it is the question from my friends. I have research some code from the internet but no help, i think it should working, the question is right.
NNString *s = [[NNString alloc]initWithString:#"hello"];
[s appendString:#"there"];
NSString is immutable, you'd need to use an instance of NSMutableString in order to be able to append to it.
NSMutableString *s = [[NSMutableString alloc] initWithString:#"hello"];
[s appendString:#"there"];
Alternatively you could replace the instance using stringByApendingString:.
Try this if you want to keep the string immutable:
s = [s stringByAppendingString:#" there"];
Related
Let's say I have string like this:
NSString *myString = [NSString stringWithFormat:#"%#%#%#%#%#",variable1,variable2,variable3,variable4,variable5];
and if variable2 is nil I don't want that in my string, like this:
NSString *myString = [NSString stringWithFormat:#"%#%#%#%#",variable1,variable3,variable4,variable5];
Question
Is there any way to do this without having a lot of if-statements?
Don't use [NSString stringWithFormat:], and instead create an NSMutableString and append strings as necessary:
NSMutableString *s = [[NSMutableString alloc] init];
if (variable1)
[s appendString:variable1];
if (variable2)
[s appendString:variable2];
if (variable3)
[s appendString:variable3];
if (variable4)
[s appendString:variable4];
if (variable5)
[s appendString:variable5];
(sorry I missed your point about "not having lots of if statements", however I don't think it can be avoided).
The easiest way is to use the compacted ternary operator to replace a null with an empty string. Using a slightly abridged version of your example:
NSString *myString = [NSString stringWithFormat:#"%#%#",variable1 ?: #"",variable2 ?: #""];
This question already has answers here:
Convert NSArray to NSString in Objective-C
(9 answers)
Closed 9 years ago.
I wish to know how to convert an NSArray (for example: ) into an Objective-C string (NSString).
Also, how do I concatenate two strings together? So, in PHP it's:
$variable1 = "string one":
$variable2 = $variable1;
But I need it in Objective-C
Possible duplication: Convert NSArray to NSString in Objective-C
Firstly, that is not PHP concatenation, This is:
$variable1 = "Hello":
$variable1 .= "World";
see: https://stackoverflow.com/a/11441389/1255945
Next, Stackoverflow isnt a personal tutor. You should only post here specific problems and provide as much code and information as you can, not just stuff thats basically saying "I cant be bothered to look myself, tell me".
I must admit I have done this myself so i'm not having a go at you, just trying to be polite as share my knowledge and experience
With that in mind, to convert an NSArray to NSString
Taken from: http://ios-blog.co.uk/tutorials/objective-c-strings-a-guide-for-beginners/
NSString * resultString = [[array valueForKey:#"description"] componentsJoinedByString:#""];
If you want to split the string into an array use a method called componentsSeparatedByString to achieve this:
NSString *yourString = #"This is a test string";
NSArray *yourWords = [myString componentsSeparatedByString:#" "];
// yourWords is now: [#"This", #"is", #"a", #"test", #"string"]
if you need to split on a set of several different characters, use NSString’s componentsSeparatedByCharactersInSet:
NSString *yourString = #"Foo-bar/iOS-Blog";
NSArray *yourWords = [myString componentsSeparatedByCharactersInSet:
[NSCharacterSet characterSetWithCharactersInString:#"-/"]
];
// yourWords is now: [#"Foo", #"bar", #"iOS", #"Blog"]
Note however that the separator string can’t be blank. If you need to separate a string into its individual characters, just loop through the length of the string and convert each char into a new string:
NSMutableArray *characters = [[NSMutableArray alloc] initWithCapacity:[myString length]];
for (int i=0; i < [myString length]; i++) {
NSString *ichar = [NSString stringWithFormat:#"%c", [myString characterAtIndex:i]];
[characters addObject:ichar];
}
Hope this helps, and Good luck developing :)
When I make:
NSString x = #"test"
How do I edit it so that it becomes "testing"?
And when I put:
NSMutableString x = [[NSMutableString alloc] initWithString:#"test"];
There is an error that says:
Initializer element is not a compile-time constant.
Thanks
When declaring NSMutableString, you missed the asterisk:
NSMutableString *x = [[NSMutableString alloc] initWithString:#"test"];
// Here --------^
With a mutable string in hand, you can do
[x appendString:#"ing"];
to make x equal testing.
You do not have to go through a mutable string - this will also work:
NSString *testing = [NSString stringWithFormat:#"%#ing", test];
You need to declare your NSString or NSMutableString as *x. These are pointers to objects.
To change a string in code is quite easy, for example:
NSString *test = #"Test";
test = [test stringByAppendingString:#"ing"];
And the value in test will now be Testing.
There are a lot of great NSString methods, both instance and class methods, for manipulating and working with strings. Check the documentation for the complete list!
if you want to add multiple or single strings to an existing NSString use the following
NSString *x = [NSString stringWithFormat:#"%#%#", #"test",#"ing"];
How to change value of mutable string ? Here is what I do
NSString *str = #"This is string";
NSMutableString *str = [NSMutableString stringWithFormat:#"%#", str];
str = #"New string" -> wrong incompatible pointer types assigning to NSMutableString from NSString
You only need to use NSMutableString if you want to change parts of the string in place (append, insert etc.), often for performance reasons.
If you want to assign new values to the string variable, you're fine with a good old NSString as your last line simple assigns a complete new string object to str:
You can use setString to replace the whole string:
NSString *str = #"This is string";
NSMutableString *mutableStr = [NSMutableString stringWithFormat:#"%#", str];
...
[mutableStr setString:#"a different non mutable string"];
As indicated in another answer, a non-mutable NSString may be enough for your purposes.
This is how you should initialize a NSMutableString:
NSMutableString *string = [[NSMutableString alloc]init];
You could use any other way specified in the docs. The way you are doing it, you are not creating any instance of the NSMutableString class. Then, if you want to add some string to it:
[string appendString:#"content"];
I have an NSMutableString called makeString. I want to create it at the beginning of my program without having to set its text. I then want to be able to set its text. I am currently using the following to create it.
NSMutableString *make2String = [[NSMutableString alloc] initWithString:#""];
I am then using the following to set its text value.
make2String = [NSString stringWithFormat:#"Gold.png"];
Is this ok to do or is there a better way to set an NSMutableString's text?
That is not ok, you are replacing your mutable string with an ordinary immutable string (and leaking the original mutable string in the process). You could do [NSMutableString stringWithFormat:#"Gold.png"] after releasing the old string if you wanted to go that route. Or you could use NSMutableString's setString: method to set the content.
But if you're not actually mutating the string and just assigning different strings, you don't need NSMutableString at all. Just do make2String = #"Gold.png"; and be done with it.
NSMutableString * aString = [NSMutableString alloc];
aString = [aString init];
[aString setString:#"yourText"];
[aString setString:#"yourNewText"];
[aString setString:#"yourNewNewText"];
//...
[aString release];
make2String = [NSMutableString stringWithFormat:#"Gold.png"];
FYI: This is how I allocate NSMutableStrings without setting text
NSMutableString *string = [[NSMutableString alloc] init];