Call Method C#

Question

Hello, I’m with a project in progress where I have an employee registration screen. I need to leave the edge of the TextBox red if there is something wrong with filling it out.
I tried in many ways and none gave the result I hoped.
I found this code on the Internet, but I don’t know how to call the method on condition.

Method

private void DrawRectangle(Graphics g, Rectangle rect, float penWidth)
{
    using (Pen pen = new Pen(SystemColors.ControlDark, penWidth))
    {
        float shrinkAmount = pen.Width / 2;
        g.DrawRectangle(
            pen,
            rect.X + shrinkAmount,
            rect.Y + shrinkAmount,
            rect.Width - penWidth,
            rect.Height - penWidth);
    }
}

Condition if field is empty.

if (txtNomeFuncionario.Text == string.Empty)
{
    MessageBox.Show("O campo Nome parece estar vazio.");
    txtNomeFuncionario.BorderStyle = BorderStyle.None;
    // Preciso chamar o método DrawRetangle aqui
}

The method and the condition are in the same class, excuse the lack of knowledge, but I am new in this language.

@EDIT With the code below I almost got the result I wanted, but it was not perfect as the original border.

txtNomeFuncionario.BorderStyle = BorderStyle.None;
this.CreateGraphics().DrawRectangle(new Pen(Color.Red, 2f),
    txtNomeFuncionario.Location.X,
    txtNomeFuncionario.Location.Y,
    txtNomeFuncionario.Width,
    txtNomeFuncionario.Height);

Result of the above code
Image 1

Image 2

Thanks in advance.

Answer 1

Try this:

private void button1_Click(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(textBox1.Text))
    {
        textBox1.BorderStyle = BorderStyle.None;
        this.CreateGraphics().DrawRectangle(new Pen(Color.Red, 2.0f), textBox1.Location.X, textBox1.Location.Y, textBox1.Width, textBox1.Height);
    }            
}

Note that CreateGraphics() is a form method containing the textBox1.

1. I removed the Borders;
2. I drew a rectangle exactly in place of the edges;

Image with other alternatives as reported in the comment:

Answer 2

You have to use Paint’s Event Form. It must be something like that:

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        if (String.IsNullOrEmpty(txtNomeFuncionario.Text))
            DrawRectangle(e.Graphics, txtNomeFuncionario.DisplayRectangle, 1);
    }

    private void DrawRectangle(Graphics g, Rectangle rect, float penWidth)
    {
        using (Pen pen = new Pen(SystemColors.ControlDark, penWidth))
        {
            float shrinkAmount = pen.Width / 2;
            g.DrawRectangle(
                pen,
                rect.X + shrinkAmount,
                rect.Y + shrinkAmount,
                rect.Width - penWidth,
                rect.Height - penWidth);
        }
    }