IsNumeric - Web Developer

[Madhumati]

I want to make a webshop in a college project. It will have a text box where you can choose how many you want to order from the list that appears. My problem lies at a point where if a user enters a letter instead of a number, I want that an error message should appear. However I do not get the error on the page. How do I do this? Can not find it with google, unfortunately.

[opaper]

int number;
if ( Integer.TryParse(textbox.Text, out number) {
    // All is well
} else {
    //This is not an integer, error handling here
}

[void]

You can also use Ajax control toolkit's filtered textbox extender. Here is the code that you can use to create a popup with the error to the user if the validation fails:

private void MessageBox(string message)
{
    this.RegisterStartupScript(this, this.GetType(), "err_msg", "alert('" + message + "');", true);
}

[kelfro]

Although I use an event and regex so that it is not possible to use other than numbers and backspace, if the user tries to type anything, nothing happens.

private void textBox_privatestoresell_quantity_KeyPress(object sender, KeyPressEventArgs e)
{
    if ((!System.Text.RegularExpressions.Regex.IsMatch(e.KeyChar.ToString(), "\\d+"))&&(!System.Text.RegularExpressions.Regex.IsMatch(e.
KeyChar.ToString(), "\b" )))
        e.Handled = true;

}

[Katty]

I created a text box for this once.

using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;
using System.Text.RegularExpressions;

namespace orsaDB
{
    public class CheckedTextEditor : TextBox
    {
            protected Regex m_reg;
            protected string m_reg_exp;
            protected bool m_ignore_case;
            protected bool m_allow_invalid_text;

            [DefaultValue(false)]
            public bool IgnoreCase
            {
                    get
                    {
                            return m_ignore_case;
                    }
                    set
                    {
                            m_ignore_case = value;
                            RebuildRegex();
                    }
            }

            [DefaultValue(false)]
            public bool AllowInvalidText
            {
                    get
                    {
                            return m_allow_invalid_text;
                    }
                    set
                    {
                            m_allow_invalid_text = value;
                    }
            }
            [DefaultValue(true)]
            public bool IsTextValid
            {
                    get
                    {
                            if ( m_reg != null )
                                    return ValidateText( Text );
                            else
                                    return true;
                    }
            }

            protected void RebuildRegex()
            {
                    m_reg = new Regex(m_reg_exp, m_ignore_case ? RegexOptions.IgnoreCase : RegexOptions.None);
            }
            [DefaultValue("")]
            public string RegularExpression
            {
                    get
                    {
                            return m_reg_exp;   
                    }
                    set
                    {
                            m_reg_exp = value;
                            m_reg = new Regex( m_reg_exp );

                            RebuildRegex();
                    }
            }

            public CheckedTextEditor()
            {
                    m_reg_exp = "";
                    m_reg = null;
            }

            protected override void onkeypress( KeyPressEventArgs e )
            {
                    base.onkeypress( e );
                    if ( e.KeyChar != (char)8 && !m_allow_invalid_text)
                    {
                            string text = Text + e.KeyChar;

                            e.Handled = !ValidateText( text );
                    }
            }
            protected bool ValidateText( string text )
            {
                    Match m = m_reg.Match( text );
                    return (m.Index == 0) && (m.Length == text.Length);
            }

            protected override void OnTextChanged( EventArgs e )
            {
                    ForeColor = IsTextValid ? SystemColors.WindowText : Color.Red;
                    base.OnTextChanged( e );
            }
                /// <summary> 
                /// Required designer variable.
                /// </summary>
                private System.ComponentModel.IContainer components = null;

                /// <summary> 
                /// Clean up any resources being used.
                /// </summary>
                /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
                protected override void Dispose( bool disposing )
                {
                        if ( disposing && ( components != null ) )
                        {
                                components.Dispose();
                        }
                        base.Dispose( disposing );
                }

                #region Component Designer generated code

                /// <summary> 
                /// Required method for Designer support - do not modify 
                /// the contents of this method with the code editor.
                /// </summary>
                private void InitializeComponent()
                {
                        components = new System.ComponentModel.Container();
                }

                #endregion

    }
}