I am working on getting a list of songs to sort by artist. I have my code working and can print the songs and artists. Now I want to make it sort and print the list by artist. This is my first attempt at sorting and I know I have to be missing something simple here. I get -- Expected ')'-- and -- use of undeclared identifier 'listSongs' -- This is all in my #implementation file.
Any help is appreciated thank you in advance.
Here is my interface section
#interface Library : NSObject
#property (nonatomic, strong) NSMutableArray *list;
-(id) initList;
-(void) addSong: (Song *) song;
-(void) listSongs;
#end
This is my implementation section
#import "Library.h"
#implementation Library
#synthesize list;
-(id) initList
{
self = [super init];
if (self){
list = [NSMutableArray array];
}
return self;
}
-(id) init
{
return [self initList];
}
-(void) addSong:(Song *)song
{
[list addObject: song];
}
-(void) listSongs
{
NSLog(#"The list of my songs");
NSSortDescriptor *sorter;
sorter = [[[NSSortDescriptor alloc] initWithKey:#"artist" ascending: YES]
NSArray *sortDescriptors = [NSArray arrayWithObjects:sorter]; **// ** Expected ')'**
[listSongs sortUsingDescriptors:sortDescriptors]; //**use of undeclared identifier 'listSongs'
for (Song *song in list)
NSLog(#"%-20s by %s", [song.Title UTF8String], [song.Artist UTF8String]);
}
You should use NSArray *sortedArray = [listSongs arraySortedUsingDescriptors:sortDescriptors];
Basically this method returns a sorted array, it is called on an unsorted array and is given an array of sort descriptors.
As I understand from your code, what you're trying to do is to sort list which is declared property.
You need to replace this line
[listSongs sortUsingDescriptors:sortDescriptors];
With
self.list = [self.list sortUsingDescriptors:sortDescriptors];
Related
UPDATE: Now working (added fixes as suggested - Thanks!)
I've been trying to clone an NSDictionary of employee info. The main NSDictionary is created in a different class and passed along in prepareForSegue. I want to be able to create a mutable copy of that NSDictionary in another class which can then update the employee info and send it off to another class for processing so I still have the original unchanged dataset to work with at a later time. I've found a few different examples on Stack, but nothing I could get working. When I break on the btn_click method and examine the local pp object after the ..objectForKey call, pp is still nil. What have I done wrong here?
obj_person.h
#import <Foundation/Foundation.h>
#interface obj_person : NSObject
#property (strong,nonatomic) NSString *personID;
#property (strong, nonatomic) NSString *personName;
#property (strong, nonatomic) NSString *personTitle;
#end
obj_person.m
#import "obj_person.h"
#implementation obj_person
#synthesize personID = _personID;
#synthesize personName = _personName;
#synthesize personTitle = _personTitle;
#end
viewcontroller.m
#import "ViewController.h"
#import "obj_person.h"
#interface ViewController ()
#end
#implementation ViewController
int mCounter = 1;
NSMutableDictionary *mCopy;
NSMutableDictionary *mNsd;
- (void)viewDidLoad
{
[super viewDidLoad];
NSArray *arnames = [[NSArray alloc] initWithObjects:#"mary", #"jane", #"stan", #"cartman", nil];
NSArray *arkeys = [[NSArray alloc] initWithObjects:[NSNumber numberWithInt:1], [NSNumber numberWithInt:2],[NSNumber numberWithInt:3], [NSNumber numberWithInt:4], nil];
mNsd = [[NSMutableDictionary alloc] initWithCapacity:[arnames count]];
int i = 0;
for (NSString *name in arnames)
{
obj_person *p = [[obj_person alloc] init];
p.personID = [arkeys objectAtIndex:i];
p.personName = name;
[mNsd setObject:p forKey:p.personID];
i++;
}
mCopy = [mNsd mutableCopy];
}
- (IBAction)btn_click:(id)sender
{
NSLog (#"%d original items", [mNsd count]);
obj_person *pp = [mCopy objectForKey:[NSNumber numberWithInt:mCounter]];
NSLog(#"%#", pp.personName);
pp.personName = #"Gerald";
if (++mCounter > [mCopy count])
mCounter = 1;
}
#end
Don't define:
NSMutableDictionary *mCopy;
NSMutableDictionary *mNsd;
Outside of the #interface and #implementation. They should be instance variables, so define instance variables or use properties to define them.
It's a good job you don't use n from:
for (NSArray *n in arnames)
because it isn't an NSArray, it's an NSString. You should fix that and you should probably both name it better than n and use it.
This:
obj_person *pp = [mCopy objectForKey:[NSNumber numberWithInt:1]];
fails because the key you originally stored with is an NSString instance and the thing you are using to try to get the data out is an NSNumber instance (so they can never match).
You might try:
mCopy = [mNsd mutableCopy];
[mCopy retain]
One theory is that the mutableCopy returns is an autoreleased object and it's being killed off before the btn_click function fires. According to this post: Retain/release of returned objects, mutableCopy should not be autoreleasing the array, but bugs do happen.
Else, maybe try iterating through with a for-loop instead.
int cnt = [arnames count];
for(int i=0; i<cnt; i++)
...
This is code from an addition calculator that does operations by entering the two operands first and then the operation; like "5 enter 2 enter +" would result in "7". When the user taps on a number a double will be sent to pushOperand: When a user taps on the addition button the string #"+" will be sent like to performOperation:. My question is what is the point of making those copies in program and runProgram: if they're all shallow copies and their elements all end up pointing to the same elements of NSNumber and NSString objects as _programStack, program, and stack?
#import <Foundation/Foundation.h>
#interface CalculatorBrain : NSObject
#property (nonatomic, readonly) id program;
+(double)runProgram:(id)program;
-(double)performOperation:(NSString *)operation;
#end
#import "CalculatorBrain.h"
#interface CalculatorBrain ()
#property (nonatomic, strong) NSMutableArray *programStack;
#end
#implementation CalculatorBrain
#synthesize programStack = _programStack;
-(NSMutableArray *) programStack {
if (!_programStack)
_programStack = [[NSMutableArray alloc] init];
return _programStack;
}
-(void)pushOperand:(double)operand {
[self.programStack addObject: [NSNumber numberWithDouble: operand]];
}
-(double)performOperation:(NSString *)operation {
[self.programStack addObject: operation];
double result = [CalculatorBrain runProgram: self.program];
return result;
}
-(id)program {
return [self.programStack copy];
}
+(double)runProgram:(id)program {
NSMutableArray *stack;
if ([program isKindOfClass: [NSArray class]])
stack = [program mutableCopy];
return [self popOperandOffProgramStack: stack];
}
+(double)popOperandOffProgramStack:(NSMutableArray *)stack {
double result = 0;
id topOfStack = [stack lastObject];
if (topOfStack)
[stack removeLastObject];
if ([topOfStack isMemberOfClass: [NSNumber class]])
result = [topOfStack doubleValue];
if ([topOfStack isKindOfClass: [NSString class]]) {
NSString *operation = topOfStack;
if ([operation isEqualToString: #"+"]) {
result = [self popOperandOffProgramStack: stack] + [self popOperandOffProgramStack: stack];
}
return result;
}
#end
NSNumber and NSString are immutable so making a shallow copy of a collection of objects that can't changee is safe.
In program it is important to return a copy of programStack rather than the the actual mutable array. This is because programStack is a private internal property declared in a class extension so it is not externally visible. If you returned programStack directly an external user could change it since it is an NSMutableArray. The program method returns an NSArray since copies of mutable objects are immutable, which has the right semantics. You want to give the external user a snapshot of the programStack array, not access to your class internals.
In runProgram the situation is different. The external user passes CalculatorBrain an NSArray to process and the class' internal logic requires that the stack have elements popped off the array as it is processed. Thus you need to make a mutableCopy so that it can be mutated for processing.
I want to use a variable-sized multi-dimensional array in my app to save data. The data structure I want to use is as below, the first element in each row is followed by corresponding multiple values.
array = { {a, a_val1, a_val2, a_val3}.
{b, b_val1},
{c, c_val1, c_val2, c_val3, c_val4, c_val5}
}
Any idea how I can implement in objective-c?
use NSMutableArray like so
NSMutableArray *curRow; /* use to access the row while loading with objects */
NSMutableArray *array = [[NSMutableArray alloc] init]; /* your main multidim array */
curRow = [NSMutableArray array];
[curRow addObject:/* what you want here */];
[curRow addObject:/* what you want here */];
[curRow addObject:/* what you want here */];
[array addObject:curRow]; /* first row is added */
/* rinse and repeat */
curRow = [NSMutableArray array];
[curRow addObject:/* what you want here */];
[curRow addObject:/* what you want here */];
[curRow addObject:/* what you want here */];
[array addObject:curRow];
use NSMutableArray
Below is the example for your understanding ...
NSMutableArray * multiArray = [[NSMutableArray alloc] initWithCapacity:5];
[multiArray addObject:[NSArray arrayWithObjects:a,a_val1,a_val2]];
[multiArray addObject:[NSArray arrayWithObjects:a,a_val1,a_val2,a_val3,a_val4]];
[multiArray addObject:[NSArray arrayWithObjects:a,a_val1,a_val5]];
[multiArray addObject:[NSArray arrayWithObjects:a,a_val1,a_val2,a_val3,a_val4,a_val5,a_val6]];
And Don't forget to release to multiArray array because we have alloced it ...
Objective-C does not have a real 2 dimensional array type but you can implement it with the
following codes..
in your header file --- yourheader.h
#import <Foundation/Foundation.h>
#interface yourheader : NSObject{
NSMutableDictionary* DictionaryArrayType;
NSMutableArray* MultiArrayType;
NSArray* CaptionTitle;
NSArray* ObjectValue;
}
#property (strong, nonatomic) NSMutableDictionary* DictionaryArrayType;
#property (strong, nonatomic) NSArray* CaptionTitle;
#property (strong, nonatomic) NSArray* ObjectValue;
#property (strong, nonatomic) NSMutableArray* MultiArrayType;
-(id) AddArrayObjects:(NSString*)_Name : (NSString*)_Surname :(NSString*)_Age;
-(id) AddArrayDictionaryObject:(NSArray*)_ArrayObject : (NSArray*)_ArrayKey;
-(id) AddMultiArrayType:(id)_ArrayObject;
-(void) ShowMultiArrayType:(id)_ArrayObject;
#end
Now add to your objective-c file ---- objective-c.m
#import "yourheader.h"
#implimentation yourheader
#synthesize DictionaryArrayType;
#synthesize CaptionTitle;
#synthesize ObjectValue;
#synthesize MultiArrayType;
-(id)init {
if(self = [super init]){
NSString* const NAME = #"NAME";
NSString* const SURNAME = #"SURNAME";
NSString* const AGE = #"AGE";
//Adding fixed content to CaptionTitle Array
[self setCaptionTitle:[NSArray arrayWithObjects:NAME, SURNAME, AGE, nil]];
//add values to ObjectValue array
[self AddArrayObjects:#"Bob" :#"Obi" :#"200"];
//add values to dictionary
[self AddDictionaryArrayType:ObjectValue :CaptionTitle];
//Add to the Multi dimensional array [][]
[self AddMultiArrayType:DictionaryArrayType];
//add the second row values to ObjectValue array
[self AddArrayObjects:#"Barack" :#"Obama" :#"50"];
//add values to dictionary
[self AddDictionaryArrayType:ObjectValue :CaptionTitle];
//Add to the Multi dimensional array [][]
[self AddMultiArrayType:DictionaryArrayType];
//display the 2d Array
[self ShowMultiArrayType:MultiArrayType];
}
return self;
}
-(id)AddArrayObjects:(NSString *)_name :(NSString *)_surname :(NSString *)_age {
//Set the Array Objects;
[self setObjectValue:[NSArray arrayWithObjects:_name, _surname, _age, nil]];
return self;
}
-(id)AddDictionaryArrayType:(NSArray *)_ArrayObject :(NSArray*)_ArrayKey {
if(!DictionaryArrayType) {
//initialize disctionary
[self setDictionaryArrayType:[NSMutableDictionary dictionary]];
}
//add array obeject and Fixed Key decleared in CaptionTitle array
DictionaryArrayType = [NSMutableDictionary dictionaryWithObjects:_ArrayObject forKeys:_ArrayKey];
return self;
}
-(id) AddMultiArrayType:(id)_ArrayObject {
if(!MultiArrayType) {
[self setMultiArrayType:[NSMutableArray array]];
}
[MultiArrayType addObject:_ArrayObject];
return self;
}
-(void)ShowMultiArrayType:_ArrayObject {
for(id objects in _ArrayObject ) {
for(id key in objects) {
NSLog(#"%# key = : object = %#", key, [objects objectForKey:key]);
}
}
}
#end;
To finish add this to your appdelegate.m file inside the app
yourclassname* _yourclasspointer = [[yourclassname alloc] init];
[_youclasspointer ShowMultiArrayType:[_yourclasspointer MultiArrayType]];
You should see it in you console.
How can I call a method with multiple params like below with performSelectorInBackground?
Sample method:
-(void) reloadPage:(NSInteger)pageIndex firstCase:(BOOL)firstCase;
The problem is that performSelectorInBackground:withObject: takes only one object argument. One way to get around this limitation is to pass a dictionary (or array) of arguments to a "wrapper" method that deconstructs the arguments and calls your actual method:
- (void)callingMethod {
NSDictionary * args = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInteger:pageIndex], #"pageIndex",
[NSNumber numberWithBool:firstCase], #"firstCase",
nil];
[self performSelectorInBackground:#selector(reloadPageWrapper:)
withObject:args];
}
- (void)reloadPageWrapper:(NSDictionary *)args {
[self reloadPage:[[args objectForKey:#"pageIndex"] integerValue]
firstCase:[[args objectForKey:#"firstCase"] boolValue]];
}
- (void)reloadPage:(NSInteger)pageIndex firstCase:(BOOL)firstCase {
// Your code here...
}
This way you're only passing a "single" argument to the backgrounding call, but that method can construct the multiple arguments you need for the real call (which will take place on the same backgrounded thread).
I've just found this question and wasn't happy with any of the answers. In my opinion neither make good use of the tools available, and passing around arbitrary information in arrays and dictionaries generally worries me.
So, I went and wrote a small NSObject category that will invoke an arbitrary selector with a variable number of arguments:
Category Header
#interface NSObject (NxAdditions)
-(void)performSelectorInBackground:(SEL)selector withObjects:(id)object, ... NS_REQUIRES_NIL_TERMINATION;
#end
Category Implementation
#implementation NSObject (NxAdditions)
-(void)performSelectorInBackground:(SEL)selector withObjects:(id)object, ...
{
NSMethodSignature *signature = [self methodSignatureForSelector:selector];
// Setup the invocation
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
invocation.target = self;
invocation.selector = selector;
// Associate the arguments
va_list objects;
va_start(objects, object);
unsigned int objectCounter = 2;
for (id obj = object; obj != nil; obj = va_arg(objects, id))
{
[invocation setArgument:&obj atIndex:objectCounter++];
}
va_end(objects);
// Make sure to invoke on a background queue
NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithInvocation:invocation];
NSOperationQueue *backgroundQueue = [[NSOperationQueue alloc] init];
[backgroundQueue addOperation:operation];
}
#end
Usage
-(void)backgroundMethodWithAString:(NSString *)someString array:(NSArray *)array andDictionary:(NSDictionary *)dict
{
NSLog(#"String: %#", someString);
NSLog(#"Array: %#", array);
NSLog(#"Dict: %#", dict);
}
-(void)someOtherMethod
{
NSString *str = #"Hello world";
NSArray *arr = #[#(1337), #(42)];
NSDictionary *dict = #{#"site" : #"Stack Overflow",
#"url" : [NSURL URLWithString:#"http://stackoverflow.com"]};
[self performSelectorInBackground:#selector(backgroundMethodWithAString:array:andDictionary:)
withObjects:str, arr, dict, nil];
}
Well, I have used this:
[self performSelectorInBackground:#selector(reloadPage:)
withObject:[NSArray arrayWithObjects:pageIndex,firstCase,nil] ];
for this:
- (void) reloadPage: (NSArray *) args {
NSString *pageIndex = [args objectAtIndex:0];
NSString *firstCase = [args objectAtIndex:1];
}
with performSelectorInBackground you can only pass one argument, so make a custom object for this method to hold your data, itll be more concise than an ambiguous dictionary or array. The benefit of this is you can pass the same object around when done containing several return properties.
#import <Foundation/Foundation.h>
#interface ObjectToPassToMethod : NSObject
#property (nonatomic, strong) NSString *inputValue1;
#property (nonatomic, strong) NSArray *inputArray;
#property (nonatomic) NSInteger returnValue1;
#property (nonatomic) NSInteger returnValue2;
#end
and pass that object to your method:
ObjectToPassToMethod *obj = [[ObjectToPassToMethod alloc] init];
obj.inputArray = #[];
obj.inputValue1 = #"value";
[self performSelectorInBackground:#selector(backgroundMethod:) withObject:obj];
-(void)backgroundMethod:(ObjectToPassToMethod*)obj
{
obj.returnValue1 = 3;
obj.returnValue2 = 90;
}
make sure to clean up the object when done to prevent memory leaks
Given a basic key/value array, I'm wanting to store two sorted arrays based on the original array: one array will be sorted by name, and the other by age.
The arrays seem to be sorting correctly when I output them to the log; however, when I try to access them elsewhere in the code, I'm receiving a EXC_BAD_ACCESS error.
Here's what I have so far:
// MyController.h
#interface MyController : UIViewController {
NSMutableArray *originalArray;
NSMutableArray *nameArray;
NSMutableArray *ageArray;
}
#property (nonatomic, retain) NSMutableArray *originalArray;
#property (nonatomic, retain) NSMutableArray *nameArray;
#property (nonatomic, retain) NSMutableArray *ageArray;
-(void)someRandomMethod;
#end
// MyController.m
#import "MyController.h"
#implementation MyController
#synthesize originalArray;
#synthesize nameArray;
#synthesize ageArray;
-(void)viewDidLoad {
// originalArray = (
// {
// "name" = "Sally";
// "age" = 18;
// },
// {
// "name" = "Chad";
// "age" = 26;
// },
// {
// "name" = "Carla";
// "age" = 24;
// },
// )
// sort by name
NSSortDescriptor *sortByNameDescriptor;
sortByNameDescriptor = [[[NSSortDescriptor alloc]
initWithKey:#"name"
ascending:NO] autorelease];
NSArray *sortByNameDescriptors = [NSArray arrayWithObject:sortByNameDescriptor];
nameArray = [originalArray sortedArrayUsingDescriptors:sortByNameDescriptors];
// sort by age
NSSortDescriptor *sortByAgeDescriptor;
sortByAgeDescriptor = [[[NSSortDescriptor alloc]
initWithKey:#"age"
ascending:NO] autorelease];
NSArray *sortAgeDescriptors = [NSArray arrayWithObject:sortByAgeDescriptor];
ageArray = [originalArray sortedArrayUsingDescriptors:sortByAgeDescriptors];
[super viewDidLoad];
}
-(void)someRandomMethod {
// whenever I try to access the sorted arrays, I receive the EXC_BAD_ACCESS error
[[nameArray objectAtIndex:0] valueForKey:#"name"];
[[ageArray objectAtIndex:0] valueForKey:#"age"];
}
-(void)viewDidUnload {
self.originalArray = nil;
self.nameArray = nil;
self.ageArray = nil;
[super viewDidUnload];
}
- (void)dealloc {
[originalArray release];
[nameArray release];
[ageArray release];
[super dealloc];
}
#end
Any ideas?
UPDATE: Thanks to #robin, by changing the code above to the code below, everything works great:
// sort by name
NSSortDescriptor *sortByNameDescriptor;
sortByNameDescriptor = [[[NSSortDescriptor alloc]
initWithKey:#"name"
ascending:NO] autorelease];
NSArray *sortByNameDescriptors = [NSArray arrayWithObject:sortByNameDescriptor];
nameArray = [[NSMutableArray alloc] initWithArray:[originalArray sortedArrayUsingDescriptors:sortByNameDescriptors]];
// sort by age
NSSortDescriptor *sortByAgeDescriptor;
sortByAgeDescriptor = [[[NSSortDescriptor alloc]
initWithKey:#"age"
ascending:NO] autorelease];
NSArray *sortAgeDescriptors = [NSArray arrayWithObject:sortByAgeDescriptor];
ageArray = [[NSMutableArray alloc] initWithArray:[originalArray sortedArrayUsingDescriptors:sortByAgeDescriptors]];
I dont think you know about this or not but when ever you create an object like string or array or dictionary, with init methods then the retain count gets incremented by 1
and if you create them like this
NSArray *anarray = [NSArray arrayWithArray:temp];
this will create an autorelease objects that will be released automatically after sometime.
So my advice don't use this type of code if you want to use the objects in more than 1 function. Always use init methods first to get the work done.
and if you are sure that the objects are not needed for the rest of the program than release them using release methode.