I'm working on this assignment I found online (Intermediate App Development Using iOS). I'm stuck on part c and d, don't know exactly what its asking me to do.
I know how to print int (%i) and object (%#), but %# print all data? Any help or suggestion will be appreciated.
Part 6
a) Implement class A with properties a1, a2, and a3 (int, string, int).
b) New objects are automatically initialized to 1, "hello", 1
c) Also provide initializer to any data and constructor (called without alloc) to do the same.
d) Make sure %# object of A will print all data.
Here is what I have done so far:
// classA.h
#import <Foundation/Foundation.h>
#interface ClassA : NSObject
// Part 6a
#property int a1;
#property NSString *a2;
#property int a3;
-(ClassA *) initWithA1: (int) x andA2: (NSString *) s andA3: (int) y;
#end
//classA.m
#import "ClassA.h"
#implementation ClassA
-(ClassA *) initWithA1:(int)x andA2:(NSString *)s andA3:(int)y {
self = [super init];
if (self) {
self.a1 = x;
self.a2 = s;
self.a3 = y;
}
return self;
}
// part 6b
-(ClassA *) init {
if (self = [super init]) {
self.a1 = 0;
self.a2 =#"hello";
self.a3 = 0;
}
return self;
}
#end
In reference to part "b" of your question:
As a general rule, only 1 initializer should be doing the "real" work. This is often referred to as the designated initializer. So, your init method should probably read something like:
- (id) init
{
return [self initWithA1:1 andA2:#"hello" andA3:1];
}
As #orbitor wrote, your class should have one designated initialiser.
So, your init method should probably read something like:
- (id) init
{
return [self initWithA1:1 andA2:#"hello" andA3:1];
}
In order to print all object you should implement custom description method:
- (NSString *) description
{
return [NSString stringWithFormat:#"a1 = %d, a2 = %#, a3 = %d", self.a1, self.a2, self.a3];;
}
According to c:
Class method new just calls alloc and init methods so you should only make sure that you wrote properly all initialisers.
Related
I was playing around with objective C. This is my code for a class I wrote , arithmetic.h:
#import <Foundation/Foundation.h>
#interface arithmetic : NSObject
#property int cur;
-(id)initWithNumber:(int)number;
#end
#implementation arithmetic
#synthesize cur;
- (instancetype)init
{
self = [super init];
if (self) {
NSLog(#"Yo, all works :D ");
}
return self;
}
-(id)initWithNumber:(int)num{
self = [super init];
if(self){
[self setCur:8] ;
}
return self;
}
#end
Note the #property int cur. I was excepting objective c to create a setCur and a getCur method as accessors and mutators for my class. However, when I run this:
arithmetic *test = [[arithmetic alloc] initWithNumber:89];
[test setCur:534];
NSLog("%i",[test getCur ]);
The first two lines work. But the last line says
No visible interface for arithmetic declares the selector 'getCur'
What is the problem ?
It is because when you declare like this in your #implementation:
#synthesize cur;
it will create getter
-(int)cur {
return _cur;
}
and also it will create a setter
-(void)setCur:(int)newCur {
_cur = newCur;
}
In summary, Objective-C getter/setter is having a pattern of propery/setPropery respectively, unlike Java that uses getProperty/setProperty.
And Objective-C getter/setter is accessed via dot(.) notation. For example
int x = obj.cur;
obj.cur = 100;
I'm currently working on a project that's split in two classes, the class 'Array' and the class 'PPCalcVals'. Because other classes, that will be added, will also have to have access the array, I thought it would be the best to write the array class, containing an NSMutableArray and Subclass all the others (beginning with the PPCalcVals class.
So the 'PPCalcVals' class needs to access the elements of the array in the superclass 'Array'.
(Please correct me if this is the wrong approach).
As mentioned the whole program is written and well working in C but to create a GUI and eventually an OSX or IOS application I started to learn OOProgramming with Objecitve C.
Anyways, when I reference the objects in the array of the superclass the only value that gets printed is "null" which is not really what I want.
Here is the code:
main routine:
#import <Foundation/Foundation.h>
#import "Array.h"
#import "PPCalcVals.h"
int main(int argc, const char * argv[])
{
#autoreleasepool
{
Array *prices = [[Array alloc]initWithName:#0];
PPCalcVals *myVals = [[PPCalcVals alloc]init];
[prices addValue:#12];
[prices addValue:#13];
[prices addValue:#14];
[prices addValue:#15];
[prices addValue:#15];
[prices print];
[myVals print];
}
return 0;
}
array.h file:
#import <Foundation/Foundation.h>
#interface Array : NSObject
{
NSMutableArray *prices;
}
-(id) initWithName: (NSNumber *) values;
-(void) addValue: (NSNumber *) value;
-(void) print;
-(NSMutableArray *) prices;
#end
array.m
#import "Array.h"
#implementation Array
-(id) initWithName:(NSNumber *)values
{
self = [super init];
if(self)
{
prices = [NSMutableArray array];
}
return self;
}
-(void) addValue: (NSNumber *) value
{
[prices addObject:value];
}
-(void) print
{
NSLog(#"%#",prices);
}
-(NSMutableArray *)prices
{
return prices;
}
#end
PPCalcVals.h:
#import "Array.h"
#interface PPCalcVals : Array
#property id high,low,open,close;
-(void) setHigh:(NSMutableArray *)h setLow:(NSMutableArray *)l; //set high and low
-(void) setOpen:(NSMutableArray *)o setClose:(NSMutableArray *)c; //set open and close
-(void) sort; //sort array
-(void) print; //debugging tool
#end
PPCalcVals.m:
#import "PPCalcVals.h"
#implementation PPCalcVals
#synthesize high,low,open,close;
-(void) setOpen:(NSMutableArray *)o setClose:(NSMutableArray *)c
{
o = prices[0];
c = prices[2];
open = o;
close = c;
}
-(void) sort;
{
[prices sortedArrayUsingComparator:^(NSString *str1, NSString *str2) {
return [str1 compare:str2 options:NSNumericSearch];
}];
}
-(void) setHigh:(NSMutableArray *)h setLow:(NSMutableArray *)
{
h = prices[0];
l = prices[2];
high = h;
low = l;
}
-(void) print
{
NSLog(#"open: %#",open);
NSLog(#"close: %#",close);
NSLog(#"high: %#",high);
NSLog(#"low: %#",low);
}
#end
The running program outputs only:
2013-08-05 10:21:08.546 prog1[1314:303] (
12,
13,
14,
15,
15
)
open: (null)
close: (null)
high: (null)
low: (null)
I realize that this is probably a really basic question but I would appreciate your help a lot and I already thank you if you read until this point ;)
You have created two distinct, completely unrelated objects prices and myVals:
Array *prices = [[Array alloc]initWithName:#0];
PPCalcVals *myVals = [[PPCalcVals alloc]init];
What you probably meant is to create a PPCalcVals object (which inherits
all methods from the superclass Array):
PPCalcVals *prices = [[PPCalcVals alloc]init];
[prices addValue:#12]; // invokes `addValue` method from superclass "Array"
// ...
[prices print]; // invokes `print` method from "PPCalcVals"
You also have to implement init in the PPCalcVals class in such a way
that it calls the "designated initializer" initWithName in the superclass.
I have one question. Where did you make calls for the functions
-(void) setHigh:(NSMutableArray *)h setLow:(NSMutableArray *)l;
-(void) setOpen:(NSMutableArray *)o setClose:(NSMutableArray *)c;
Because all I can see is that these functions are not called. So the properties high, low, open & close are not yet assigned and thus they return Null.
Also may I know the reason why are you overriding the parameters inside above mentioned functions?
o = prices[0];
c = prices[2];
and
h = prices[0];
l = prices[2];
I'm new in Objective C and stuck on this problem already 5 days)) What i have to do is write implementation for simple task about city and metropolis. I have class City with properties and class metropolis that has an global array which adds city object through createCity method. I have implemented this task but this arrays returns nothing.
Can anybody help me?
Here is part of the task:
1. Write a “City” class, which inherits from NSObject. Your class should contain the following:
Variables:
name, age, population.
Instance methods:
setName:age:population (single method) which set city’s name, age and population. getName, getAge, getPopulation which return city’s name, age and population, respectfully.
nextDay which adds a random number to city’s population, then subtracts a random number from city’s population. Figure out a way to generate random numbers yourself.
2. Create an instance of City class, set its name, age and population as you want.
3. Write a for-‐loop (if in doubt how to do it – google or use Xcode’s help system) for 10 steps. Each step send ‘nextDay’ message to your object and print out the population.
4. Write a “Metropolis” class. It should contain the following:
Variable:
array of 10 cities.
Instance method:
createCity:atIndex:withPopulation: (single method) which creates a city with first parameter being a name at index (from the second parameter) and sets its population to that of third parameter. So, you should be able to do this:
[myMetropolis createCity: #”Almaty” atIndex: 2 withPopulation: 1500000]
5. Create an instance of Metropolis class and create all 10 cities.
Here is my implementation:
City.h
#import <Foundation/Foundation.h>
#interface City : NSObject
{
NSString* name;
int age;
int population;
}
-(void)setName: (NSString*)n age: (int)a population: (int)p;
-(NSString*)getName;
-(int)getAge;
-(int)getPopulation;
-(void)nextDay;
#end
City.m
#import "City.h"
#implementation City
-(void)setName:(NSString*)n age:(int)a population:(int)p
{
name = n;
age = a;
population = p;
}
-(NSString*)getName
{
return name;
}
-(int)getAge
{
return age;
}
-(int)getPopulation
{
return population;
}
-(void)nextDay
{
int r = arc4random() % 100;
int r2 = arc4random() % 100;
population = population + r;
population = population - r2;
}
#end
Metropolis.h
#import <Foundation/Foundation.h>
#import "City.h"
#interface Metropolis : NSObject{
NSMutableArray* myArray;
}
-(void)createCity: (NSString*)n atIndex: (int)a withPopulation: (int)p;
-(NSMutableArray*) getArray;
#end
Metropolis.m
#import "Metropolis.h"
#import "City.h"
#implementation Metropolis
NSMutableArray* myArray = nil;
- (void)initialize {
myArray = [[NSMutableArray alloc]initWithCapacity:10];
}
-(void)createCity:(NSString*)n atIndex:(int)a withPopulation:(int)p
{
City* newCity = [[City alloc]init];
[newCity setName:n age:0 population:p];
[myArray insertObject:newCity atIndex:a];
}
-(NSMutableArray*)getArray
{
return myArray;
}
#end
main.m
#import <Foundation/Foundation.h>
#import "City.h"
#import "Metropolis.h"
int main(int argc, const char * argv[])
{
#autoreleasepool {
Metropolis* myMetropolis = [[Metropolis alloc]init];
[myMetropolis createCity:#"Aktobe" atIndex:0 withPopulation:15];
[Metropolis initialize];
NSMutableArray* c = [[NSMutableArray alloc]init];
c = [myMetropolis getArray];
NSLog(#"%#", [[c objectAtIndex:0] getName]);
}
return 0;
}
The method for initialization is -(void)init; this method should be overwritten in your implementation of Metropolis.
You are calling - (void)initialize; which is wrong in this case.
So, simply change - (void)initialize { to -(void)init { in your implementation of Metropolis and delete the line: [Metropolis initialize]; in main.
After the comment below the proper init method should be:
-(id) init {
self = [super init];
if (self) {
myArray = [[NSMutableArray alloc]initWithCapacity:10];
}
return self;
}
I've rewritten my answer to make it more complete, and to incorporate some of the other ideas generated in the other answers, especially #Hannes Sverrisson
The easy way to fix your issue is to call initialize BEFORE createCity (otherwise your trying to add objects to a nil array) and to also make sure you're not calling initialize from a static context. i.e. change [Metropolis initialize]; to [myMetropolis initialize];
The better way, and by better I mean more consistent with typical objective-c design, you should override the instance method init. This is done in the Metropolis implementation and replaces your initialize method.
-(id) init {
self = [super init];
if (self) {
myArray = [[NSMutableArray alloc]initWithCapacity:10];
}
return self;
}
or to make it more fun, create a new init method that takes the number of cities as a parameter.
-(id) initWithNumberOfCities:(NSInteger)numCities {
self = [super init];
if (self) {
myArray = [[NSMutableArray alloc]initWithCapacity:numCities];
}
return self;
}
Then in your main method, remove the call to [Metropolis initialize]. The reason for this is when you say:
Metropolis* myMetropolis = [[Metropolis alloc]init];
or
Metropolis* myMetropolis = [[Metropolis alloc]initWithNumberOfCities:10];
the init method is being called inline after the allocation takes place.
You don't need to write getters or create backing instance variables. You can use Objective-C 2.0's #property syntax.
#property (strong) NSString *name;
#property (assign) NSInteger age;
#property (assign) NSInteger population;
- (void)setName:(NSString*)name age:(NSInteger)age population:(NSInteger)population;
- (void)nextDay;
Then you access the properties using self.name, self.age, self.population or if you need to access the backing variable itself, _name, _age, _population.
Please have a look on following code :------- .h
#interface BankAccount : NSObject<NSCopying>
{
double accountBalance;
long accountNumber;
NSString *CustomerName;
NSString *AccountType;
}
-(void) setAccount: (long) y andBalance: (double) x;
-(void) setCustomerName: (NSString*) name andAccountType: (NSString*) type;
-(id)copyWithZone:(NSZone *)zone;
#end
#interface Savings : BankAccount
{
int number;
NSString *Offer;
}
-(void) setSavingNumber: (uint8_t) num andOffer: (NSString*) offer;
-(id)copyWithZone:(NSZone *)zone;
#end
---------- .m
#implementation BankAccount
-(void) setAccount: (long) y andBalance: (double) x
{
accountNumber = y;
accountBalance = x;
}
-(void) setCustomerName: (NSString*) name andAccountType: (NSString*) type
{
CustomerName = name;
AccountType = type;
}
-(id)copyWithZone:(NSZone *)zone
{
BankAccount *accountCopy = [[BankAccount allocWithZone: zone] init];
[accountCopy setAccount: accountNumber andBalance: accountBalance];
[accountCopy setCustomerName:CustomerName andAccountType:AccountType];
return accountCopy;
}
#end
#implementation Savings
-(void) setSavingNumber: (uint8_t) num andOffer: (NSString*) offer
{
number = num;
Offer = offer;
}
-(id)copyWithZone:(NSZone *)zone
{
Savings * clone = [super copyWithZone:zone];
[clone setSavingNumber:number andOffer:Offer];************** error *********
return clone;
}
#end
When run this code::::::
Savings* account1;
Savings* account2;
account1 = [[Savings alloc] init];
[account1 setAccount:10 andBalance:1000.10];
[account1 setCustomerName:[NSString stringWithFormat:#"%#",#"Deepak"] andAccountType:[NSString stringWithFormat:#"%#",#"Savings"]];
[account1 setSavingNumber:2001 andOffer:#"Bad"];
account2 = [account1 copy];
#
i dont know what is wrong with the code please help me. thanks in advance.
Thanks
Deepak
Your base copyWithZone: method should look like this:
-(id)copyWithZone:(NSZone *)zone {
// change this line to use [self class]
BaseClass *base = [[[self class] allocWithZone:zone] init];
// copy base members:
// ...
return base;
}
Your derived copyWithZone: methods should look like this:
-(id)copyWithZone:(NSZone *)zone {
DerivedClass *derived = [super copyWithZone:zone];
// copy derived members:
// ...
return derived;
}
Also make sure sure you are making deep copies of strong references and shallow copies of weak references. Thus to for example copy members of type NSString and NSArray (each one with strongly referenced members and one with weak) do:
derived.strongString = [[strongString copyWithZone:zone] autorelease];
derived.weakString = weakString;
derived.strArrWStrVals = [[strArrWStrVals copyWithZone:zone] autorelease];
derived.strArrWWeakVals = [[[NSArray allocWithZone:zone]
initWithArray:strArrWWeakVals] autorelease];
derived.weakArray = weakArray;
(Usually weak members are also assigned/retained and strong variables are copied.)
Take note that because of this you should not use initWithMyself: type methods to copy data.
Ok first, your test code is bad because you set a saving number of 2001 in an 8 bit integer. Second, your code does not run because you're trying to call setSavingNumber:andOffer: on a BankAccount instead of an Saving object so it can't find the selector for this method at run time. Thanks David for pointing that out.
When implementing BankAccount::copyWithZone, you used the alloc-init and you returned the object which is fine. When implementing Savings::copyWithZone, you call super copyWithZone. What you get is an object of type BankAccount so you cannot use setSavingNumber:andOffer: on it. Since you used the alloc-init in the base class, you should also use the alloc-init and setMethods in the Savings class.
To avoid duplicating code, I'd recomment implementing an initWithBankAccount in BankAccount and the same in Savings.
Then in the copyWithZone, you'd have
return [[BankAccount allocWithZone:zone] initWithBankAccount:self];
and
return [[Savings allocWithZone:zone] initWithSavings:self];
Although you must make sure that in initWithSavings you call either
self = [super initWithBankAccount:savings];
or you call straight init and you copy the base member initialization.
Have a look at Implementing object copy from Memory management programming guide.
thing.h
#interface Thing : NSObject
{
float stuff[30];
}
#property float stuff;
#end
thing.m
#implementation Thing
#synthesize stuff;
#end
I get error: type of property 'stuff' does not match type of ivar 'stuff'
I don't want to use an NSArray because I'd have to make the floats into NSNumbers (right?) and that's a pain to do math with.
Update: I've noticed similar answers had guesses and trial answers. While I appreciate the attempts by non-Objective-C folks, I'm hoping for a definitive answer whether it's possible or not.
OK, I have compiled up the following code at it works as expected.
FloatHolder.h
#interface FloatHolder : NSObject {
int _count;
float* _values;
}
- (id) initWithCount:(int)count;
// possibly look into this for making access shorter
// http://vgable.com/blog/2009/05/15/concise-nsdictionary-and-nsarray-lookup/
- (float)getValueAtIndex:(int)index;
- (void)setValue:(float)value atIndex:(int)index;
#property(readonly) int count;
#property(readonly) float* values; // allows direct unsafe access to the values
#end
FloatHolder.m
#import "FloatHolder.h"
#implementation FloatHolder
#synthesize count = _count;
#synthesize values = _values;
- (id) initWithCount:(int)count {
self = [super init];
if (self != nil) {
_count = count;
_values = malloc(sizeof(float)*count);
}
return self;
}
- (void) dealloc
{
free(_values);
[super dealloc];
}
- (float)getValueAtIndex:(int)index {
if(index<0 || index>=_count) {
#throw [NSException exceptionWithName: #"Exception" reason: #"Index out of bounds" userInfo: nil];
}
return _values[index];
}
- (void)setValue:(float)value atIndex:(int)index {
if(index<0 || index>=_count) {
#throw [NSException exceptionWithName: #"Exception" reason: #"Index out of bounds" userInfo: nil];
}
_values[index] = value;
}
#end
then in your other application code you can do something like the following:
** FloatTestCode.h **
#import <Cocoa/Cocoa.h>
#import "FloatHolder.h"
#interface FloatTestCode : NSObject {
FloatHolder* holder;
}
- (void) doIt:(id)sender;
#end
** FloatTestCode.m **
#import "FloatTestCode.h"
#implementation FloatTestCode
- (id) init
{
self = [super init];
if (self != nil) {
holder = [[[FloatHolder alloc] initWithCount: 10] retain];
}
return self;
}
- (void) dealloc
{
[holder release];
[super dealloc];
}
- (void) doIt:(id)sender {
holder.values[1] = 10;
}
The type of the property must match the type of the instance variable it will be stored in, so you could do something like
#interface Thing : NSObject
{
float stuff[30];
}
#property float[30] stuff;
#end
and it should work. I wouldn't recommend it though.
I'm guessing you're looking for something like indexed properties from Delphi. The closest you'll get is something like the following.
#interface Thing : NSObject
{
float stuff[30];
}
- (void) setStuff:(float)value atIndex:(int)index;
- (float) getStuffAtIndex:(int)index;
#end
You can't do it the way you want to do it. You can jump through some hoops and get something similar, e.g. using Daniel's solution, but it's not quite the same thing. The reason you can't do it is that arrays are not lvalues in C. An lvalue is something that can appear on the left-hand side of an assignment. The following code is invalid C:
float stuff1[30], stuff2[30];
stuff1 = stuff2; // ERROR: arrays are not lvalues
As a consequence, you can't declare properties whose types are not lvalues.
Daniel's FloatHolder answer has a major bug (edit: he's now fixed it). It only allocates memory for one float and not for the whole array.
The line:
_values = malloc(sizeof(float));
Should be:
_values = malloc(sizeof(float) * count);
Otherwise it seems to be a good answer. Sorry couldn't work out how to reply directly. (edit: I didn't have the necessary privilege on stackoverflow then.)
Even if you could get that to compile, it wouldn't behave well. 'stuff' would return a float*, and the client would have no idea how long the array way; 'setStuff:' would just change the pointer, and you'd either be pointing to stack-allocated data that would vanish out from under you or heap-allocated data that would leak because it wouldn't know to free it.
I'm not well-versed in Objective-C 2.0, but I'm guessing that the issue might be caused by the fact that a C array is essentially just a pointer to the first element of the array, meaning that the type of float stuff[30] is actually float *, not merely a float.