private void TextBox1_TextChanged(object sender, EventArgs e) { if (_ignoreTextChange) { return; } if (textBox1.Text.Length < 1) { return; } _ignoreTextChange = true; // Toggles this event off to edit the value of the TextBox. var originalKeywords = textBox1.Text.Split('\n'); textBox1.Text = Filtering.JoinStrings(Filtering.FilterUniques(originalKeywords)); _ignoreTextChange = false; // Toggles the TextChanged event back on since the text has been properly modified. }