I'm starting to develop for the iPhone. I have a beginner-type question, I'm sure:
I have this, which works:
testLabel.text = [NSString stringWithFormat:@"%@ to %@", testLabel.text, newLabelText];
I wish I could use the "+=" operator, but I get a compile error (Invalid operands to binary +, have 'struct NSString *' and 'struct NSString *'):
testLabel.text += [NSString stringWithFormat:@"to %@", newLabelText];
Why can't I do this?
Also, how can I shorten my first snippet of code?
Think about using an NSMutableString - you can use the appendString: method, as in:
NSMutableString *str = [@"hello" mutableCopy];
[str appendString:@" world!"];
You can't use the += operator because C and Objective-C do not allow operator overloading. You're trying to use += with two pointer types, which is not allowed -- if the left-hand side of a += expression has a pointer type, then the right-hand side must be of an integral type, and the result is pointer arithmetic, which is not what you want in this case.
That can't be done because ObjectiveC does not support it, ObjectiveC is a small layer over C.
testLabel.text = [testLabel.text stringByAppendingFormat:@" to %@", newLabelText];
NSString are NOT mutable (they can't be changed), that's why you can't use +=.
NSMutableString can be changed. You might be able to use them here.
Your code is already pretty minimal. Objective-C is a expressive language so just get used to long, descriptive function and variable names.
try this:
// usage: label.text += "abc"
public func += (a:inout String?, b:String) {
a = (a ?? "") + b
}
give this custom operator a try:
let label = UILabel()
label.text = "abc"
label.text += "_def"
print(label.text) // “abc_def”
