Question

I put two textbox in user control in C# winform.txtFrom and txtTo. I want to compare two textbox.text and if txtTo is less than txtFrom , error provider are shown.
how do I do?

Answer 1

You don’t compare something with error provider. Error provider only shows that control has an error associated with control.

• Add ErrorProvider component to your form
• Compare txtFrom.Text and txtTo.Text (e.g. during Validating event)
• If text is less (I don’t know what less means for you), then call errorProvider1.SetError(txtTo, "Text is less than txtFrom"), otherwise call errorProvider1.SetError(txtTo, "")

How to do comparison:

errorProvider1.SetError(txtFrom, "");
errorProvider1.SetError(txtTo, "");

int fromValue;
int toValue;

if (!Int32.TryParse(txtFrom.Text, out fromValue)
{
    errorProvider1.SetError(txtFrom, "Integer number required");
    return;
}

if (!Int32.TryParse(txtTo.Text, out toValue)
{
    errorProvider1.SetError(txtTo, "Integer number required");
    return;
}

if (toValue < fromValue)
{
    errorProvider1.SetError(txtTo, "To is less than From");
    return;
}

Consider also using NumericUpDown control to avoid text parsing stuff.