System.Windows.Forms.TextBoxBase.DeselectAll C# (CSharp) Method

		public void DeselectAll ()
		{
			SelectionLength = 0;
		}

        //Checks for valid input for Rx textboxes.  Checks the box passed in through "tb, "
        //using different criteria based on parameter the box represents (determined by "box").
        //Checks for valid ranges, does not check for valid increments.
        /// <summary>
        /// Checks for valid input for an Rx textbox
        /// </summary>
        /// <param name="tb">The box to check the contents of</param>
        /// <param name="box">The Rx parameter - Sphere, Cylinder, Axis or Add</param>
        /// <returns>True if the contents are valid, false otherwise</returns>
        /// <exception cref="System.FormatException">Thrown when the text is not a proper integer or real number</exception>
        private bool Rx_TextBox_Valid(TextBoxBase tb, RxBox box)
        {
            int pos = tb.Text.LastIndexOf('.');
            float val;

            if(box == RxBox.Axis)
            {
                if(tb.TextLength == 0) //Blank
                    tb.Text = "0";

                try { //Is the contents a valid integer?
                    val = Math.Abs(Convert.ToInt16(tb.Text));
                }
                catch {
                    return false;
                }

                tb.DeselectAll();
                tb.Text = val.ToString("0");

                //Checks for valid range
                if(val > AXIS_MAX_VALUE) {
                    return false;
                }
            }
            else //Sphere, Cylinder or Add
            {
                if(tb.TextLength == 0)
                    tb.Text = "0.00";

                try { //Is the contents a valid real number?
                    val = Convert.ToSingle(tb.Text);
                }
                catch {
                    return false;
                }

                tb.DeselectAll();
                if(pos > -1) //Handle decimal
                {
                    string ts = tb.Text.Substring(pos + 1);
                    if(ts == "2" || ts == "7")
                    {
                        if(val < 0)
                            val -= 0.05F;
                        else
                            val += 0.05F;
                    }
                }
                if(box == RxBox.Cyl)
                    val = -Math.Abs(val);
                tb.Text = val.ToString("0.00");

                //Checks for valid range
                if(box == RxBox.Sphere) {
                    if(val > SPHERE_MAX_VALUE) {
                        return false;
                    }
                } else if(box == RxBox.Cyl) {
                    if(-val > CYLINDER_MAX_VALUE) {
                        return false;
                    }
                } else {
                    if(val > ADD_MAX_VALUE) {
                        return false;
                    }
                }
            }
            return true;
        }