How can I add object at specified index?
in my problem
NSMutableArray *substring
contains index and object alternatively
and I need to add it to the another array str according to index I getting from this array.
NSMutableArray *str=[NSMutableArray new];
if ([substrings containsObject:#"Category-Sequence:"])
{
NSString *index=[substrings objectAtIndex:5];
//[substrings objectAtIndex:5]
gives me integer position at which I need to add object in `str` array,
gives 5,4,8,2,7,1 etc
NSString *object=[substrings objectAtIndex:1];
//[substrings objectAtIndex:1] gives object,gives NSString type of object
[str insertObject:object atIndex:(index.intValue)];
}
please suggest some way to achieve it.
Thanks in advance!
Allocate the array first & then try to add objects in it.
NSMutableArray *str = [[NSMutableArray alloc]init];
if ([substrings containsObject:#"Category-Sequence:"])
{
NSString *index=[substrings objectAtIndex:5];
NSString *object=[substrings objectAtIndex:1];
[str insertObject:object atIndex:(index.intValue)];
}
Allocate the NSMutableArray before inserting objects into it:
NSMutableArray *strMutableArray = [[NSMutableArray alloc] init];
(You’ll also need to release it when you’re done if you’re not using ARC.)
Or you could also use a temporary object, if you don’t need to keep strMutableArray:
NSMutableArray *strMutableArray = [NSMutableArray array];
Then you can insert objects into the NSMutableArray.
Be careful with using indexes of and in different arrays, however. There might be a better way to do what you want.
Related
I created an NSMutableArray object by
NSMutableArray *array = [[NSMutableArray alloc]init];
and used method componentsSeperatedByString: as
array = [myString componentsSeperatedByString:#"++"];
but when I performed operation on array like,
[array removeAllObjects];
I got exception like "removeAllObjects unrecognized selector send to instance".
I solved this issue by modifying code like,
NSArray *components = [myString componentsSeperatedByString:#"++"];
array = [NSMutableArray arrayWithArray:components];
and I after that could perform operation like
[array removeAllObjects];
My doubt is why did NSMutableArray automaticaqlly converted to NSArray? How Can I avoid automatic type conversion like this, to prevent exceptions? Thanks in advance....
There is a mistake in your understanding of how Objective-C works. This line:
NSMutableArray *array = [[NSMutableArray alloc]init];
allocates and initializes the array, and the pointer array points to this object. Now, this line:
array = [myString componentsSeperatedByString:#"++"];
makes the array pointer to point to the new array returned by componentsSeparatedByString method. You loose the reference to your alloced and inited mutable array when you do this, and you create the memory leak if you don't use ARC.
This is happening because [myString componentsSeperatedByString:#"++"] returns an NSArray. You can try something like this:
array = [[myString componentsSeperatedByString:#"++"] mutableCopy];
or
array = [NSMutableArray arrayWithArray:[myString componentsSeperatedByString:#"++"]];
This is because – componentsSeparatedByString: returns a NSArray: https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html#//apple_ref/occ/instm/NSString/componentsSeparatedByString:
Do something like:
array = [NSMutableArray arrayWithArray:[myString componentsSeperatedByString:#"++"]];
On the line
array = [myString componentsSeperatedByString:#"++"];
you are replacing the NSMutableArray you allocated with a new NSArray (and leaking your NSMutableArray. Try using this:
NSMutableArray *array = [NSMutableArray arrayWithArray:[myString componentsSeperatedByString:#"++"]];
It's not converted, the array pointer could be UIButton* if you write something like
array = [self likeThatButton];
where likeThatButton is your method returning UIButton*. As always in objective c, NSMutableArray *array means only the Xcode will try to analyze your code and suggest convenient warnings and code completion.
An NSMutableArray instance won't be converted automatically.
The method componentsSeperatedByString returns an NSArray-Object. You should get a compiler warning when assigning the return-value to a NSMutableArray-Pointer.
i wanted to know how to add strings into an array.
I used the following methods but it is showing null.
1) [arrData addObject:[NSString stringWithString:strlast]];
2) [arrData addObject:strlast];
Thanks in advance
You can't add anything to an NSArray once it's created. You need to use an NSMutableArray if you want to make changes to it.
Update: You may actually have two problems.
Using an NSArray instead of an NSMutableArray when mutability is needed.
Not initializing the array object (either kind). If arrData is nil, you can happily send as many messages as you want to nil. Nothing will happen.
If it is showing null (nil) you need to make sure you set arrData somewhere in your code before trying to addObject:.
arrData = [[NSMutableArray alloc] init];
Also strlast is a string so use your second example, the first example is pointless.
[arrData addObject:strlast];
Did you allocate an array and assign it to arrData?
Try:
NSMutableArray *arrData = [NSMutableArray array];
NSString *string = #"My string";
[arrData addObject:string];
NSLog(#"%#", [arrData objectAtIndex:0]); //logs "My string"
If you're using a non-mutable array, you can also use arrayByAddingObject:
arrData = [arrData arrayByAddingObject: strlast];
but a mutable array is probably a better idea.
I want to split string into NSMutableArray
I know
- (NSArray *)componentsSeparatedByString:(NSString *)separator
is available but this one is for NSArray not for NSMutableArray.
I need because after spliting i want to remove element from array by using
-(void)removeObjectAtIndex:(NSUInteger)index
which is not possible with NSArray.
Thank you
You can also just get a mutable copy of the returned array:
NSMutableArray *array = [[myString componentsSeparatedByString:#"..."] mutableCopy];
Also, remember that copy, like alloc, does allocate new memory. So when used in non-ARC code you must autorelease the copied array or manually release it when you are done with it.
Make a new NSMutableArray using
NSArray *array = [NSString componentsSeparatedByString:#"..."];
NSMutableArray *mutable = [NSMutableArray arrayWithArray:array];
Create a NSMutableArray from the output NSArray created by componentsSeparatedByString.
NSMutableArray *mutableArray = [[NSMutableArray alloc] initWithArray:array];
I need to create a custom array:
In php I would define as follows:
$myarray[100][80] = 1;
But I don't know how to do it in objective-c...
I don't need an array [0][0],[0][1],[0][2], ... I only need concrete positions in this array [80][12], [147][444], [46][9823746],...
The content of these positions always will be = 1;
for this you would use a dictionary rather than an array as they are always 0,1,2 keyed so something along the lines of:
NSNumber *one = [NSNumber numberWithInt:1];
NSString *key = #"80,12";
NSDictionary *items = [NSDictionary dictionaryWithObject:one forKey:key];
Then to pull them out again you would use the objectForKey: method.
You cannot put ints directly into arrays or dictionaries that's why it is wrapped in the NSNumber object. To access the int after getting the NSNumber out of the dictionary you would use something like:
NSNumber tempNum = [items objectForKey:key];
int i = tempNum.intValue;
See the docs here for a full explanation of the NSDictionary class. Hope this helps...
I an not a PHP master but I believe in php arrays are not real arrays they are hash tables right?
Anyway, I think you are looking for NSDictionary or NSMutableDictionary class.
That looks more like a bitset than an array.
Allocating so many cells for that seems useless, so maybe you could revert the problem, and store the positions in an array.
Well in objective c we can use NSMutableArray to define 2-D arrays.
See the following code, it might help you
NSMutableArray *row = [[NSMutableArray alloc] initWithObjects:#"1", #"2", nil];
NSMutableArray *col = [[NSMutableArray alloc] init];
[col addObject:row];
NSString *obj = [[col objectAtIndex:0] objectAtIndex:0];
NSLog(#"%#", obj);
Is it acceptable to have a NSMutableArray within an NSDictionary? Or does the NSDictionary also have to be mutable?
The NSMutableArray will have values added to it at runtime, the NSDictionary will always have the same 2 NSMutableArrays.
Thanks,
Dan
Yes, it's perfectly acceptable. Keep in mind, the contents of the array are the pointers to your NSMutableArrays--those are what can't change in the immutable dictionary structure. What the pointers point to can change all you want. To wit:
NSMutableArray *arr = [[NSMutableArray alloc] init];
NSDictionary *dict = [NSDictionary dictionaryWithObject:arr forKey:#"test"];
[arr addObject:#"Hello"];
NSString *str = [[dict objectForKey:#"test"] objectAtIndex:0];
NSLog("%#", str);
It's quite acceptable. But, it's precisely the sort of setup that suggests you should seriously consider replacing the dictionary with an NSObject subclass that sports two properties for accessing the arrays.