GetCharIndexFromPosition () for last char

Question

I want to get a substring under a cursor in a RichTextBox.

private void richTextBox1_MouseDown(object sender, MouseEventArgs e)
{
    if (e.Clicks == 1 && e.Button == MouseButtons.Left)
    {
        string wholeText = richTextBox1.Text;
        // Obtain the character index where the user clicks on the control. 
        int positionBegin = richTextBox1.GetCharIndexFromPosition(new Point(e.X, e.Y));
        SelectedText = wholeText.Substring(positionBegin);
    }

For example, if I type a line World, then place the cursor between land d, the substring should be d. My code still works, however, if I put the cursor at the end of the line, it still returns d.

I expect that in this case it will return empty. This seems like a mistake. See http://www.pcreview.co.uk/forums/problem-getcharindexfromposition-t4037504.html

Answer 1

How is that a mistake? If you look at the description, it will get the closest character. , , . , , , .

, RichTextBox, , . -, , , : .

//...
string originalText = richTextBox1.Text;
richTextBox1.Text += " ";

//Your code to get the index and substring

//Return the textbox to its original state
richTextBox1.Text = originalText;
richTextBox1.SelectionLength = 0;
richTextBox1.SelectionStart = positionBegin;

, , , . , GetCharIndexFromPosition(Point pt), , , .

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EDIT: ( )

RichTextBox, , :

public override int GetCharIndexFromPosition(Point pt) {
    NativeMethods.POINT wpt = new NativeMethods.POINT(pt.X, pt.Y);
    int index = (int)UnsafeNativeMethods.SendMessage(new HandleRef(this, Handle), NativeMethods.EM_CHARFROMPOS, 0, wpt);

    string t = this.Text;
    //This bit is stopping you from getting an index outside the length of the text
    if (index >= t.Length) {
        index = Math.Max(t.Length - 1, 0);
    }
    return index;
}

"" , , , , , :

public static class RichTextBoxExtensions
{
    private const int EM_CHARFROMPOS = 0x00D7;

    public static int GetTrueIndexPositionFromPoint(this RichTextBox rtb, Point pt)
    {
        POINT wpt = new POINT(pt.X, pt.Y);
        int index = (int)SendMessage(new HandleRef(rtb, rtb.Handle), EM_CHARFROMPOS, 0, wpt);

        return index;
    }

    [DllImport("User32.dll", EntryPoint = "SendMessage", CharSet = CharSet.Auto)]
    private static extern IntPtr SendMessage(HandleRef hWnd, int msg, int wParam, POINT lParam);
}

[StructLayout(LayoutKind.Sequential)]
internal class POINT
{
    public int x;
    public int y;

    public POINT()
    {
    }

    public POINT(int x, int y)
    {
        this.x = x;
        this.y = y;
    }
}

! GetCharIndexFromPosition GetTrueIndexPositionFromPoint .

Answer 2

() .
, . , , . . , , . , . 'GetCharIndexFromPosition()' 'GetPositionFromCharIndex()'. , , , , .

private void transparentPanel_Click(object sender, System.EventArgs e)
        {
            var mouseEventArgs = e as MouseEventArgs;
            if (mouseEventArgs.Button == MouseButtons.Left)
            {
                // If currently in text editing mode
                if (m_currentSelectedControl == e_SelectedControl.TEXT)
                {
                    Point capturedPoint = new Point(mouseEventArgs.X, mouseEventArgs.Y);
                    int charIndex = richTextBox.GetCharIndexFromPosition(capturedPoint);
                    int lastChar = richTextBox.TextLength;
                    Point lastCharPoint = richTextBox.GetPositionFromCharIndex(lastChar);

                    if (lastCharPoint.X == capturedPoint.X ||
                        lastCharPoint.Y < capturedPoint.Y)
                    {
                        charIndex++;
                    }

                    richTextBox.SelectionStart = charIndex;
                    richTextBox.SelectionLength = 0;
                    richTextBox.Select();
                    transparentPanel.Refresh();
                }
            }
        }

Answer 3

. GetCharIndexFromPosition :

If the specified location is not within the client control rectangle or is outside the last character in the control, return Value is the index of the last character.