I have done some testing of my own, and this does not work. I have also heard it does not work from people in Apple. I suggest removing the story, or at the very least putting a big warning at the top that it is not accurate. I started using this trick in my own code, only to find it was introducing subtle bugs.

Drew

I definitely share your discomfort with passing in a BOOL that way. It is certainly not very pretty.

As for this post, I have been mulling over it for quite a while now. When I wrote it, I was 100% certain that it worked. However, since posting it, I have received several code samples and comments showing me that it does not in fact work.

I have been wrapped up with other projects and have not had a chance to give it the attention it is due. I suspect that I will be posting a retraction of this article in the near future.

-(void) makeTargetFieldFirstResponder:(BOOL) becomeFirstResponder

If I call it like this it fails to pass the becomeFirstResponder argument:

[self performSelector:@selector(makeTargetFieldFirstResponder:) withObject:[NSNumber numberWithBool:YES] afterDelay:duration];

However, if I do this it works fine:

[self performSelector:@selector(makeTargetFieldFirstResponder:) withObject:(id)YES afterDelay:duration];

I must say I’m not really comfortable with this, it seems like taking advantage of a fluke of the language implementation rather than being correct. It’s a shame the Apple documentation is so sparse in this area.

Here’s the program:

import

/* compile with gcc -g -Wall -framework Foundation -o autounbox autounbox.m */

@interface Receiver : NSObject

• (void) printGroovyness: (int)groovy;

@end // Receiver

@implementation Receiver

• (void) printGroovyness: (int)groovy { NSLog (@”Groovy received: %x”, groovy); } // printGroovyness

@end // Receiver

@interface Sender : NSObject @end // Sender

@implementation Sender

• (void) boxingDay: (Receiver *)receiver { [[NSAutoreleasePool alloc] init];

  int value = random() % 300; NSNumber *number = [NSNumber numberWithInt: value];

  NSLog(@”main-threading groovy of %d with pointer %p”, value, number);

  [receiver performSelectorOnMainThread: @selector(printGroovyness:) withObject: number waitUntilDone: NO];

  sleep(10);

} // boxingDay

@end // Sender

int main (int argc, const char *argv[]) { [[NSAutoreleasePool alloc] init];

Sender *sender = [[Sender alloc] init];
Receiver *receiver = [[Receiver alloc] init];

[NSThread detachNewThreadSelector: @selector(boxingDay:)
          toTarget: sender
          withObject: receiver];

// Give the runloop marklar a chance to catch its breath
sleep (1);
[[NSRunLoop mainRunLoop] run];

return (0);

} // main

and the output:

2008-03-14 17:58:07.068 autounbox[2288:1003] main-threading groovy of 283 with pointer 0x20a720 2008-03-14 17:58:08.069 autounbox[2288:807] Groovy received: 20a720

I’d love to know what I’m doing wrong, since this would simplify a primitive-type-passing situation I’m in.

Thanks! ++md

–is progressIndicator != nil? –what happens when you call it directly without performSelectorOnMainThread? You can probably call this from the background thread to test without the world coming to an end.

That would be my suggestion because the auto-unboxing discussed above definitely works. I use it all over the place in iWeb Buddy.

[progressIndicator performSelectorOnMainThread:@selector(incrementBy:) withObject:[NSNumber numberWithDouble:someDouble] waitUntilDone:YES]; // or waitUntilDone:NO, neither work for me

Can you post what you are doing or send me an email with the lines of code you are working with?

mzarra at mac dot com

I have my own NCCommon.h that I can’t live without. While we don’t have automatic boxing, very short convenience method at least makes the code palatable. Behold:

extern NSString* s(const char *str);

define sf(format, …) ([NSString stringWithFormat: format, ##VA_ARGS])

extern NSArray *ary(id item, …); extern NSDictionary *dict(id key, id value, …); extern NSNumber *num(double n);

and NCCommon.m: NSString* s(const char *str) { return [NSString stringWithUTF8String:str]; } NSArray *ary(id item, …) { if(!item) return [NSMutableArray array]; NSMutableArray *ar = [NSMutableArray arrayWithObject:item];

va_list va;
va_start(va, item);
id obj = va_arg(va, id);
while(obj != nil) {
    [ar addObject:obj];
    obj = va_arg(va, id);
}
va_end(va);
return ar;

}

NSDictionary *dict(id key, id value, …) { if(!key) return [NSMutableDictionary dictionary]; NSMutableDictionary *mdict = [NSMutableDictionary dictionaryWithObject:value forKey:key];

va_list va;
va_start(va, value);
id nextkey = va_arg(va, id);
id val = va_arg(va, id);
while(nextkey != nil && val != nil) {
    [mdict setObject:val forKey:nextkey];
    nextkey = va_arg(va, id);
    val = va_arg(va, id);
}
va_end(va);
return mdict;

}

NSNumber *num(double n) { return [NSNumber numberWithDouble:n]; }

(yes, s and num could very well be defines as well… I blame it on being old code.)