[2.0] Validating Text boxes

[urpalshu]

I am working on a Windows application in C#

I have two text boxes, to be validated with (txtFirstName and txtLastName)

Please could someone give me the syntax to use txtFirstName_Validating()
TO achieve the validation.
I have put the validation code inside the Button click event.

Please could you give me the best approach to validate the text boxes.

Thank you,
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private void txtFirstName_Validating(object sender, CancelEventArgs e)
{
if (string.IsNullOrEmpty(txtFirstName.Text))
{
MessageBox.Show("First Name required!");
}

}

private void btnLookUp_Click(object sender, EventArgs e)
{
if ((txtFirstName.Text == string.Empty) || (txtLastName.Text ==
string.Empty))
{
MessageBox.Show("Please enter the Name..");
}

}

[jmcilhinney]

There's no point using IsNullOrEmpty because the Text property of a control can NEVER return a null reference. You only have to check for an empty string. You would use something like this in the Validating event handler:

if (this.txtFirstName.Text == string.Empty)
{
    e.Cancel = true; //This line prevents the control losing focus.
    MessageBox.Show("Please enter a value for First Name.");
}

Note that this does not stop the user entering whitespace only. I would also recommend using code like this in the Leave event:

//Remove leading and trailing whitespace.
this.txtFirstName.Text = this.txtFirstName.Text.Trim();

The Leave event is raised before the Validating event so this will turn a whitespace only value into an empty string before validating.