Validation Using the KeyPress Event in a Windows Application

Create a Windows application and design a form in it as per your requirements.

Now most of the time the user needs validation in a Windows application, so before the user enters a wrong value (such as instead of text the user enters an integer) we can validate it using an event and some sort of coding.

For example in the following screen, a KeyPress event is created for the TextBox.



Now Create one Class Validation.cs and write the following code in it:

public void charonly(KeyPressEventArgs e)
{
if (Char.IsNumber(e.KeyChar) || Char.IsSymbol(e.KeyChar) || Char.IsWhiteSpace(e.KeyChar) || Char.IsPunctuation(e.KeyChar))
{
MessageBox.Show("Only Char are allowed");
e.Handled = true;
}
}

public void digitonly(KeyPressEventArgs e)
{
try
{
if (!(char.IsDigit(e.KeyChar) || char.IsControl(e.KeyChar) || char.IsPunctuation(e.KeyChar)))
{
e.Handled = true;
MessageBox.Show("Enter only digit and decimal point.", "Alert!");
}
}
catch { }
}

Now call these two methods as per validation type (char or int) from the TextBox KeyPress Event:

validation v = new validation();

private void textBox5_KeyPress(object sender, KeyPressEventArgs e)
{
v.digitonly(e); // allowing interger only
}

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
v.charonly(e); // allowing character only
}