I seem to be having a problem with the NSMutableArray.
Here's my code:
NSMutableArray *returnArray = [[NSMutableArray alloc] init];
while(condition) {
NSInteger temp = someNumber;
[returnArray addObject: temp];
}
But as soon as it hits the addObject message, the program seg faults. Any advice?
You can't add primitives like integers to an array, only objects (hence the name addObject:). If you want to add numbers, you have to convert them to an NSNumber, or one of the related classes.
You can only add objects to array and NSInteger is not an array.
NSMutableArray *returnArray = [[NSMutableArray alloc] init];
while(condition) {
[returnArray addObject: [NSNumber numberWithInt: someNumber]];
}
You need to wrap primitives such as NSInteger into an NSNumber class. You can do the following:
while(condition)
{
NSInteger temp = someNumber;
[returnArray addObject:#(temp)];
}
Or if your compiler doesn't support that syntax:
while(condition)
{
NSInteger temp = someNumber;
[returnArray addObject:[NSNumber numberWithInteger:temp]];
}
Related
How can I create array of floating point numbers in Objective-C?
Is it possible?
You can create a dynamic array (size decided at runtime, not compile time) in different ways, depending on the language you wish to use:
Objective-C
NSArray *array = [[NSArray alloc] initWithObjects:
[NSNumber numberWithFloat:1.0f],
[NSNumber numberWithFloat:2.0f],
[NSNumber numberWithFloat:3.0f],
nil];
...
[array release]; // If you aren't using ARC
or, if you want to change it after creating it, use an NSMutableArray:
NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:0];
[array addObject:[NSNumber numberWithFloat:1.0f]];
[array addObject:[NSNumber numberWithFloat:2.0f]];
[array addObject:[NSNumber numberWithFloat:3.0f]];
...
[array replaceObjectAtIndex:1 withObject:[NSNumber numberWithFloat:99.9f]];
...
[array release]; // If you aren't using ARC
Or using the new-ish Objective-C literals syntax:
NSArray *array = #[ #1.0f, #2.0f, #3.0f ];
...
[array release]; // If you aren't using ARC
C
float *array = (float *)malloc(sizeof(float) * 3);
array[0] = 1.0f;
array[1] = 2.0f;
array[2] = 3.0f;
...
free(array);
C++ / Objective-C++
std::vector<float> array;
array[0] = 1.0f;
array[1] = 2.0f;
array[2] = 3.0f;
For an dynamic approach you can use NSNumber object and add it to NSMutableArray, or if you need only static array then use suggestions from comments, or use standard C.
like:
NSMutableArray *yourArray = [NSMutableArray array];
float yourFloat = 5.55;
NSNumber *yourFloatNumber = [NSNumer numberWithFloat:yourFloat];
[yourArray addObject:yourFloatNumber];
and then to retrive:
NSNumber *yourFloatNumber = [yourArray objectAtIndex:0]
float yourFloat = [yourFloatNumber floatValue];
If you are using Xcode 4.4+, you can try this:
NSArray *a = #[ #1.1f, #2.2f, #3.3f];
Here is all new literals of LLVM Compiler 4.0.
How about something like this?
#interface DoubleArray : NSObject
#property(readonly, nonatomic) NSUInteger count;
#property(readonly, nonatomic) double *buffer;
- (instancetype)init NS_UNAVAILABLE;
- (instancetype)initWithCount:(NSUInteger)count NS_DESIGNATED_INITIALIZER;
- (double)valueAtIndex:(NSUInteger)idx;
- (void)setValue:(double)value atIndex:(NSUInteger)idx;
#end
#implementation DoubleArray
- (void)dealloc
{
if (_buffer != 0) {
free(_buffer);
}
}
- (instancetype)initWithCount:(NSUInteger)count
{
self = [super init];
if (self) {
_count = count;
_buffer = calloc(rows * columns, sizeof(double));
}
return self;
}
- (double)valueAtIndex:(NSUInteger)idx
{
return *(_buffer + idx);
}
- (void)setValue:(double)value atIndex:(NSUInteger)idx
{
*(_buffer + idx) = value;
}
#end
It's a basic array. You can extend this with more complex features like appending, indexed removal etc.
I'm writing an app for iPhone in objective-c. I want to declare an array that will hold different type of fields , like: int, NSString, bool.
Can I do it?
You can put whatever items in an NSArray as long as they are objects. So you have to wrap items that are not objects (such as BOOL, int and CGPoint) in some kind of objects such as NSNumber or NSValue.
NSMutableArray *array = [[NSMutableArray] alloc] init];
[array addObject:myString];
[array addObject:[NSNumber numberWithInt:1]];
[array addObject:[NSNumber numberWithFloat:1.0]];
[array addObject:[NSValue valueWithPoint:myPoint]]; // myPoint is a CGPoint
[array addObject:[NSValue valueWithRect:myRect]]; // myRect is a CGRect
Yes, you can
NSMutableArray *array = [NSMutableArray array];
NSString *string = #"str";
[array addObject:string]; //string
NSNumber *num = [NSNumber numberWithInt:1];
[array addObject:num]; //int
NSNumber *boolNum = [NSNumber numberWithBool:YES];
[array addObject:boolNum]; //bool
Use NSMutableArray.
NSMutableArray *array = [[NSMutableArray alloc]init];
Now use addObject: method to add objects. for adding int, bool value create NSNumber object.
It is possible. Just create the array and add the objects you want added.
I want to ask the size of the NSMutable Array can be 2000? If not, is it possible to open an array to store 2000 elements. The elements is the user-defined object. Thank you.
The answer is that an NSMutableArray always starts with a size of zero. If you want it to be so you can do something like this:
NSMutableArray* anArray = [NSMutableArray arrayWithSize: 2000];
[anArray replaceObjectAtIndex: 1999 withObject: foo];
you need to prefill the array with NSNull objects e.g.
#implementation NSArray(MyArrayCategory)
+(NSMutableArray*) arrayWithSize: (NSUInteger) size
{
NSMutableArray* ret = [[NSMutableArray alloc] initWithCapacity: size];
for (size_t i = 0 ; i < size ; i++)
{
[ret addObject: [NSNull null]];
}
return [ret autorelease];
}
#end
Edit: some further clarification:
-initWithCapacity: provides a hint to the run time about how big you think the array might be. The run time is under no obligation to actually allocate that amount of memory straight away.
NSMutableArray* foo = [[NSMutableArray alloc] initWithCapacity: 1000000];
NSLog(#"foo count = %ld", (long) [foo count]);
will log a count of 0.
-initWithCapacity: does not limit the size of an array:
NSMutableArray* foo = [[NSMutableArray alloc] initWithCapacity: 1];
[foo addObject: #"one"];
[foo addObject: #"two"];
doesn't cause an error.
I have an NSMutableArray. It's members eventually become members of an array instance in a class. I want to put the instantiantion of NSMutable into a function and to return an array object. If I can do this, I can make some of my code easier to read. Is this possible?
Here is what I am trying to figure out.
//Definition:
function Objects (float a, float b) {
NSMutableArray *array = [[NSMutableArray alloc] init];
[array addObject:[NSNumber numberWithFloat:a]];
[array addObject:[NSNumber numberWithFloat:b]];
//[release array]; ????????
return array;
}
//Declaration:
Math *operator = [[Math alloc] init];
[operator findSum:Objects(20.0,30.0)];
My code compiles if I instantiate NSMutableArray right before I send the message to the receiver. I know I can have an array argument along with the method. What I have problem seeing is how to use a function and to replace the argument with a function call. Any help is appreciated. I am interested in the concept not in suggestions to replace the findSum method.
Use autorelease to return objects you create in methods/functions.
NSMutableArray* Objects(float a, float b) {
NSMutableArray *array = [[[NSMutableArray alloc] init] autorelease];
// or: [NSMutableArray array];
[array addObject:[NSNumber numberWithFloat:a]];
[array addObject:[NSNumber numberWithFloat:b]];
return array;
}
Or simply:
NSMutableArray* Objects(float a, float b) {
return [NSMutableArray arrayWithObjects:
[NSNumber numberWithFloat:a],
[NSNumber numberWithFloat:b],
nil];
}
I have two classes indexViewController and flashCardQuestionViewController.
In the indexViewController i have table filled with an array.
Now i am getting some data from the database:
-(void)getMultipleChoiceAnswer
{
if(optionid!=nil)
[optionid removeAllObjects];
else
optionid = [[NSMutableArray alloc] init];
if(optionText!=nil)
[optionText removeAllObjects];
else
optionText = [[NSMutableArray alloc] init];
clsDatabase *clsDatabaseObject = [[clsDatabase alloc] init];
sqlite3_stmt *dataRows = [clsDatabaseObject getDataset:"select optionID,OptionText from flashCardMultipleAnswer where questionId=1"];
while(sqlite3_step(dataRows) == SQLITE_ROW)
{
[optionid addObject:[NSNumber numberWithInt:sqlite3_column_int(dataRows,0)]];
[optionText addObject:[NSString stringWithUTF8String:(char *)sqlite3_column_text(dataRows,1)]];
}
sqlite3_finalize(dataRows);
[clsDatabaseObject release];
}
and I am calling this method in the viewDidLoad method of the indexViewController.
Now I have another NSMutableArray in the flashCardQuestionViewController named listNoOfOptionsInQuestion.
I want to fill listNoOfOptionsInQuestion with objects from optionText array in indexViewController.
How can I do this?
There are a number of ways to copy arrays: you can either use -[NSArray copy] to get an immutable copy, or -[NSArray mutableCopy] for a mutable copy. Don't forget that copy adds a reference so you'll need a release or autorelease somewhere (if you're not using GC that is).
Alternatively, you can use -[NSMutableArray addObjectsFromArray:].
Given your example, it looks like you want to do something like this at the end:
[flashCardQuestionViewController setListNoOfOptionsInQuestion:optionText];
And then in FlashCardQuestionViewController, you want something like:
- (void)setListNoOfOptionsInQuestion:(NSArray *)options
{
if (options != listNoOfOptionsInQuestion) {
[listNoOfOptionsInQuestion release];
listNoOfOptionsInQuestion = [options mutableCopy];
}
}
Rahul,
Do you really need to have a completely different copy of the MutableArray in each object. Would it be possible to have both objects point to the same array? For instance:
ClassOne *one = [[ClassOne alloc] init];
ClassTwo *two = [[ClassTwo alloc] init];
// build mutable array mArray
// ...
one.objectArray = mArray;
two.objectArray = mArray;
Or do you need to make changes to the two arrays in different ways? The try this (as suggested by Chris above) :
ClassOne *one = [[ClassOne alloc] init];
ClassTwo *two = [[ClassTwo alloc] init];
// build mutable array mArray
// ...
one.objectArray = mArray;
two.objectArray = [mArray mutableCopy];
again, if this isn't what you need then you'll have to give us a more precise question or problem that we can identify.