Volume Number: 15 (1999)
Issue Number: 7
Column Tag: Tips & Tidbits

July 99 Tips

by Jeff Clites, online@mactech.com

Many apps have a need to open an URL in OmniWeb, or a compose window in MailViewer, and this is relatively easy since both applications offer a Service for this. However, in order to have this service reliably performed, it is best to delay the invocation until the next event loop. This can be done rather easily. When your app needs to open an URL (in this case a static one, but you could just as easily pass in a value), call [openUrl:self]. This will cause performOpenUrl: to be scheduled to run after a minimum delay of 0.0. In reality though, it will be executed the next time through the event loop.

When you are using a Macintosh but have to read a file created on a computer with an Intel processor, or when you have to write a file for later use on an Intel machine, this difference is something you have to worry about. You can use the following routines to convert shorts and longs back and forth between the two byte orders.

- openUrl:sender;
{
	NSString *urlString = "http://www.stepwise.com/";
	[self performSelector: @selector(performOpenUrl:) 
			withObject: urlString afterDelay: 0.0];
	return self;
}

- performOpenUrl:(NSString *)urlName;
{
	NSPasteboard	*pboard;
	NSArray			*urlPboardTypes;
	NSString		*serviceName;

	pboard = [NSPasteboard 
			pasteboardWithName:@"URLServicePasteboard"];
	urlPboardTypes = [NSArray 
			arrayWithObjects:NSStringPboardType, nil];
	[pboard declareTypes:urlPboardTypes owner:nil];
	[pboard setString:urlName forType:NSStringPboardType];

	if((serviceName = [[NSUserDefaults standardUserDefaults] 
			stringForKey:@"URLService"]) == nil)
		serviceName = @"OmniWeb/Open URL";
	NSPerformService(serviceName, pboard);
	return self;
}

You'll notice above that we first attempt to read URLService from the defaults database; this would allow us to change the default browser in our preferences. You can cause MailViewer to open an empty compose window using a similar technique, substituting @selector(mailto:) for @selector(performOpenUrl:) in the above call to performSelector:withObject:afterDelay:

- mailto:sender;
{
	NSPasteboard	*pboard;
	NSArray		*urlPboardTypes;
	NSString	*serviceName = @"MailViewer/Mail To";

	pboard = [NSPasteboard 
			pasteboardWithName:@"MailViewerServicePasteboard"];
	urlPboardTypes = [NSArray 
			arrayWithObjects:NSStringPboardType, nil];
	[pboard declareTypes:urlPboardTypes owner:nil];
	[pboard setString:[sender title] 
			forType:NSStringPboardType];
	NSPerformService(serviceName, pboard);
	return self;
}

Scott Anguish
sanguish@digifix.com

Conversion from Intel Byte Order, Again

Last month we presented a pair of routines for converting integers between the two different byte orderings expected by Motorola and Intel processors. That code should work under any architecture, but if you are on a Mac there is a much more efficient way to implement this using the byte reversing instructions built into every PowerPC processor:

inline unsigned long IntelToMotorolaLong (unsigned long *original)
{
	return (__lwbrx(original, 0));
}

inline unsigned short IntelToMotorolaShort (unsigned short *original)
{
	return (__lhbrx(original, 0));
}

Eric Lengyel
lengyel@apple.com