Validation in Asp.net Windows Application

static void Main() 
        {
            Application.Run(new SimpleValidation());
        }

        private void txtName_Validating(object sender, System.ComponentModel.CancelEventArgs e)
        {
            if (((TextBox)sender).Text == "")
            {
                MessageBox.Show("You must enter a first and last name.", "Invalid Input", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                e.Cancel = true;
            }
        }

windows application 
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textbox validation 
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mail id validation 
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private void textBox1_Validating(object sender, 
System.ComponentModel.CancelEventArgs e) 
{ 
string errorMsg; 
if(!ValidEmailAddress(textBox1.Text, out errorMsg)) 
{ 
// Cancel the event and select the text to be corrected by the user. 
e.Cancel = true; 
textBox1.Select(0, textBox1.Text.Length); 

// Set the ErrorProvider error with the text to display. 
this.errorProvider1.SetError(textBox1, errorMsg); 
} 
} 

private void textBox1_Validated(object sender, System.EventArgs e) 
{ 
// If all conditions have been met, clear the ErrorProvider of errors. 
errorProvider1.SetError(textBox1, ""); 
} 
public bool ValidEmailAddress(string emailAddress, out string errorMessage) 
{ 
// Confirm that the e-mail address string is not empty. 
if(emailAddress.Length == 0) 
{ 
errorMessage = "e-mail address is required."; 
return false; 
} 

// Confirm that there is an "@" and a "." in the e-mail address, and in the correct order. 
if(emailAddress.IndexOf("@") > -1) 
{ 
if(emailAddress.IndexOf(".", emailAddress.IndexOf("@") ) > emailAddress.IndexOf("@") ) 
{ 
errorMessage = ""; 
return true; 
} 
} 

errorMessage = "e-mail address must be valid e-mail address format.\n" + 
"For example 'someone@example.com' "; 
return false; 
} 



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textbox validation accepts number only 
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private void textBox3_Validating(object sender, CancelEventArgs e) 
{ 
try 
{ 
int numberEntered = int.Parse(textBox3.Text); 
if (numberEntered < 1 || numberEntered > 10) 
{ 
e.Cancel = true; 
MessageBox.Show("You have to enter a number between 1 and 10"); 
} 
} 
catch (FormatException) 
{ 
e.Cancel = true; 
MessageBox.Show("You need to enter an integer"); 
} 
} 



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only numbers and a dot 
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private void textBox2_TextChanged(object sender, EventArgs e) 
{ 

if (!(string.IsNullOrEmpty(textBox2.Text))) 
{ 

char[] chars = textBox2.Text.ToCharArray(); 
for (int i = 0; i < textBox2.Text.Length; i++) 
{ 
int code; 
code = Convert.ToInt16(chars ); 
if (!((!(code > 58 || code < 48)) || (code == 68) || (code == 78) || (code == 35) || (code == 46))) 
{ 
textBox2.Text = textBox2.Text.Remove(i, 1); 
textBox2.SelectionStart = textBox2.Text.Length; 
} 
} 
} 

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e-mail validation 

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private void textBox1_Validating(object sender, CancelEventArgs e) 
{ 
System.Text.RegularExpressions.Regex rEMail = new System.Text.RegularExpressions.Regex(@"^[a-zA-Z][\w\.-]{2,28}[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$"); 
if (textBox1.Text.Length > 0) 
{ 
if (!rEMail.IsMatch(textBox1.Text)) 
{ 
MessageBox.Show("E-Mail expected", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); 
textBox1.SelectAll(); 
e.Cancel = true; 
} 
} 
} 

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TEXTBOX ONLY ACCEPTS CHARACTERS 
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private void textBox4_KeyPress(object sender, KeyPressEventArgs e) 
{ 
if ((e.KeyChar >= 65 && e.KeyChar <= 90) || (e.KeyChar >= 97 && e.KeyChar <= 122) || e.KeyChar == 32 || e.KeyChar == 8) 
{ 
e.Handled = false; 
} 
else 
{ 
MessageBox.Show("Invalid Input"); 
e.Handled = true; 
} 
} 
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