Is this the standard way to get text from label and concatenate with string in iOS?

Question

Please bear with me as I'm very new to the world of iOS and Objective-C. I've read Apple's Obj-C primer, as well as a few free ones provided on the web.

On a button press, I'm trying to simply take the text of a label and concatenate it with a string. My mindset is still very much in Android/Java and how simple it could be, but I'm having trouble here. Nonetheless here is my code:

- (IBAction)myButton:(UIButton *)sender {
    self.myLabel.text = [self.myLabel.text stringByAppendingString:@"obj-c is hard =/"];

}

It seems pretty standard, but I can imagine myself doing this often so I want to make sure this is correct or what other ways are there to do this?

score 2 · Answer 1 · edited Jun 06 '13 at 09:03

2

Yes this is correct way. And if you want to use another method then use this one

self.myLabel.text = [NSString stringWithFormat:@"%@ obj-c is hard =/",self.myLabel.text];

edited Jun 06 '13 at 09:03

John Topley

113,588
46
195
237

answered Jun 06 '13 at 05:08

Dharmbir Singh

17,485
5
50
66

`stringWithFormat` will allow you to pass multiple arguments? Unlike `stringByAppendingString` correct? – EGHDK Jun 06 '13 at 05:11

score 0 · Answer 2 · edited May 23 '17 at 11:49

It is the standard way to join string.As ios updated syntaxes to make it easy like NSArray and NSDictiornary delaration but for concatenation it has not declared any shortcut way.

Have a look at this

OR

you can use a trick to simplify concatenation of string.Pass a parameter to macro and use following joining literal syntax.

#define STRING(text) @""text""

@implementation SPTViewController

- (void)viewDidLoad
{
    NSString *joinedFromLiterals =STRING(@"Congratulations!, ") @"I " @"really " @"enjoy " @"carpenting!";
    NSLog(@"joined string %@",joinedFromLiterals);

    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

output is ---------

joined string Congratulations!, I really enjoy carpenting!

score 0 · Answer 3 · answered Jun 06 '13 at 09:26

Yes, this is correct, but there is a gotcha. If you haven't previously set the value of self.myLabel.text, it will be nil by default. Then the result of calling any method (like [self.myLabel.text stringByAppendingString:@"obj-c is hard =/"]) will also be nil, so myLabel will still have empty text. The way Objective-C handlesnil values is different than handling null in Java.
So to be safe, initialize label's text first:

self.myLabel.text = @"";

score 0 · Answer 4 · answered Jun 06 '13 at 09:35

You are doing it right. Sure Objective-C is a bit more verbose than C# or Java or even Visual Basic .net (as I used to work on all those languages) but don't be bugged by those long method names. Although some #defines can be very helpful like (rewritten as C inline function):

static inline __attribute__((always_inline))
__attribute__((format(NSStirng, 1, 2)) NSString *SKSTR(NSString *fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    NSString *string = [[NSString alloc] initWithFormat:fmt arguments:args];
    va_end(args);
#if !__has_feature(objc_arc)
    [string autorelease];
#endif
    return string;
}

Hope the __attribute__s and #ifs does not confuse you - you can safely ignore them.

To use:

self.label.text = SKSTR(@"%@, ugh!", self.label.text); // just like NSLog or snprintf :)

Is this the standard way to get text from label and concatenate with string in iOS?

4 Answers4