Every iOS/Mac OS developer should know this. If you don’t, read it at least 2 times!
This is something any experienced Cocoa developer has been asked at least half a dozen times:
“What’s the best way to learn Objective-C/Cocoa?”
I have two answers to this question:
- Be curious
- Don’t be satisfied
He goes on to finish with the following epithet:
- Know what a pointer is.
- Memorize the memory management rules.
- Never invoke
-retainCount.The second item there is the one I most frequently hear is ‘really difficult’ to understand. It’s not. It’s really not. It looks like this:
- Only the owner of an object needs to think about its memory management.
- You only own an object if you get it from a method whose name begins with any one of:
alloc, including+allocWithZone:new, including+newSomethingSomethinginit, including-initWithSomeParameter(er, no, it doesn’t. I’m being stupid. Sorry.)copy, including-copyWithZone:or-mutableCopyor-mutableCopyWithZone:- If the object doesn’t come from a method matching those rules, you don’t own it.
Edit: Specifically, the method must either be one of the above words, or begin with one followed by an uppercase letter. This means that
+newSomethingreturns an owned reference, but+newestSomethingdoes not. Thanks to Dave DeLong for reminding me of this via email.It’s that simple. If you call something including
alloc,new,init, orcopy, then you must use-release(or-autorelease) to balance that call. If you don’t call one of those methods, you Just Don’t Care.How about CoreFoundation? That’s even simpler: you own an object if it comes from a method containing
Create. The same thing could be said aboutCopy, but CF’s copy constructors are always careful to frequently already containCreate, so we don’t need to. Anything named usingGetreturns an already-managed reference, so you don’t need aCFReleasefor it.Edit: I’m reminded by Peter Hosey that many CF-style APIs outside of CoreFoundation itself tend to use
CopywithoutCreate, for instance those in CoreGraphics. Note however that not everything that looks like a CF object really is one— many are just C wrappers around Carbon-era C++ code.See? Easy. A list of four keywords in Objective-C code indicate the only times you need to ever think about memory management. And one keyword in CoreFoundation to tell you the same.
Now, there are exceptions— usually when something missed the boat, or when an existing API needed to be changed to fix an internal memory-management issue. The documentation will tell you about these very rare cases, but the best way to catch them for now is judicious use of Build & Analyze. The Clang compiler’s static analysis tool knows all about these rules, and can be told about any differences to them by any API. It will tell you explicitly if you’ve released something you don’t own, or have failed to release something you do own. Use it. Love it.
Memory management in Cocoa isn’t difficult. There are rules, but they’re simple and easy to remember. The main thing to remember is:
Don’t over-think it
(via quatermain)
How to make a Scrolling Text View on Mac OS X
This post will show how to put together a horizontal scrolling Text View using Cocoa. This is a simple task that doesn’t require advanced Objective C and Cocoa knowledge.
Introduction
If you’ve tried to display information on the Mac OS X status bar then you know that space is limited and the available width changes based on the user’s installed apps.
A lot of applications show only an icon, that will become highlighted to notify the user when something happens, waiting then for a click or mouse hover to display a menu (some applications even have customized panels, usually mimicking Growl notifications).
There is (at least) one application that comes with Mac OS X that does a nice and simple work-around to this problem, scrolling text horizontally for the user, the VPN Status Notifier. When you connect it, it wides itself and then scrolls the states right to left until it establishes a connection.
A month ago I was looking for a way to do the same, I never liked those “Growl style” panels and I needed to show more than one simple icon, so scrolling text seemed to be the best idea. Unfortunately I couldn’t find a way to do this with NSTextField (I’m sure it can be made though, I was just lazy) so I made myself a custom NSView to solve this.
This is a very simple thing to make if you’ve been learning Cocoa for more than two weeks, nonetheless I decided to post it because I couldn’t find a “download, plug and play” ScrollingTextView online, and feel that there are people like me searching for it.
So Where Is The Download Button?
You can find FBScrollingTextView on Github. If you find something wrong with it and you would like to fix it just open an issue or a pull request.
To the Code
@interface FBScrollingTextView : NSView {
NSString *string;
CGFloat scrollingSpeed;
NSFont *font;
@private
CGFloat refreshRate;
NSTimer *tickTockStartScrolling;
NSTimer *tickTockScroll;
NSPoint cursor;
}
@property (readwrite, retain, nonatomic) NSFont *font;
@property (readwrite) CGFloat scrollingSpeed;
@property (readwrite, retain, nonatomic) NSString *string;
@end
As I stated before, FBScrollingTextView is a NSView and most of it’s variables are self explanatory. The default scrollingSpeed is 2, and I would recommend a value between 1 and 10.
The timer tickTockStartScrolling is just to introduce delay and tickTockScroll does the trick.
For example: when you set a string you wouldn’t want it to start scrolling right away as (depending on your scrollingSpeed) the user will not be able to read the first letter. tickTockStartScrolling starts tickTockScroll after a specific time (kFBScrollingTextViewStartScrollingDelay) so we have readable information.
- (void)scrollText {
cursor.x-=1;
[self setNeedsDisplay:YES];
}
- (void)startScrolling {
if (!tickTockScroll) {
tickTockScroll =
[NSTimer scheduledTimerWithTimeInterval:refreshRate/scrollingSpeed
target:self
selector:@selector(scrollText)
userInfo:nil repeats:YES];
}
[tickTockStartScrolling release];
tickTockStartScrolling = nil;
}
- (CGFloat)stringWidth {
if (!string) return 0;
NSSize stringSize = [string sizeWithAttributes:
[NSDictionary dictionaryWithObjectsAndKeys:font,NSFontAttributeName,nil]];
return stringSize.width;
}
-[FBScrollingTextView scrollText] is the method where we do the “scrolling”, it just decrements a cursor and calls setNeedsDisplay.
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
// Drawing code.
CGFloat sWidth = round([self stringWidth]);
CGFloat rWidth = round(rect.size.width);
CGFloat spacing = round(rWidth*kFBScrollingTextViewSpacing);
if ((cursor.x*-1) == sWidth) {
CGFloat diff = spacing - (sWidth+cursor.x);
cursor.x = rWidth-diff;
}
NSDictionary *attrs =
[NSDictionary dictionaryWithObjectsAndKeys:font, NSFontAttributeName,nil];
[string drawAtPoint:cursor withAttributes:attrs];
CGFloat diff = spacing - (sWidth+cursor.x);
if (diff >= 0) {
NSPoint point = NSMakePoint(rWidth-diff, cursor.y);
[string drawAtPoint:point withAttributes:attrs];
}
}
As you can see drawRect is where we do the magic, making some calculations to get to the point where the beginning of the string is supposed to be and then calling -[NSString drawAtPoint:withAttributes:] with that point.
Conclusion
The aim of this post was to show a very simple View that you can add to a NSStatusItem and just scroll the entire bible if you’re inclined.
Tweet me if you make something cool with it.
Hello World!
Two years ago I started developing my first iPhone application. Has I made my first steps into Cocoa and Objective C, reading Hillegass’s Cocoa Programming for Mac OS X , I was amazed not only with the book, which I highly recommend to beginners, but also with Cocoa. But after a while I was on my own and quickly realized that you can easily find help online about any easy task but if you’re trying to, for example, make a grid view on iOS you would need to search deeper (in this case I ended up using Jim Dovey’s AQGridView, you can find it forked at my Github).
The point is that I’ve spent days, or even weeks, developing a specific feature or task. And every time I solve a problem I couldn’t find how to online I think: “What if I had a blog and published a small tutorial on how to solve this?”. You’re reading that blog.
Now, English is not my native language, so please be constructive if you’re commenting just to tell me that I wrote something wrong.
If you wish yo contact me, check the About Me page.
Hello World!
