I've read a lot threads on the email lists about how to set up an
automatically vertically scrolling view similar to a terminal view.
I want new text to appear at the bottom of a textview and the scroll
bar position to remain at the bottom, unless the user has moved it to
look at some text. Basically I want a window that displays text
output that behaves and performs exactly like the Terminal
application or the Run Log in XCode.
I have attempted to do this by appending my text data to the
textStorage mutableString. To control the scroll bar position, I use
the scrollToVisibleRange method. Unfortunately, I have read about
and experienced the performance hit when using this method (It is
supposedly O(N) for the number of lines).
I know that this can be done because I see that the Run Log in Xcode
and the Terminal have this behavior without getting the spinning ball
when it updates more than 10 lines a second. Can someone give me a
hint at a more efficient way to achieve this behavior?
Here my current implementation for the textview:
- (void)updateReceiverConsole:(NSNotification *)aNotification
{
float scrollPos = [[receiverScroll verticalScroller] floatValue]; //
Get the current scrollbar position
NSString *aLogMessage = [aNotification object];
if(!aLogMessage==nil) //Append the new text to the textStorage
mutableString
{
[[[receiverConsole textStorage] mutableString ]
appendString:aLogMessage];
}
// Delete the old lines of text to keep the text a set number of lines
if([[[receiverConsole textStorage] paragraphs] count]>50)
{
[[receiverConsole textStorage] deleteCharactersInRange:NSMakeRange
(0, [[[[receiverConsole textStorage] paragraphs] objectAtIndex:0]
length])];
}
// if the scrollbar *was all the way at the bottom before the new
text was appended,
// then scroll down to the bottom
if( scrollPos == 1.0 )
{
NSRange range;
range = NSMakeRange ([[receiverConsole string] length], 0);
[receiverConsole scrollRangeToVisible: range]; //This method is O
(N) for the number of lines!
}
}
Cheers,
Chris Woodruff
Jet Propulsion Laboratory
M/S: 138-206
4800 Oak Grove Dr.
Pasadena, CA 91109
818-354-2412
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