Consider this scenario.  You have an NSTextView scrolled to the end and as new text appears in the window, you want to see the new text immediately, so it scrolls to the very bottom for you.  Now you decide you want to read some text further up, so you scroll the text upwards.  As you’re reading, new text gets appended and suddenly it all scrolls down to the bottom again, causing you to lose your place.

We’re going to assume the NSTextView is named textView.  Imaginative, I know.

Usually we could append some coloured text and scroll to the end with something like this…

- (void)writeText:(NSString *)text
{
	// append some blue text
	NSDictionary *attribs = [NSDictionary dictionaryWithObject:[NSColor blueColor] forKey:NSForegroundColorAttributeName];
	NSAttributedString *stringToAppend = [[NSAttributedString alloc] initWithString:text attributes:attribs];
	[[textView textStorage] appendAttributedString:stringToAppend];
	[stringToAppend release];

	// scroll to the end
	NSRange range = NSMakeRange ([[textView string] length], 0);
	[textView scrollRangeToVisible: range];
}

Assuming you’ve just dropped the NSTextView on to a window or view from Interface Builder, the NSTextView will have been placed inside of an NSScrollView.  That NSScrollView can be queried to determine if the scrollbar was already at the bottom.  You should do this before you append any text.

	bool scrollToEnd = YES;

	id scrollView = (NSScrollView *)textView.superview.superview;
	if ([scrollView isKindOfClass:[NSScrollView class]]) {
		if ([scrollView hasVerticalScroller]) {
			if (textView.frame.size.height > [scrollView frame].size.height) {
				if (1.0f != [scrollView verticalScroller].floatValue)
					scrollToEnd = NO;
			}
		}
	}

Firstly we default scrollToEnd to YES. Next we check the NSTextView’s superview’s superview to make sure it is actually an NSScrollView. If it is, and if it has a vertical scrollbar and our NSTextView is large enough to require scrolling, then we look at how far the scroll bar has moved. This can be done by looking at its floatValue.

The floatValue can range from 0.0 to 1.0. If a scrollbar is at the very bottom (or all the way over to the right if it’s horizontal) then it’s floatValue will be 1.0.

Here’s the complete code.

- (void)writeText:(NSString *)text
{
	// determine if we should scroll to the end
	bool scrollToEnd = YES;

	id scrollView = (NSScrollView *)textView.superview.superview;
	if ([scrollView isKindOfClass:[NSScrollView class]]) {
		if ([scrollView hasVerticalScroller]) {
			if (textView.frame.size.height > [scrollView frame].size.height) {
				if (1.0f != [scrollView verticalScroller].floatValue)
					scrollToEnd = NO;
			}
		}
	}

	// append some coloured text
	NSDictionary *attribs = [NSDictionary dictionaryWithObject:[NSColor blueColor] forKey:NSForegroundColorAttributeName];
	NSAttributedString *stringToAppend = [[NSAttributedString alloc] initWithString:text attributes:attribs];
	[[textView textStorage] appendAttributedString:stringToAppend];
	[stringToAppend release];

	if (scrollToEnd) {
		// scroll to the end
		NSRange range = NSMakeRange ([[textView string] length], 0);
		[textView scrollRangeToVisible: range];
	}
}

I was using my laptop and connecting to my iMac across the network and browsing through its files. The connection would occasionally drop and it would sometimes show folder contents as empty when I knew for a fact they were not. The option to share the screen would also disappear at random and occasionally the whole iMac would disappear from Finder.

Much cursing was done.

The problem turned out to have an odd solution. I noticed it was connecting to the shares using the Windows smb protocol rather than AFP (Apple’s File Sharing Protocol) so I disabled smb on the iMac. Now everything works fine. At least until I try to access the iMac from Windows anyway….

sudo nano /etc/hosts

The problem with that is that I have a nice looking graphical operating system here and although I love the fact that it uses unix under the bonnet, I really much prefer to edit my files in TextEdit rather than a console based application like nano.  I could use the open command like this:

sudo open -a TextEdit /etc/hosts

but then I just have my default user privileges and I can’t save it, even though I used sudo!  The correct solution is actually to use:

sudo open -a /Applications/TextEdit.app/Contents/MacOS/TextEdit /etc/hosts

The reason for this is that an application in OS X is actually a folder that contains all the necessary files and resources that it uses, and the executable file itself is buried in a couple of subfolders.  Neat and tidy, but a bit of a pain to type in the terminal!

I decided I’d make my own sudo / open script which I creatively named sopen.

#!/bin/bash

if [ $# -lt 1 ]
then
  me=`basename $0`
  echo "Usage: $me [OSX Application]"
  exit
fi

myPath=/Applications:/Applications/Utilities:/Developer/Applications:$PATH
myPath=\"`echo $myPath | sed 's/:/" "/g'`\"

# Check our custom path and execute the first match
for thisPath in $myPath
do
  thisPath="`echo $thisPath | sed 's/\"//g'`"
  app=$thisPath/$1.app/Contents/MacOS/$1

  if [ -x "$app" ]
  then
    # We found it!
    shift
    sudo -b "$app" $*
    exit
  fi
done

# We didn't find anything.
echo 'Sorry, application not found.'

I saved that file to /usr/local/bin/sopen (using nano ) and then gave it execute permission using chmod.

chmod -x /usr/local/bin/sopen

I could have also granted the execute permission from Finder but I was in a terminal anyway.  Now, although I still need to drop to a terminal in order to edit my system files, all I need to type is

sopen TextEdit /etc/hosts

My script will look for the specified program in /Applications, /Applications/Utilities, /Developer/Applications and then continue on down the regular $PATH.   It’ll execute the first correctly-named program it finds and will pass to it any extra parameters that I specify on the command line.  So the above example will correctly sudo /Applications/TextEdit and will pass it /etc/hosts.

This is just a very simple script and it could be expanded on to perhaps work a bit more like open and use LaunchServices to find a default program to open a certain file type but I’m happy with the way it is.  Maybe others will find it useful too.  Perhaps when I get time I’ll write a Finder plugin to let me elevate from a popup menu and then I can do away with the console completely.

I was left in a position where I could no longer sudo to rename it back.  I had no luck from Finder either and I couldn’t open new Terminal sessions.  I decided to reboot in safe mode by holding down shift while rebooting to see if I could repair the damage from there but my system just wouldn’t come up – I was left staring at the Apple logo.

In case you should ever find yourself in this position, don’t panic too much – After much panicking myself, I managed to fix it by doing the following.  Bear in mind at the time of writing I use Leopard so things may be a little different in future OS X versions.

• Locate your OS X installation disk 1 and pop it in the DVD drive.
• Reboot while holding the C key down to force your Mac to boot from the DVD drive.
• It’ll load up and ask you what language you’d like to use.  Pick one (preferably one you can understand lol).
• The next screen is all about reinstalling.  That’s a last resort really because we can fix things from here.  On the Utilities menu you should see Terminal.  Choose it and the Terminal will open with a bash shell.
• Bear in mind that you’ve not booted from your hard disk so the directory structure will look different to what you’re used to.  Change directory in to /Volumes and then in to your hard disk, possibly called “Macintosh HD” unless you’ve changed it.
• Now you’re actually looking at your hard disk and should be able to change directory in to usr/lib and mv the file back to it’s original name.  Just to clarify, you should not be in /usr/lib.  You should be in /Volumes/Macintosh HD/usr/lib.

Good luck!