int myInt；
NSNumber *myNumber = [NSNumber numberWithInt:myInt];
int myInt = [myNumber intValue];；
1. NSArray/NSMutableArray cannot hold ints or NSInteger
>> although NSInteger is notationally similar to NSNumber, NSNumber is an object whileNSInteger is an alias for int or long (depending on whether you’re running a 32/64 bits architecture). NSArray can only hold objects. If you want to add a number to an NSArray, useNSNumber and initialise your number with something like [NSNumber numberWithInt:26].
(Yes, you can use standard C arrays, there are quite a few posts about this around)
2. NSNumber doesn’t auto-unbox
>> If you try to assign NSNumber to an int (or, better, an NSInteger), you’re assigning a pointer, not the actual number. To get the actual number, use something like: [MyNSNumber integerValue]
3. Strings don’t concatenate with [+] or [.]
>> If something like “Score: “+score is what you’re used to, try making friends with:
[NSString stringWithFormat:@"Score: %i", score];
4. In, (void)applicationDidFinishLaunching:(UIApplication *)application {…}not all IBOutlets depending on your nib file will initialize until your view is added to the main window
after [window makeKeyAndVisible]; it should be safe to access all IBOutlets attached to yourviewController.
5. I updated the frame property of a subview, but the coordinates look incorrect.
>> after updating the UIView.frame property on a subview, invoke setNeedsLayout on the parent view.
6. NSTimer fires at the wrong time / fires too many times
>> When you allocate/init NSTimer with the usual code, you don’t need to invoke fire(). NSTimer is setup as soon as it’s initialized and fire() shouldn’t be called directly as it, *doh!* fires the timer.
>> Whatever you name your callback method, it should take a unique NSTimer argument ( the selector argument would typically look like @selector(myCallback:) with the semi-colon at the end).
What happened to me is that my timer kept firing over and over even though repeat:NO was set. Adding the timer argument to the callback fixed the problem.
from：
@“oogtech.org/content/category/iphoneitouch-programming/”
