winforms - C# Get cursor line in RichTextBox

Question

In C#, I have a RichTextBox, and I want to get the current line of the cursor. Every answer I've found says to use:

int currentLine = richTextBox1.GetLineFromCharIndex(richTextBox1.SelectionStart);

However, richTextBox1.SelectionStart only updates when you make changes to the text. If you move the cursor with the arrow keys, it does not update (I've verified this by printing SelectionStart as I move around).

How do I get the current line of the cursor, in a way that tracks it even if you use the arrow keys to move the cursor around?

I'm using VS2012 in Win8.

Edit: terrybozzio's answer showed the problem. For anyone else with this problem, you can't put the code in richTextBox1_TextChanged. You need to put it in richTextBox1_SelectionChanged.

Answer 1

First you need to get selectionstart,If there isn't any selected text, the value returned is the position of the caret(with offset in characters from the start of the text),then you call getlinefromcharindex and pass that value,place it in the selectionchanged event and even with arrow keys moving the caret position it will update:

private void richTextBox1_SelectionChanged(object sender, EventArgs e)
{
    int index = richTextBox1.SelectionStart;
    int line = richTextBox1.GetLineFromCharIndex(index);
    label1.Text = "cursor at line " + line.ToString();
}