Normally, if I have an NSArray of just NSString's, I can use the NSArray's method:
- (NSString *)componentsJoinedByString:(NSString *)separator
to get a String (like "John,David,Peter"). However, if I have an NSArray of Core Data Entity objects and I just need to to get 1 attribute within (say, the "name" attribute only of each entity object), what is the easiest way to do this?
The Core Data entity object can have many attributes (name, phone, birthdate), but I just want a string like "John,David,Peter".
The following will do a fetch for only the name properties of the Person objects:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Person"];
request.propertiesToFetch = #[#"name"];
request.resultType = NSDictionaryResultType;
NSArray *array = [managedObjectContext executeFetchRequest:request error:nil];
NSString *names = [[array valueForKey:#"name"] componentsJoinedByString:#","];
NSLog(#"%#", names);
You need to set the resultType to NSDictionaryResultType otherwise it will ignore propertiesToFetch. The result from the fetch is an array of Dictionaries. Using valueForKey and componentsJoinedByString will create a single string out of all the names.
Your best option is the straightforward one of building up a NSMutableString by iterating over the items in you array and asking each one for its name to use in appendString:. You could add a description method to the entity object and then use the method you mentioned but description is used for other things and would probably cause conflicts.
// Assuming you have the list of entities - NSArray *entityObjects
NSMutableString *nameAttributes = [[NSMutableString alloc] init];
for(int i = 0; i < [entityObjects count]-1; i++){
[nameAttributes appendString:[NSString stringWithFormat:#"%#, ", [entityObjects objectAtIndex:i].name]];
}
[nameAttributes appendString:[NSString stringWithFormat:#"%#", [entityObjects lastObject].name]];
If you have an NSArray *objects of Core Data objects, each of which has a name attribute, then you can use
NSArray *names = [objects valueForKey:#"name"];
to get a new array with all the names, which you can then concatenate with
NSString *allNames = [names componentsJoinedByString:#","];
You can simply do like that,
NSString *toCollectString =#"";
for(int k =0;k<self.arrayHoldingObjects.count;k++)
{
ModelName *model = [self.arrayHoldingObjects objectAtIndex:k];
NSString *str = model.name;
toCollectString = [toCollectString stringByAppendingString:str];
}
You will get the names in toCollectString.
I have an Iphone app that uses alot of int values that will increment on IBActions, I want to save the int values to an array when the app closes so that these values are stores and used when the app is reopened. I am not sure how to write int values into an array. Functionally, I am getting this to wort with text field but not integers i.e.
int count;
code used:
NSArray *values = [[NSArray alloc] initWithObjects:fieldOne.text,fieldTwo.text,count, nil];
This gives an "Assignment makes integer from pointer without cast" message.
Is there anyway to write already stored int values into and array?
code I used is as follows:
I thinks its ok until the calling the data into the array. I have commented out some failed efforts
-(NSString *) saveFilePath{
NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
return [[path objectAtIndex:0] stringByAppendingPathComponent:#"savefile.plist"];
}
-(void) applicationDidEnterBackground: (UIApplication *) application{
//NSNumber *num = [[NSNumber alloc]initWithInt:count];
NSArray *values = [[NSArray alloc] initWithObjects:fieldOne.text,fieldTwo.text,[NSNumber numberWithInt:count],nil];
[values writeToFile:[self saveFilePath] atomically:YES];
[values release];
}
- (void)viewDidLoad {
//NSNumber *num = [[NSNumber alloc]initWithInt:count];
NSString *myPath = [self saveFilePath];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:myPath];
if (fileExists) {
NSArray *values = [[NSArray alloc] initWithContentsOfFile:myPath];
fieldOne.text = [values objectAtIndex:0];
fieldTwo.text = [values objectAtIndex:1];
//[NSNumber count intValue] = [values objectAtIndex:2];
[values release];
}
UIApplication *myApp = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector (applicationDidEnterBackground:)name:UIApplicationDidEnterBackgroundNotification object:myApp];
[super viewDidLoad];
}
Thank you for your help.
You should use NSNumber so something like:
NSNumber *num = [NSNumber numberWithInt:int];
which will give you an object containing your int. To read back from it, use [num intValue]
Create a NSNumber object with your count as its value and put the object into your array. NSArrays need to be arrays of objects.
Container classes work with Objects not fundamental types. You have to wrap fundamental types in NSNumber (numbers) , NSData etc.
I get that error EXC_BAD_ACESS at the following line:
NSString *titleVarName = [[NSString alloc] initWithFormat:#"%#%#",#"occasionTitle",i];
Here is the for loop where the above code line is located:
for (i=0; i < count; ++i)
{
//Save the occasionS details to NSUserDefaults
NSString *titleVarName = [[NSString alloc] initWithFormat:#"%#%#",#"occasionTitle",i];
NSString *dateVarName = [[NSString alloc] initWithFormat:#"%#%#",#"occasionDate",i];
NSString *imageVarName = [[NSString alloc] initWithFormat:#"%#%#",#"occasionImage",i];
[[NSUserDefaults standardUserDefaults] setValue:[[[self displayedObjects] objectAtIndex:i]
title] forKey:titleVarName];
[[NSUserDefaults standardUserDefaults] setValue:[[[self displayedObjects] objectAtIndex:i]
date] forKey:dateVarName];
[[NSUserDefaults standardUserDefaults] setValue:[[[self displayedObjects] objectAtIndex:i]
imagePath] forKey:imageVarName];
//release
[titleVarName release];
[dateVarName release];
[imageVarName release];
[self dismissModalViewControllerAnimated:YES];
}
Isn't ok to alloc objects and release them inside a for loop?
You need to use %d or %i specifier instead of %# to specify an integer. If %# is used with int then it will try to access the object at the address specified by the int. For example, if the value of i is one then it is trying to access the object at address one which will cause a bad access.
NSString *titleVarName = [[NSString alloc] initWithFormat:#"%#%d",#"occasionTitle",i];
And also you don't need alloc and release here, though that is not the reason of bad access. You can use a convenience constructor.
NSString *titleVarName = [NSString stringWithFormat:#"occasionTitle%d", i];
// release not required
Do the same for dateVarName and imageVarName too.
Assuming i is an int, that line should be
NSString *titleVarName = [[NSString alloc] initWithFormat:#"%#%i",#"occasionTitle",i];
%# is used for Cocoa objects, not primitives like an int, float or bool;
Use the %# format specifier only for NSObject objects.
As i is an integer in your code, you have to use %d or %i for integers.
Moreover, there is no need to include the string using %#, you can use the static string directly in your format string:
NSString *titleVarName = [[NSString alloc] initWithFormat:#"occasionTitle%i",i];
Okay, so, I'm doing a simple lookup. I have an array of NSString objects and a string to search for in the array's elements.
It all seems to work up until I try to add a match to a new mutable array made to hold the search results. The stringHolder variable gets the string, and resultsCollectorArray even get the right number of new elements, but each element is empty and "out of range". Here's the method:
#implementation NSArray (checkForString)
-(NSMutableArray *) checkForString: (NSString *) matchSought
{
long unsigned numberofArrayElements;
long unsigned loop = 0;
NSRange searchResults;
NSMutableArray * resultCollectorArray = [[NSMutableSet alloc] init];
id stringHolder;
numberofArrayElements = [self count];
while (loop < numberofArrayElements) {
searchResults.length = 0;
searchResults = [[self objectAtIndex: loop] rangeOfString: matchSought options:NSCaseInsensitiveSearch];
if (searchResults.length > 0) {
stringHolder = [self objectAtIndex: loop];
[resultCollectorArray addObject: stringHolder];
}
loop++;
}
return [resultCollectorArray autorelease];
}
Once we get back to the main portion of the program, I get an unrecognized selector sent to the mutable array that was supposed to receive the result of the method. Here's the main section:
#import <Foundation/Foundation.h>
#import "LookupInArray.h"
int main (int argc, const char * argv[])
{
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
NSString *testString = [[NSString alloc] initWithString: #"ab"];
NSMutableString * resultString = [[NSString alloc] init];
NSArray * theArray = [[NSArray alloc] initWithObjects: ..., nil]; // Actual code has the objects
NSMutableArray *resultArray = [[NSMutableArray alloc] init];
NSUInteger arrayCount = 0;
unsigned long loops = 0;
resultArray = [theArray checkForString: testString];
arrayCount = [resultArray count];
while (loops < arrayCount){
resultString = [resultArray objectAtIndex: loops]; // Here's where we get the unrecognized selector.
NSLog(#"%#", resultString);
loops++;
}
[pool drain]; // Also, I'll release the objects later. I just want to get what's above working first.
return 0;
}
I've searched the other answers (for hours now), but didn't seen anything that solved the issue.
Any and all help would be really appreciated.
And thanks beforehand.
NSMutableArray * resultCollectorArray = [[NSMutableSet alloc] init]; is so incorrect. You are creating a mutable set and assigning it to a mutable array.
You are getting unrecognized selector because objectAtIndex: is not a valid selector for NSMutableSet. Make that statement,
NSMutableArray * resultCollectorArray = [[NSMutableArray alloc] init];
A Better way
NSArray * filteredArray = [array filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"SELF contains[cd] %#", searchString]];
You can directly filter the array using predicates. This way you do this in a single step. :)
Is there any way to create a new
NSString from a format string like #"xxx=%#, yyy=%#" and a NSArray of objects?
In the NSSTring class there are many methods like:
- (id)initWithFormat:(NSString *)format arguments:(va_list)argList
- (id)initWithFormat:(NSString *)format locale:(id)locale arguments:(va_list)argList
+ (id)stringWithFormat:(NSString *)format, ...
but non of them takes a NSArray as an argument, and I cannot find a way to create a va_list from a NSArray...
It is actually not hard to create a va_list from an NSArray. See Matt Gallagher's excellent article on the subject.
Here is an NSString category to do what you want:
#interface NSString (NSArrayFormatExtension)
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments;
#end
#implementation NSString (NSArrayFormatExtension)
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments
{
char *argList = (char *)malloc(sizeof(NSString *) * arguments.count);
[arguments getObjects:(id *)argList];
NSString* result = [[[NSString alloc] initWithFormat:format arguments:argList] autorelease];
free(argList);
return result;
}
#end
Then:
NSString* s = [NSString stringWithFormat:#"xxx=%#, yyy=%#" array:#[#"XXX", #"YYY"]];
NSLog( #"%#", s );
Unfortunately, for 64-bit, the va_list format has changed, so the above code no longer works. And probably should not be used anyway given it depends on the format that is clearly subject to change. Given there is no really robust way to create a va_list, a better solution is to simply limit the number of arguments to a reasonable maximum (say 10) and then call stringWithFormat with the first 10 arguments, something like this:
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments
{
if ( arguments.count > 10 ) {
#throw [NSException exceptionWithName:NSRangeException reason:#"Maximum of 10 arguments allowed" userInfo:#{#"collection": arguments}];
}
NSArray* a = [arguments arrayByAddingObjectsFromArray:#[#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X",#"X"]];
return [NSString stringWithFormat:format, a[0], a[1], a[2], a[3], a[4], a[5], a[6], a[7], a[8], a[9] ];
}
Based on this answer using Automatic Reference Counting (ARC): https://stackoverflow.com/a/8217755/881197
Add a category to NSString with the following method:
+ (id)stringWithFormat:(NSString *)format array:(NSArray *)arguments
{
NSRange range = NSMakeRange(0, [arguments count]);
NSMutableData *data = [NSMutableData dataWithLength:sizeof(id) * [arguments count]];
[arguments getObjects:(__unsafe_unretained id *)data.mutableBytes range:range];
NSString *result = [[NSString alloc] initWithFormat:format arguments:data.mutableBytes];
return result;
}
One solution that came to my mind is that I could create a method that works with a fixed large number of arguments like:
+ (NSString *) stringWithFormat: (NSString *) format arguments: (NSArray *) arguments {
return [NSString stringWithFormat: format ,
(arguments.count>0) ? [arguments objectAtIndex: 0]: nil,
(arguments.count>1) ? [arguments objectAtIndex: 1]: nil,
(arguments.count>2) ? [arguments objectAtIndex: 2]: nil,
...
(arguments.count>20) ? [arguments objectAtIndex: 20]: nil];
}
I could also add a check to see if the format string has more than 21 '%' characters and throw an exception in that case.
#Chuck is correct about the fact that you can't convert an NSArray into varargs. However, I don't recommend searching for the pattern %# in the string and replacing it each time. (Replacing characters in the middle of a string is generally quite inefficient, and not a good idea if you can accomplish the same thing in a different way.) Here is a more efficient way to create a string with the format you're describing:
NSArray *array = ...
NSAutoreleasePool *pool = [NSAutoreleasePool new];
NSMutableArray *newArray = [NSMutableArray arrayWithCapacity:[array count]];
for (id object in array) {
[newArray addObject:[NSString stringWithFormat:#"x=%#", [object description]]];
}
NSString *composedString = [[newArray componentsJoinedByString:#", "] retain];
[pool drain];
I included the autorelease pool for good housekeeping, since an autoreleased string will be created for each array entry, and the mutable array is autoreleased as well. You could easily make this into a method/function and return composedString without retaining it, and handle the autorelease elsewhere in the code if desired.
This answer is buggy. As noted, there is no solution to this problem that is guaranteed to work when new platforms are introduced other than using the "10 element array" method.
The answer by solidsun was working well, until I went to compile with 64-bit architecture. This caused an error:
EXC_BAD_ADDRESS type EXC_I386_GPFLT
The solution was to use a slightly different approach for passing the argument list to the method:
+ (id)stringWithFormat:(NSString *)format array:(NSArray*) arguments;
{
__unsafe_unretained id * argList = (__unsafe_unretained id *) calloc(1UL, sizeof(id) * arguments.count);
for (NSInteger i = 0; i < arguments.count; i++) {
argList[i] = arguments[i];
}
NSString* result = [[NSString alloc] initWithFormat:format, *argList] ;// arguments:(void *) argList];
free (argList);
return result;
}
This only works for arrays with a single element
There is no general way to pass an array to a function or method that uses varargs. In this particular case, however, you could fake it by using something like:
for (NSString *currentReplacement in array)
[string stringByReplacingCharactersInRange:[string rangeOfString:#"%#"]
withString:currentReplacement];
EDIT: The accepted answer claims there is a way to do this, but regardless of how fragile this answer might seem, that approach is far more fragile. It relies on implementation-defined behavior (specifically, the structure of a va_list) that is not guaranteed to remain the same. I maintain that my answer is correct and my proposed solution is less fragile since it only relies on defined features of the language and frameworks.
For those who need a Swift solution, here is an extension to do this in Swift
extension String {
static func stringWithFormat(format: String, argumentsArray: Array<AnyObject>) -> String {
let arguments = argumentsArray.map { $0 as! CVarArgType }
let result = String(format:format, arguments:arguments)
return result
}
}
Yes, it is possible. In GCC targeting Mac OS X, at least, va_list is simply a C array, so you'll make one of ids, then tell the NSArray to fill it:
NSArray *argsArray = [[NSProcessInfo processInfo] arguments];
va_list args = malloc(sizeof(id) * [argsArray count]);
NSAssert1(args != nil, #"Couldn't allocate array for %u arguments", [argsArray count]);
[argsArray getObjects:(id *)args];
//Example: NSLogv is the version of NSLog that takes a va_list instead of separate arguments.
NSString *formatSpecifier = #"\n%#";
NSString *format = [#"Arguments:" stringByAppendingString:[formatSpecifier stringByPaddingToLength:[argsArray count] * 3U withString:formatSpecifier startingAtIndex:0U]];
NSLogv(format, args);
free(args);
You shouldn't rely on this nature in code that should be portable. iPhone developers, this is one thing you should definitely test on the device.
- (NSString *)stringWithFormat:(NSString *)format andArguments:(NSArray *)arguments {
NSMutableString *result = [NSMutableString new];
NSArray *components = format ? [format componentsSeparatedByString:#"%#"] : #[#""];
NSUInteger argumentsCount = [arguments count];
NSUInteger componentsCount = [components count] - 1;
NSUInteger iterationCount = argumentsCount < componentsCount ? argumentsCount : componentsCount;
for (NSUInteger i = 0; i < iterationCount; i++) {
[result appendFormat:#"%#%#", components[i], arguments[i]];
}
[result appendString:[components lastObject]];
return iterationCount == 0 ? [result stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]] : result;
}
Tested with format and arguments:
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX", #"YYY", #"ZZZ"];
Result: xxx=XXX, yyy=YYY last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX", #"YYY"];
Result: xxx=XXX, yyy=YYY last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[#"XXX"];
Result: xxx=XXX last component
NSString *format = #"xxx=%#, yyy=%# last component";
NSArray *arguments = #[];
Result: last component
NSString *format = #"some text";
NSArray *arguments = #[#"XXX", #"YYY", #"ZZZ"];
Result: some text
I found some code on the web that claims that this is possible however I haven't managed to do it myself, however if you don't know the number of arguments in advance you also need to build the format string dynamically so I just don't see the point.
You better off just building the string by iterating the array.
You might find the stringByAppendingString: or stringByAppendingFormat: instance method handy .
One can create a category for NSString and make a function which receives a format, an array and returns the string with replaced objects.
#interface NSString (NSArrayFormat)
+ (NSString *)stringWithFormat:(NSString *)format arrayArguments:(NSArray *)arrayArguments;
#end
#implementation NSString (NSArrayFormat)
+ (NSString *)stringWithFormat:(NSString *)format arrayArguments:(NSArray *)arrayArguments {
static NSString *objectSpecifier = #"%#"; // static is redundant because compiler will optimize this string to have same address
NSMutableString *string = [[NSMutableString alloc] init]; // here we'll create the string
NSRange searchRange = NSMakeRange(0, [format length]);
NSRange rangeOfPlaceholder = NSMakeRange(NSNotFound, 0); // variables are declared here because they're needed for NSAsserts
NSUInteger index;
for (index = 0; index < [arrayArguments count]; ++index) {
rangeOfPlaceholder = [format rangeOfString:objectSpecifier options:0 range:searchRange]; // find next object specifier
if (rangeOfPlaceholder.location != NSNotFound) { // if we found one
NSRange substringRange = NSMakeRange(searchRange.location, rangeOfPlaceholder.location - searchRange.location);
NSString *formatSubstring = [format substringWithRange:substringRange];
[string appendString:formatSubstring]; // copy the format from previous specifier up to this one
NSObject *object = [arrayArguments objectAtIndex:index];
NSString *objectDescription = [object description]; // convert object into string
[string appendString:objectDescription];
searchRange.location = rangeOfPlaceholder.location + [objectSpecifier length]; // update the search range in order to minimize search
searchRange.length = [format length] - searchRange.location;
} else {
break;
}
}
if (rangeOfPlaceholder.location != NSNotFound) { // we need to check if format still specifiers
rangeOfPlaceholder = [format rangeOfString:#"%#" options:0 range:searchRange];
}
NSAssert(rangeOfPlaceholder.location == NSNotFound, #"arrayArguments doesn't have enough objects to fill specified format");
NSAssert(index == [arrayArguments count], #"Objects starting with index %lu from arrayArguments have been ignored because there aren't enough object specifiers!", index);
return string;
}
#end
Because NSArray is created at runtime we cannot provide compile-time warnings, but we can use NSAssert to tell us if number of specifiers is equal with number of objects within array.
Created a project on Github where this category can be found. Also added Chuck's version by using 'stringByReplacingCharactersInRange:' plus some tests.
Using one million objects into array, version with 'stringByReplacingCharactersInRange:' doesn't scale very well (waited about 2 minutes then closed the app). Using the version with NSMutableString, function made the string in about 4 seconds. The tests were made using simulator. Before usage, tests should be done on a real device (use a device with lowest specs).
Edit: On iPhone 5s the version with NSMutableString takes 10.471655s (one million objects); on iPhone 5 takes 21.304876s.
Here's the answer without explicitly creating an array:
NSString *formattedString = [NSString stringWithFormat:#"%# World, Nice %#", #"Hello", #"Day"];
First String is the target string to be formatted, the next string are the string to be inserted in the target.
No, you won't be able to. Variable argument calls are solved at compile time, and your NSArray has contents only at runtime.