I have a NSMutableArray:
NSMutableArray *temp = //get list from somewhere.
Now there is one method objectAtIndex which returns the object at specified index.
What I want to do is that, I want to first check whether an object at specified index exists or not. If it exists than I want to fetch that object. Something like:
if ([temp objectAtIndex:2] != nil)
{
//fetch the object
}
But I get exception at the if statement saying that index beyond bound.
Please anyone tell me how to achieve this.
you cannot have 'empty' slots in an NSArray. If [myArray count]==2 ie array has two elements then you know for sure that there is an object at index 0 and an object at index 1. This is always the case.
Check the length first using the count method.
if ([temp count] > indexIWantToFetch)
id object = [temp objectAtIndex:indexIWantToFetch];
you could do this way:
When you initialize, do something like:
NSMutableArray *YourObjectArray = [[NSMutableArray alloc] init];
for(int index = 0; index < desiredLength; index++)
{
[YourObjectArray addObject:[NSNull null]];
}
Then when you want to add but check if it already exists, do something like this:
YourObject *object = [YourObjectArray objectAtIndex:index];
if ((NSNull *) object == [NSNull null])
{
/// TODO get your object here..
[YourObjectArray replaceObjectAtIndex:index withObject:object];
}
Just check that the index is >= 0 and < count
Returns the number of objects currently in the receiver.
- (NSUInteger)count
int arrayEntryCount = [temp count];
First of all you check the length of array-
NSMutableArray *temp = //get list from somewhere.
now check-
if(temp length)
{
Your objectclass *obj = [temp objectAtIndex:indexnumber];
// indexnumber is 0,1,2 ,3 or anyone...
}
Related
The title pretty much says it all, but just to clarify: I have an NSMutableDictonary containing several NSMutableArrays. What I would like to do is find any value that is present in multiple arrays (there will not be any duplicates in a single array) and return that value. Can someone please help? Thanks in advance!
Edit: For clarity's sake I will specify some of my variables:
linesMutableDictionary contains a list of Line objects (which are a custom NSObject subclass of mine)
pointsArray is an array inside each Line object and contains the values I am trying to search through.
Basically I am trying to find out which lines share common points (the purpose of my app is geometry based)
- (NSValue*)checkForDupes:(NSMutableDictionary*)dict {
NSMutableArray *derp = [NSMutableArray array];
for (NSString *key in [dict allKeys]) {
Line *temp = (Line*)[dict objectForKey:key];
for (NSValue *val in [temp pointsArray]) {
if ([derp containsObject:val])
return val;
}
[derp addObjectsFromArray:[temp pointsArray]];
}
return nil;
}
this should work
If by duplicates you mean returning YES to isEqual: you could first make an NSSet of all the elements (NSSet cannot, by definition, have duplicates):
NSMutableSet* allElements = [[NSMutableSet alloc] init];
for (NSArray* array in [dictionary allValues]) {
[allElements addObjectsFromArray:array];
}
Now you loop through the elements and check if they are in multiple arrays
NSMutableSet* allDuplicateElements = [[NSMutableSet alloc] init];
for (NSObject* element in allElements) {
NSUInteger count = 0;
for (NSArray* array in [dictionary allValues]) {
if ([array containsObject:element]) count++;
if (count > 1) {
[allDuplicateElements addObject:element];
break;
}
}
}
Then you have your duplicate elements and don't forget to release allElements and allDuplicateElements.
I have a NSMutable Array and was trying to find the index number of the last object in this array. I tried this, but it feels cumbersome:
int currentCount = [[[self.myLibrary objectAtIndex:currentNoteBookNumber] tabColours] count];
NSLog(#"Number of tab colours total: %i", currentCount);
NSLog(#"Index number of last object: %i", currentCount-1);
Is there another way of doing this? The context of my problem is that I need to determine the last object in order to change it:
replaceObjectAtIndex:[last object] withObject: ...
Thanks!
If you need the index, then that is the way to do it (int lastIndex = [array count] - 1;). If you just want to replace the last object with a different object however, you can do:
[array removeLastObject];
[array addObject: newLastObject];
Try this:
[myArray replaceObjectAtIndex:[myArray count]-1 withObject:someNewObject];
If you add objects to your NSMutableArray with addObjects: method it always put elements at the end. When you removeObjectAtIndex:index it automatically shift down on 1 position all elements with indexes > index. That is why the last object in array is always have index [array count] - 1. I do not tell you about replacing objects, I just tell about adding objects.
int index=[*yourarrayname* indexOfObject:[*yourarrayname* lastObject]];
NSLog(#"index=%d",index);
Use this snippet:
int lastIndex = [YOUR_ARRAY count] - 1;
this will gives you last index of your array.
I have an NSMutableArray which only lasts during the session.
Currently I create it like this
NSMutableArray *temp = [[NSMutableArray alloc] initWithCapacity:10];
[self setScoreArray:temp];
[temp release];
Problem is when I go to check each index I'm getting an array outofbounds error
NSNumber *previousScore = [[self scoreArray] objectAtIndex:[self quizNum]];
if ( previousScore != nil )
{
[self clearQuizBtns];
NSInteger previousScoreValue = [previousScore integerValue];
[self selectButtonAtTag:previousScoreValue];
}else {
[self clearQuizBtns];
}
I've read in other posts that initWithCapacity doesn't actually create the array. So what can I populate the array with initially?
Thanks in advance.
Two ways:
first: to initiate array with default values of NSNull class
NSMutableArray *temp = [[NSMutableArray alloc] initWithCapacity:10];
for (int i = 0 ; i < 10 ; i++)
{
[temp insertObject:[NSNull null] atIndex:i];
}
[self setScoreArray:temp];
[temp release];
and then to check: if object is kind of NSNull class means it was a never set before
id previousScore = [[self scoreArray] objectAtIndex:[self quizNum]];
if (![previousScore isKindOfClass:[NSNull class]])
{
[self clearQuizBtns];
NSInteger previousScoreValue = [(NSNumber *)previousScore integerValue];
[self selectButtonAtTag:previousScoreValue];
}else {
[self clearQuizBtns];
}
second: store scores in NSMutableDictionary and use NSNumber's as keys
// scoreDictionary property of NSMutableDictionary class must be declared in self
NSNumber *previousScore = [self.scoreDictionary objectForKey:[NSNumber numberWithInt:[self quizNum]]];
if (previousScore != nil)
{
[self clearQuizBtns];
NSInteger previousScoreValue = [previousScore integerValue];
[self selectButtonAtTag:previousScoreValue];
}else {
[self clearQuizBtns];
}
NSArray does not support "holes". The capacity is just a hint to the initializer.
You could either fill the array with placeholder objects or, more typically, change your algorithm to either fully prepopulate the array or to lazy load it linearly.
Your problem seems to be that you're never actually setting any score in the score array.. are you? NSArrays have an actual count of items in them, and accessing an index beyond that count will blow up, as you've seen. If there will only ever be a fixed (small) number of scores, like 10, then you could set them all initially to something default like:
for (int i = 0; i < 10; i++) {
[temp addObject:[NSNumber numberWithInt:0]];
}
P.S. -initWithCapacity does "create the array", it just doesn't create any objects in the array. The capacity is a hint only.
Using the arrayWithObject: or arrayWithObjects: methods can provide an array with pre-populated values.
One cool thing about NSMutableArrays is that you can just do an "init" and the array will handle adding and removing objects on the fly. Remember that you generally addObject: or removeObjectAtIndex: when dealing with mutable arrays.
I am trying to detect if an array isn't empty in order to be able to do a certain call.
I tried using if (![array ==nil]) however that doesn't compile.
I'm sure there is a really easy explanation to this.
Update
If array is empty I want to do this:
array = [[NSMutableArray alloc]init];
If it has an object I want to do this:
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
If you declared it but did not assign anything to it at all:
NSMutableArray *array;
Then the array will be nil, meaning it isn't there at all so you can't say if it's empty or not, so you can't check anything.
If you did assign something to it, and you want to find out if the existing array is empty or not, that would depend on how you created it first.
If the array was assigned from some convenience method, it's autoreleased, so just do this:
if ([array count] == 0) {
array = [[NSMutableArray alloc] init];
} else {
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
}
If the array was assigned from an init or copy method, or it was retained previously, store the count in a temporary variable, release the array and use the temporary variable to decide what to do:
NSInteger count = [array count];
[array release];
if (count == 0) {
array = [[NSMutableArray alloc] init];
} else {
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
}
In your case I'd always use without differentation
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
and set the default value in the user defaults to an empty array right away at program start before accessing the defaults (from Apple's example):
+ (void)initialize{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSDictionary *appDefaults = [NSDictionary
dictionaryWithObject:[NSArray array] forKey:#"MyFavorites"];
[defaults registerDefaults:appDefaults];
}
See Apple's doc on this.
Supposing you are talking about NSArray, if myArray has not been properly alloced+initialized (what you are trying to check) its reference will be nil, so you can do:
if(myArray) //or even if(myArray != nil) since myArray will be a pointer
{
//properly inizialized
}
else
{
//not properly inited
}
If it's been inited on the other hand, you can test its emptiness by checking the count property which returns the number of elements it contains
if([myArray > 0])
//there is at least one element
}
else
{
//no elements
}
you can use count function of NSArray. it will work on NSMutableArray too....
syntext will be,
int ct=[array count];
ct will have number of items in array.
if it us empty it will be Zero
I am having array called stored and I want to access their indexes so that I can select them individually to do my operations.
If I want to print their indexes, what should I do?
use NSArray's indexOfObject: method. Such as the following:
NSUInteger fooIndex = [someArray indexOfObject: someObject];
int totalElements = [anArray count];
for(int i=0; i < totalElements; i++)
{
data = [myArray indexOfObject:i];
}
The above code will give you the data if you pass in the index
NSString *haystackText = #"Hello World";
int totalElements = [anArray count];
for(int i=0; i < totalElements; i++)
{
BOOL result = [haystackText caseInsensitiveCompare:[myArray objectAtIndex:i] == NSOrderedSame;
if(result)
{
NSUInteger fooIndex = [myArray indexOfObject: haystackText];
return fooIndex;
}
}
The code above will first find the element in the array and if it exists then return the index.
[array indexOfObject:object]
returns index of "object"
You can use indexOfObject method to get the index of element.
for example
This will give you index of your object
NSInteger index = [yourArray indexOfObject:objectName];
This worked for me. Hope this helps.
You can get a list of the indexes by using the count method which returns the number of elements in the array:
int numElements = [myArray count];
I'll leave it as an exercise to print out the actual index values :)
This article has some great examples of how to iterate over an array. Then, inside the loop, you can use NSLog to print the index.