guys i m getting this basic error "initializer element is not constant"..not able to figure where exactly i failed .below is the code.`
#implementation myfirstflickrappViewController
NSString *const FlickrAPIKey = #"14c39d71001b0fb84d1dacb6049580ec";
NSString *const text = #"hello";
NSString *urlString =
[NSString stringWithFormat:
#"http://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=%#&tags=%#&per_page=25&format=json&nojsoncallback=1",
FlickrAPIKey, text];
You call a method on NSString (stringWithFormat:) in a place where you are not allowed to do so - namely outside of a method or function. Only constant expressions like string literals are allowed there.
You might put that code in your -init method or the class initializer.
Related
I want to get the class name of an object as what we are using.
That means now if I write this code
NSString *s = [NSString string];
NSLog(#"%#",[s class]);
The output is __NSCFConstantString
How can I get it as NSString itself ?
Note : NSString is just an example
I know __NSCFConstantString is correct. But my intention is to get like NSString. Is there any way to acheive this?
Give these a try, they'll output NSString. Keep in mind, the second set requires importing the Objective-C runtime header.
#import <objc/runtime.h>
NSString *string = #"I'm a string.";
NSLog(#"%#",NSStringFromClass([string classForCoder]));
NSLog(#"%#",NSStringFromClass([string classForKeyedArchiver]));
NSLog(#"%s",class_getName([string classForCoder]));
NSLog(#"%s",class_getName([string classForKeyedArchiver]));
Now, this won't work in all cases. For example, trying to get the class of NSConstantString, in this manner will output NSString. If you require checking the class name as a string in this way, you probably should reconsider your approach to solving the problem.
NSString is a so-called "class cluster". That means that the init methods will return
an instance of some subclass (such as __NSCFConstantString or __NSCFString).
You will never get an instance with the class equal to NSString.
If your intention is to check whether an object is a NSString or not then
use isKindOfClass:
if ([s isKindOfClass:[NSString class]]) {
// this is a string …
}
Other examples of class clusters are NSNumber, NSDictionary, NSArray
and their mutable variants.
NSLog(#"%#", NSStringFromClass([s class]));
I’m currently trying to learn Objective-C by reading books and online tutorials, also referring to the Apple documentation but some things just don’t click. I have a question about classes, I have been using the NSString for a while now without putting too much attention on how it is used.
I was under the impression that in order for someone to be able to use a method from a certain class in Objective-C you first needed to instantiate it, something like…
ClasssName *varName = [[ClassName alloc]init];
Then you would call methods like...
[varName someMethod];
But looking at how the NSString is used I’m now I little confused, for instance here is how we would normally use it...
NSString *someString = #"some text here";
[someString stringByAppendingFormat: #"some text = %d", 3];
Following what I have read about classes we would need to do something like the following instead.
NSString *someString = [[NSString alloc]initWithString: #"some text here"];
[someString stringByAppendingFormat: #"some text = %d", 3];
Can someone explain why some classes do not require instantiation before using its methods?
Objective-C knows some abbreviations that are called literals. The compiler is aware of the special notation. A string literal is compiled into the binary and exits throughout the lifetime of an app.
For most cases it will behave like an object created on runtime.
if two literals are identical, only one object will be created and live forever
if you create NSString *string = [[NSString alloc] initWithString:#"My String"]; with #"My String" being used as a literal before, also string can point to it.
Since Apple LLVM Compiler 4.0 Objective-C knows some more literals. But in contrast to string literals these literals are created during runtime through convenient initializers.
Note that
[someString stringByAppendingFormat: #"some text = %d", 3];
does not change someString. It returns a new string object.
NSString *newString = [someString stringByAppendingFormat: #"some text = %d", 3];
The #"Text" syntax gives you an autoreleased string back, it can be thought of as a shorthand.
when you write
[[NSString alloc]initWithString: #”some text here”];
you conceptually create an autoreleased string with #”some text here” and then you create a retained new string with initWithString.
I am trying to set the initial text for what the twitter message should say in my app using a NSString from my appDelegate. Check out the code here:
NSString *tweet;
tweet=[MyWebFunction tweet:appDelegate.stadium_id];
if([deviceType hasPrefix:#"5."]){
// Create the view controller
TWTweetComposeViewController *twitter = [[TWTweetComposeViewController alloc] init];
[twitter setInitialText:#"#%",tweet];
The problem is, is there is an error at the twitter setInitialText that there are Too many arguments to method call, expected 1, have 2. ?!?!?
Any help is greatly appreciated. :)
The TWTweetComposeViewController method setInitialText only takes one argument, being of type NSString*. You cannot simply format any and all NSString variables passed to a method as you can with the NSString method stringWithFormat (which is, I imagine, where you've seen the syntax [NSString stringWithFormat:#"%#", myString]).
In your case, you either need to simply call:
[twitter setInitialText:tweet];
or call:
[twitter setInitialText:[NSString stringWithFormat:#"%#", tweet]]
EDIT
I feel it necessary to add, to further your understanding, that a method only takes a variable number of arguments (such as stringWithFormat) when its declaration ends with ...
For example, looking in the docs for NSString reveals that stringWithFormat is declared as such:
+(id) stringWithFormat:(NSString *)format, ...;
Similarly, arrayWithObjects in NSArray is declared as such:
+(id) arrayWithObjects:(id)firstObj, ...;
which one would use like:
NSString* myString1 = #"foo";
NSString* myString2 = #"bar";
NSNumber* myNumber = [NSNumber numberWithInt:42];
NSArray* myArray = [NSArray arrayWithObjects:myString1, myString2, myNumber, nil];
Try [twitter setInitialText:tweet];
If you really need formatted text for a more complex case, try
[twitter setInitialText:[NSString stringWithFormat:#"%#", tweet]];
"[twitter setInitialText:#"#%",tweet];"
you just got your "#" and your "%" the wrong way round it should be
[twitter setInitialText:#"**%#**",tweet];
I'm trying to instanciate a constant NSString by concatanating other NSString instances.
Here is what I'm doing in my implementation file :
static NSString *const MY_CONST = #"TEST";
static NSString *const MY_CONCATENATE_CONST = [NSString stringWithFormat:#"STRING %#", MY_CONST];
It leads to the following compilation error : Initializer element is not constant
I suppose this is because stringWithFormat doesn't return a constant NSString, but since there is no other way to concatenate strings in Obj-C, what am I supposed to do ?
Thanks for your help,
Eric.
I thought there must be a way to do this but the best I could do was using a #define directive. For example,
// Define the base url as an NSString
#define BASE_URL #"http://www.milhouse.co.uk/"
// Now the derived strings glued by magic
NSString *const kBaseURL = BASE_URL;
NSString *const kStatusURL = BASE_URL #"status.html";
NSString *const kBalanceURL = BASE_URL #"balance.html";
static const objects value is determined at compile-time so you indeed cannot add any method calls to their initialization. As an alternative you can do the following:
static NSString *const MY_CONST = #"TEST";
static NSString *MY_CONCATENATE_CONST = nil;
if (nil == MY_CONCATENATE_CONST)
MY_CONCATENATE_CONST = [NSString stringWithFormat:#"STRING %#", MY_CONST];
I think you need to step back and think about if the string needs to be defined as a const.
Clearly the string isn't a constant since you are trying to assign a new value to it - and that is not possible since you specifically instructed the compiler to make sure the value wasn't changed by using the const keyword.
If the string resides as a property in a class you could make it a read-only property - i.e. accessor method but no setter method. You would then be able to construct your string as you wish in the class internally while keeping the callers from changing the value.
I am curious how I might override the description method that is used when you do the following (see below) for an object. I basically want to better format the output, but am unsure about how I might go about setting this up.
NSLog(#"ARRAY: %#", myArray);
many thanks
EDIT_001
Although subclassing NSArray would have worked I instead decided that I would add a category to NSArray (having not used one before) Here is what I added ...
// ------------------------------------------------------------------- **
// CATAGORY: NSArray
// ------------------------------------------------------------------- **
#interface NSArray (displayNSArray)
-(NSString*)display;
#end
#implementation NSArray (displayNSArray)
-(NSString*)display {
id eachIndex;
NSMutableString *outString = [[[NSMutableString alloc] init] autorelease];
[outString appendString:#"("];
for(eachIndex in self) {
[outString appendString:[eachIndex description]];
[outString appendString:#" "];
}
[outString insertString:#")" atIndex:[outString length]-1];
return(outString);
}
#end
gary
If you're doing this a lot, the easiest way to reformat the display of your array would be to add a new prettyPrint category to the NSArray class.
#interface NSArray ( PrettyPrintNSArray )
- (NSSTring *)prettyPrint;
#end
#implementation NSArray ( PrettyPrintNSArray )
- (NSString *)prettyPrint {
NSMutableString *outputString = [[NSMutableString alloc] init];
for( id item in self ) {
[outputString appendString:[item description]];
}
return outputString;
}
#end
Obviously you'd need to alter the for loop to get the formatting the way you want it.
I'm assuming that you myArray variable is an instance of the NSArray/NSMutableArray class.
When NSLog() encounters the # character in its format string, it calls the -description: method on the object. This is a method on the root class, NSObject from which all other Cocoa classes inherit. -description: returns an NSString allowing any object that implements this method to be passed into NSLog(#"#",anyObject) and have a nicely formatted output. The string returned can be anything you care to construct.
For your specific problem, you could subclass NSMutableArray and override the -description: method with your own implementation. Then utilise your subclass instead of NSMutableArray.
For more information on NSObject and -description: see Apple's docs.
From Formatting string objects:
NSString supports the format characters defined for the ANSI C functionprintf(), plus ‘#’ for any object. If the object responds to the descriptionWithLocale: message, NSString sends that message to retrieve the text representation, otherwise, it sends a description message.
So to customize array conversion to string you should change NSArray descriptionWithLocale: implementation. Here's an example of how you can replace object method in run-time.