光标位置不会在根处停止：winforms RichTextBox

Question

I am trying to implement a command line utility with RichTextBox in user interface. I am trying to restrict the usage of Left and Right arrow keys similar to MS Dos command prompt window. My implementation should not allow user to cross the current root.

eg

If C:\\Test> is root, user should not be allowed to cross '>' with left arrow key.

Below is my code:

richTextbox1.KeyDown += OnKeyDown;
string root = "C:\Test>";

void OnKeyDown(object sender, KeyEventArgs e)
{
    switch (e.KeyCode)
    {
        case Keys.Left:
        case Keys.Right:
        {
            int lastline = richTextbox1.Lines.Length - 1;
            int first = richTextbox1.GetFirstCharIndexFromLine(lastline);
            int valid = first + root.Length + 1;

            if (richTextbox1.SelectionStart < valid )
            {
                richTextbox1.Select(valid, 0);
                richTextbox1.Invalidate();
            }
        }
        break;
    }
}

It works for case: C:\\Test>xyz : when user keeps pressing left arrow , s/he can not go beyond > character

Failing case: C:\\Test> : when user keeps pressing left arrow , s/he can go beyond > character and it stops at t

What is wrong with my code, I am not able to figure out?

Answer 1

Excellent, it works with e.Handled = true , working code as below: richTextbox1.KeyDown += OnKeyDown; string root = "C:\\Test>";

void OnKeyDown(object sender, KeyEventArgs e)
{
    switch (e.KeyCode)
    {
        case Keys.Left:
        case Keys.Right:
        {
            int lastline = richTextbox1.Lines.Length - 1;
            int first = richTextbox1.GetFirstCharIndexFromLine(lastline);
            int valid = first + root.Length + 1;

            if (richTextbox1.SelectionStart < valid )
            {
                //richTextbox1.Select(valid, 0);
                //richTextbox1.Invalidate();
                e.Handled = true;
            }
        }
        break;
    }
}