Append to beginning of NSString method - ios

Question

I would like to append NSString A in front of NSString B. Is there a built in method to append to the beginning of a NSString instead of the end of the NSString?
I know that I can use stringWithFormat, but then what is the difference between using stringWithFormat and stringByAppendingString to add text to the end of a NSString?

Answer 1

If you can append to the end of a string, you can prepend to the beginning of the string.
Append
NSString* a = #"A";
NSString* b = #"B";
NSString* result = [a stringByAppendingString:b]; // Prints "AB"
Prepend
NSString* a = #"A";
NSString* b = #"B";
NSString* result = [b stringByAppendingString:a]; // Prints "BA"

Answer 2

Single line solution:
myString = [#"pretext" stringByAppendingString:myString];

Answer 3

You can use stringWithFormat too:
NSString *A = #"ThisIsStringA";
NSString *B = #"ThisIsStringB";
B = [NSString stringWithFormat:#"%#%#",A,B];
stringByAppendingString is an instance method of NSString,
stringWithFormat is a class method of the class NSString.

Answer 4

It's probably worth pointing out that there is no such thing as "appending one string onto another". NSString is immutable.
In every case, you are "creating a new string that consists of one string following another".
It doesn't matter that you put the newly created string back into the same variable.
You are never "adding text to the end of a string".

Answer 5

Here I’ve solution in Swift:
extension String {
// Add prefix only, if there is not such prefix into a string
mutating func addPrefixIfNeeded(_ prefixString: String?) {
guard let stringValue = prefixString, !self.hasPrefix(stringValue) else {
return
}
self = stringValue + self
}
// Add force full prefix, whether there is already such prefix into a string
mutating func addPrefix(_ prefixString: String?) {
guard let stringValue = prefixString else {
return
}
self = stringValue + self
}
}