I'll make a guess as I see that you may be using that RichTextBox (RTB) as a log.
Updating via the Text property gets slower as the existing RTB data length increases and the AppendText method is much better.
However the AppendText method also suffers from a similar slow down and it is best to create a group of text within a StringBuilder and then make one call to AppendText.
private void UpdateMethods() {
String OneLineOfData = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" + Environment.NewLine;
const Int32 LinesToAdd = 10000;
for (Int32 i = 0; i < LinesToAdd; i++) {
rtb.Text += OneLineOfData;
}
for (Int32 i = 0; i < LinesToAdd; i++) {
rtb.AppendText(OneLineOfData);
}
StringBuilder sb = new StringBuilder(OneLineOfData.Length * LinesToAdd);
for (Int32 i = 0; i < LinesToAdd; i++) {
sb.Append(OneLineOfData);
}
rtb.AppendText(sb.ToString());
}
Alan.