Changing button name with dynamic textbox event handler

Question

I need when pressing Mouse Right click creating a textbox in midle of button. And when pressing enter key in my textbox to changing button name as textbox given Text;

Here is my code:

 TextBox txt;
 private void c_MouseDown(object sender, MouseEventArgs e)
    {
    if (e.Button == MouseButtons.Right)
        {
            ss = sender as Button;
            Point location = ss.Location;
            int xLocation = ss.Location.X;
            int yLocation = ss.Location.Y;

            txt = new TextBox();
            txt.Name = "textBox1";
            txt.Text = "Add Text";

            txt.Location = new Point(xLocation - 10, yLocation + 20);
            Controls.Add(txt);
            txt.Focus();
            txt.BringToFront();

            txt.KeyDown += txt_KeyDown;
        }
    }


    private void txt_KeyDown(object sender, KeyEventArgs e)
    {

        if (e.KeyCode == Keys.Enter)
        {
            ss = sender as Button;
            ss.Name = txt.Text;
        }

    }

I get error Object reference not set to an instance of an object.

Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — , Dec 28 '16 at 09:33
In the `txt_KeyDown` event, the `sender` is the textbox, not the button. So this line `ss = sender as Button;` sets `ss` to null. — Zohar Peled, Dec 28 '16 at 09:36

Zohar Peled · Accepted Answer · 2016-12-28T10:16:08.093

One way to solve it is to hold a reference to the button in the Tag property of the textbox:

TextBox txt;
private void c_MouseDown(object sender, MouseEventArgs e)
{
if (e.Button == MouseButtons.Right)
    {
        ss = sender as Button;
        Point location = ss.Location;
        int xLocation = ss.Location.X;
        int yLocation = ss.Location.Y;

        txt = new TextBox();
        txt.Name = "textBox1";
        txt.Text = "Add Text";
        txt.Tag = ss;

        txt.Location = new Point(xLocation - 10, yLocation + 20);
        Controls.Add(txt);
        txt.Focus();
        txt.BringToFront();

        txt.KeyDown += txt_KeyDown;
    }
}


private void txt_KeyDown(object sender, KeyEventArgs e)
{

    if (e.KeyCode == Keys.Enter)
    {
        ss = (sender as TextBox).Tag as Button;
        ss.Name = txt.Text;
        Controls.Remove(txt);
    }

}

It works thank you ! But how can i Close my txt after enter key? — Dim111, Dec 28 '16 at 10:11
Glad to help. I've added a call to `Controls.Remove(txt);` at the end of the `txt_KeyDown` event handler. — Zohar Peled, Dec 28 '16 at 10:16

Changing button name with dynamic textbox event handler

1 Answers1