if (txtContainerNo.TextLength < 4) { e.Handled = !(char.IsUpper(e.KeyChar) || e.KeyChar == (char)Keys.Back); } else { e.Handled = !(char.IsDigit(e.KeyChar) || e.KeyChar == (char)Keys.Back); }
if ((e.KeyCode >= Keys.A && e.KeyCode <= Keys.Z) || (e.KeyCode >= Keys.D0 && e.KeyCode <= Keys.D9)) { charCount++; } else if (e.KeyCode == Keys.Back) { charCount--; } else { } if (charCount <= 4) { if (e.KeyCode >= Keys.A && e.KeyCode <= Keys.Z && e.Shift && e.KeyCode == Keys.Back) { } else { e.SuppressKeyPress = true; } } else if (charCount > 4) { if (!(e.KeyCode >= Keys.A && e.KeyCode <= Keys.Z && e.KeyCode != Keys.Back)) { } else { e.SuppressKeyPress = true; }
^[a-zA-Z]{4}\d{7}$
var
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