so in order to solve this I brute forced it.

I used curCaret.GetTextInRun(LogicalDirection.Backward) and curCaret.GetTextInRun(LogicalDirection.Forward)

along with preCaretString.LastIndexOf(" ") and postCaretString.IndexOf(" ") plus other dividers that separates word and got the substrings.

Eventually I added the first half of string and second half of string to obtain the currently cursored word.

I bet there are cleverer way of doing this but at least this solved the problem

Answer 3

You can get the current position of the cursor via CaretPosition.

Unfortunately there is no easy way to get the characters to the left/right of the caret position. The only way I know of to get text out of a RichTextBox is in this answer, which is a bit convoluted. But it will accomplish what is necessary.