I have a basic question. I need to use intemediate array in loop. This is my code:
NSMutableArray *interArray = [[NSMutableArray alloc] initWithCapacity:2];
NSMutableArray *finalyArray = [[NSMutableArray alloc] init];
NSInteger a;
for(int j=0; j<5; j++)
{ [interArray removeAllObjects];
for(int i=0; i<2; i++)
{
a = [array ObjectAtInde:i]; // this is existing array
[interArray addObject:a];
}
[finalyArray addObject:interArray];
}
but when i delete objects in intermediate array I get empty Arrays in finaly Array. How to fix it? Thanks
The reason it won't work as you expect is because interArray is a reference to an object which you empty and fill in the loop and then add to the finalyArray, however you are adding the same intermediate array each time.
What you want to do it create a new intermediate array within the loop and therefore each intermediate array will be a separate object:
NSMutableArray *finalyArray = [[NSMutableArray alloc] init];
NSInteger a;
for(int j=0; j<5; j++)
{
NSMutableArray *interArray = [[NSMutableArray alloc] initWithCapacity:2];
for(int i=0; i<2; i++)
{
a = [array ObjectAtIndex:i]; // this is existing array
[interArray addObject:a];
}
[finalyArray addObject:interArray];
}
(Note this code won't work anyway as you cannot store NSInteger in a collection class without first wrapping it in a NSNumber object).
Related
I have two codes. Not working is the following:
NSMutableArray *tmpArray = [[NSMutableArray alloc] init];
for (int i=0; i<[dataSetArray count]; i++) {
tmpArray = (NSMutableArray *) [dataSetArray objectAtIndex:i];
// OR use: tmpArray = dataSetArray[i]
... doing stuff
[tmpArray replaceObjectAtIndex:0 withObject:tmpStr];
}
While this works:
for (int i=0; i<[dataSetArray count]; i++) {
NSMutableArray *tmpArray = [[NSMutableArray alloc] initWithArray:[dataSetArray objectAtIndex:i]];
... doing stuff
[tmpArray replaceObjectAtIndex:0 withObject:tmpStr];
}
Two questions:
The first code doesn't yield an NSMutableArray. Why? I declare it
above.
Is there a better way to obtain the same result. I just
dislike defining variables in a loop. This makes the code
unreadable.
--- edit:
Here the full code:
Datatypes are:
dataSetArray: NSMutableArray. However, its contents (i.e. dataSetArray[i]) are NSArrays (I read them into the program from an excel file).
NSString *tmpStr = [[NSString alloc] init];
for (int i=0; i<[dataSetArray count]; i++) {
NSMutableArray *tmpArray = [[NSMutableArray alloc] initWithArray:[dataSetArray objectAtIndex:i]];
for (int j=0; j<[tmpArray count]; j++) {
if ( [dataSetArray[0][j] isEqualToString:#"Number"] ) {continue;}
tmpStr = (NSString *) [tmpArray objectAtIndex:j];
// replace single backslash by double-backslash:
tmpStr = [tmpStr stringByReplacingOccurrencesOfString:#"\\" withString:#"\\\\"];
// replace first dollar sign by "<p>\\[" and second by "\\]</p>"
// Use a methode defined in the NSString+Extension
tmpStr = [tmpStr replaceTexFormulaSigns:tmpStr];
//NSLog(#"j=%d", j);
//NSLog(#"tmpArray is of type: %#", [tmpArray class]);
//NSLog(#" tmpStr is of type: %#", [tmpStr class]);
[tmpArray replaceObjectAtIndex:j withObject:tmpStr];
}
[dataSetArray replaceObjectAtIndex:i withObject:tmpArray];
}
So even if I use your suggestion, I am still facing the same problem with the inner array.
The first code doesn't yield a NSMutableArray. Why? I declare it above.
The declaration of the reference variable tmpArray does not change the type of the referred object. It is still an (immutable) array.
The creation of the mutable array at the very beginning of the first snippet is without any meaning, because the reference to it is overridden.
Is there a better way to obtain the same result. I just dislike defining variables in a loop. This makes the code unreadable.
Yes. The second example works in a way, but do something completely different. (It always creates a new array with a single item in it. No, that's not true. It shouldn't compile at all.)
You should do:
NSMutableArray *tmpArray = [dataSetArray mutableCopy];
for (int i=0; i<[dataSetArray count]; i++)
{
…
[tmpArray replaceObjectAtIndex:i withObject:tmpStr];
}
You should really get some additional knowledge about objects and object references.
I define a NSMutableArray *nameArray in .h file. And add strings using this nameArray in a for loop in .m file like below:
for (int i=0; i<[data count]; i++) {
NSDictionary* place = [data objectAtIndex:i];
NSString *name=[place objectForKey:#"name"];
_nameArray = [[NSMutableArray alloc] init];
[_nameArray addObject:name];
}
NSLog(#"After loop, Name is %#", _nameArray);
Actually, it should have several names in this array. But why it only output one name which was added in the array last?
You must create your array outside the loop, that is your problem.
// Init array
_nameArray = [[NSMutableArray alloc] init];
// Fill array
for (int i=0; i<[data count]; i++) {
NSDictionary* place = [data objectAtIndex:i];
NSString *name=[place objectForKey:#"name"];
[_nameArray addObject:name];
}
// Log array
NSLog(#"After loop, Name is %#", _nameArray);
All of your objects are added to an own array and only the last array will not be overwritten and is therefore in the log.
I'm doing this:
for(int i=0;i>count;i++)
{
NSArray *temp=[[NSArray alloc]initWIthObjects]i,nil];
NSLog(#"%i",temp);
}
It returns to me 0,1,2,3....counting one by one, but I want an array with appending these values {0,1,2,3,4,5...}.
This is not a big deal, but I'm unable to find it. I am new to iPhone.
NSMutableArray *myArray = [NSMutableArray array];
for(int i = 0; i < 10; i++) {
[myArray addObject:#(i)];
}
NSLog(#"myArray:\n%#", myArray);
This code is not doing what you want it to do for several reasons:
NSArray is not a "mutable" class, meaning it's not designed to be modified after it's created. The mutable version is NSMutableArray, which will allow you to append values.
You can't add primitives like int to an NSArray or NSMutableArray class; they only hold objects. The NSNumber class is designed for this situation.
You are leaking memory each time you are allocating an array. Always pair each call to alloc with a matching call to release or autorelease.
The code you want is something like this:
NSMutableArray* array = [[NSMutableArray alloc] init];
for (int i = 0; i < count; i++)
{
NSNumber* number = [NSNumber numberWithInt:i]; // <-- autoreleased, so you don't need to release it yourself
[array addObject:number];
NSLog(#"%i", i);
}
...
[array release]; // Don't forget to release the object after you're done with it
My advice to you is to read the Cocoa Fundamentals Guide to understand some of the basics.
A shorter way you could do is:
NSMutableArray *myArray = [NSMutableArray array];
for(int i = 0; i < 10; i++) {
[myArray addObject:#(i)];
}
NSLog(#"myArray:\n%#", myArray);
I used to be a Java Programmer, which the array need to declare the very first time, like this:
int[] anArray; // declares an array of integers
anArray = new int[10]; // allocates memory for 10 integers
I don't know whether the Objective C , NSMutableArray also give me this ability or not. Actually, I want to make a 10*10 array. thz in advance.
I try to do this:
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
myArray[i] = [[NSMutableArray alloc] initWithCapacity:10];
}
But it occurs errors, telling my incompatible type assignment.
The capacity field is seldom useful. The array will be expanded on demand anyway.
And the capacity field just tells the array how much memory you may use. The array's length is still 0.
But you can grow the array from empty:
for (int i = 0; i < 10; ++ i)
[myArray addObject:…];
To read and write to an element in an NSMutableArray, you need:
id x = [array objectAtIndex:i]; // x = array[i];
[array replaceObjectAtIndex:i withObject:y]; // array[i] = y;
You cannot subscript an NSArray directly.
Your code has memory leak. Unlike Java, ObjC doesn't use a GC unless you explicitly enable it (and ObjC on iPhoneOS doesn't have GC). ObjC manages memory by manual reference counting. Basically you need to ensure the ref count of stuff you don't own doesn't change in the process. See http://developer.apple.com/mac/library/documentation/cocoa/Conceptual/MemoryMgmt/MemoryMgmt.html for detail.
In your case, [[NSMutableArray alloc] …]; creates an object of ref count +1, then the assignment will take over the array, that means you don't own it any more, but the ref count is not balanced to 0, so this memory will not be properly deallocated. You need to use convenient methods such as [NSMutableArray array…] to create an object with ref count 0.
NSArray's can only store ObjC objects. int in C (ObjC) is a primitive, and cannot be stored into an NSArray. You have to box it into an NSNumber by [NSNumber numberWithInt:0]. You can get back the integer with -intValue.
To conclude, your code needs to be modified as:
-(NSMutableArray*)get10x10Array {
NSMutableArray* arr = [NSMutableArray array];
for (int i = 0; i < 10; ++ i) {
NSMutableArray* subarr = [NSMutableArray array];
for (int j = 0; j < 10; ++ j)
[subarr addObject:[NSNumber numberWithInt:0]];
[arr addObject:subarr];
}
return arr;
}
But ObjC is a superset of C. You can just use a plain 10x10 C array.
int arr[10][10];
You want a 10x10 array -- of what?
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
myArray[i] = [[NSMutableArray alloc] initWithCapacity:10];
}
But it occurs errors, telling my
incompatible type assignment.
Because you can't assign to myArray like that. myArray is an object that represents an array data structure. It is not a C array.
If you want a 10x10 array of a primitive data type, you can declare one like you would in C:
int myArray[10][10];
initWithCapacity: is what you want. It may look like
NSMutableArrat *array = [[NSMutableArray alloc] initWithCapacity:10];
You can't access Cocoa array objects with the bracket notation. Your second bit of code should be:
NSMutableArray *myArray = [[NSmutableArray alloc] initWithCapacity:10];
for (int i = 0; i < 10; i++) {
[myArray insertObject:[NSMutableArray arrayWithCapacity:10] atIndex:i]; // Note: not using myArray[i]!
}
There are two ways to do this.
Plain old C
If you want to store objects, you should use the id type instead of int.
int myarray[10][10];
myarray[5][2] = 412;
Objective-C
NSArray's are not meant to have spaces without objects, if you need them you could use [NSNull null], but if that's the case a C array would be better anyway.
NSMutableArray *myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i < 10; i++) {
NSMutableArray *innerArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int j=0; j < 10; j++) {
[innerArray addObject:[NSNull null]];
}
[myArray addObject:innerArray];
[innerArray release];
}
[[myArray objectAtIndex:5]
replaceObjectAtIndex:2 withObject:[NSNumber numberWithInteger:123]];
NSArray objects have a fixed size that cannot be changed once they have been initialised. NSMutableArray objects can change size. A 10×10 array is sometimes implemented as an NSArray containing 10 individual NSArray objects, each of these containing ten items. This quickly gets cumbersome, sometimes it is easier to resort back to plain C for such a task:
int tenByTen[10][10];
Or, you can use this:
typedef struct
{
int y[10];
} TenInts;
typedef struct
{
TenInts x[10];
} TenByTen;
Then you could do:
- (void) doSomethingWithTenByTen:(const TenByTen) myMatrix
{
NSLog ("%d", myMatrix.x[1].y[5]);
}
And you can also return them from methods:
- (TenByTen) mangleTenByTen:(const TenByTen) input
{
TenByTen result = input;
result.x[1].y[4] = 10000;
return result;
}
You want NSMutableArray +arrayWithCapacity:
Note that setting the initial capacity is merely an optimization - Mutable arrays expand as needed.
EDIT:
To do the 10x10 case,
myArray = [[NSMutableArray alloc] initWithCapacity:10];
for (int i=0; i<10; i++) {
NSMutableArray *subArray = [NSMutableArray arrayWithCapacity:10];
[myArray addObject:subArray];
for (int j = 0; j<10; j++) {
[subArray addObject:[NSNumber numberWithInt:0]];
}
}
Notes:
an array retains the objects added to it, so its not necessary to retain subArray
only objects (not primitive types like "int") can be added to an NSArray, hence the need for NSNumber numberWithInt:
you use methods like objectAtIndex: and replaceObjectAtIndex:withObject: to get/set a value from an NSArray, not array subscript ([]) syntax
See Apple refs for NSArray and NSMutableArray
You can use the following code to resize the NSMutableArray once it was created:
#interface NSMutableArray (Resizing)
- (NSMutableArray *)resize:(NSInteger)newSize;
#end
#implementation NSMutableArray (Resizing)
- (NSMutableArray *)resize:(NSInteger)newSize
{
int size = (newSize > [self count]) ? self.count : newSize;
NSMutableArray *array = [NSMutableArray arrayWithCapacity:size];
for (int i = 0; i < size; i++){
[array addObject:[self objectAtIndex:i]];
}
return array;
}
#end
How would I create a number of NSDictionary variables using an array's count?
This is basically what I came up with, but I'm not sure how to make this work with Objective-C syntax. doesntContainAnother is an NSArray. I want the names of the dictionaries to use the current value of loopInt.
int *loopInt = 0;
while (doesntContainAnother.count <= loopInt) {
NSMutableDictionary *[NSString stringWithFormat:#"loopDictionary%i", loopInt] = [[[NSMutableDictionary alloc] init] autorelease];
[NSString stringWithFormat:#"loopDictionary%i", loopInt] = [NSDictionary dictionaryWithObject:[array1 objectAtIndex:loopInt]
forKey:[array2 objectAtIndex:loopInt]];
loopInt = loopInt + 1;
}
Create a mutable array and loop until you reach the original array's count, creating a dictionary and adding it to the mutable array on each iteration.
Your code should look like this.
NSMutableArray *dictionaries = [[NSMutableArray alloc] init];
for (int i = 0; i < doesntContainAnother.count; i++) {
[dictionaries addObject:[NSMutableDictionary dictionaryWithObject:[array1 objectAtIndex:i] forKey:[array2 objectAtIndex:i]]];
}
The approach of creating variables with numbers at the end of their names is an antipattern and not even possible in Objective-C. It's equivalent to an array, but clunkier.
You need to create a mutable array, and then put the objects into the array. You can't create a variable with the same name as the contents of a string, as you have done. For example:
NSMutableArray *arr = [[NSMutableArray alloc] initWithCapacity:[doesntContainAnother count]];
int i = 0; // Note: type is int, not int*
for (i = 0; i < [doesntCountainAnother count]; i++) {
[arr addObject:[NSMutableDictionary dictionary]];
}
// Later...
NSMutableDictionary *d1 = [arr objectAtIndex:3];
Or if you want to pull them out of the list by name:
NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithCapacity:[doesntCountainAnother count]];
int i = 0;
for (i = 0; i < [doesntContainAnother count]; i++) {
[dict setObject:[NSMutableDictionary dictionary] forKey:[NSString stringWithFormat:#"loopDictionary%d", i]];
}
// Later...
NSMutableDictionary *d1 = [dict objectForKey:#"loopDictionary3"];
But the first way is likely the easiest.