Cocoa Dev

Macro Goodness

w.berberich@salient.de — 2007-11-17T18:25:53+01:00

If you read books on programming they all tell you to write documented code. But even better is to write compact code. Code that is so compact, it can even document itself. Objective-C is already pretty self documenting but some common conventions require you to write the same kind of code ever and ever again, just to follow these conventions. Macros have been ever very helpful in these cases. Following some examples. You can imagine how many macros like this I use in my code.

Objective C 2.0 will make the whole retain release cycle go away but I am still sticked to Tiger.


+ (void)setSomeReference:(NSObject *)object
{
    BEReferenceWithRetain(_myStrongReference, object);
}

Uses this macro. I have others for BEReferenceWithCopy, BERelease and more.


#define BEReferenceWithRetain(a, b) \
{ \
    id bb = b; \
    if (a != bb) \
    { \
        if (bb != nil) \
            [bb retain]; \
        [a release]; \
        a = bb; \
    } \
}

Another common task is adding elements to a result set or array. If nothing should be added the method might return nil, but otherwise the resultArray. So this code is a very common task:


NSMutableArray *resultArray = nil;

while (someLoop)
{
    if (shouldNotAdd)
        continue;

    BEAddObjectToMutableArray(resultArray, newItem);
}

It uses this macro


#define BEAddObjectToMutableArray(array, item) \
{ \
    if (item) { \
        if (array == NULL) {\
            array = [NSMutableArray arrayWithObject:item]; \
        } else {\
            [array addObject:item]; \
        }\
    }\
}

[NSURLConnection sendSynchronousRequest:returningResponse:error:]

w.berberich@salient.de — 2007-11-17T18:23:28+01:00

I had a lot of trouble with this beast in Tiger and it came up in Leopard again. As I did not find any solutions elsewhere, here's how I fixed it for me.

Problem: NSURLConnection sendSynchronousRequest:returningResponse:error starts a download and blocks the calling thread until all bytes are received from the stream. In most cases this just works. But for some reason, if you call this on the main thread, it sometimes does not unlock the thread resulting in an application hang.
Lesson Learned: Fully synchronous url requests are impossible. Always load networks resources from a background thread.

Next problem: Code Data loads an XML data store using this method. So it's no wonder that sometimes, when the arraycontroller gets filled, your application just hangs. Or, under Tiger, crashes because the NSData the store loads the XML into gets deallocated before the store is even finished loading.

Solution: To fix this, I wrote a category for NSXMLDocument that loads file resources using standard file methods. Otherwise it does what I expect it to do in the default implementation.


- (id)initWithContentsOfURL:(NSURL *)url options:(unsigned int)mask error:(NSError **)error
{
    id result = nil;
    NSData *data = nil;
    if ([url isFileURL])
    {
        data = [[NSData alloc] initWithContentsOfFile:[url path]];
    }
    else
    {
        NSHTTPURLResponse *response = NULL;
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadIgnoringCacheData timeoutInterval:10];
        data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:error];
    }
    result = [self initWithData:data options:mask error:error];
    return result;
}

Removing Leopard Marketing Features

w.berberich@salient.de — 2007-11-17T17:34:01+01:00

Not all of us like the new Leopard look although it's a great product. Here are some ways to make Leopard look more familiar to previous versions of Mac OS X. All tips require you to use the shell.

Remove the translucent Menu Bar effect

sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 0.62

Switch the dock to 2D mode

defaults write com.apple.dock no-glass -boolean YES

Remove the default space desktop image

Even though you might have set another desktop background, the Login window still shows the space theme. To login look more neutral move the Image away.
sudo mv /System/Library/CoreServices/DefaultDesktop.jpg /System/Library/CoreServices/xDefaultDesktop.jpg