What I want to do seems pretty simple, but I can&#39;t find any answers on the web. I have an `NSMutableArray` of objects, and let&#39;s say they are &#39;Person&#39; objects. I want to sort the `NSMutableArray` by Person.birthDate which is an `NSDate`.

I think it has something to do with this method:

    NSArray *sortedArray = [drinkDetails sortedArrayUsingSelector:@selector(???)];

In Java I would make my object implement Comparable, or use Collections.sort with an inline custom comparator...how on earth do you do this in Objective-C?


How do I sort an NSMutableArray with custom objects in it?

How do I convert NSMutableArray to NSArray in [tag:Objective-C]?


  [1]: http://en.wikipedia.org/wiki/Objective-C

How do I convert NSMutableArray to NSArray?

The best way to remove duplicate values (`NSString`) from `NSMutableArray` in Objective-C?

Is this the easiest and right way to do it?

    uniquearray = [[NSSet setWithArray:yourarray] allObjects];

The best way to remove duplicate values from NSMutableArray in Objective-C?

I&#39;m looking for a method of turning a NSMutableArray into a string. Is there anything on a par with this Ruby array method?

    &gt;&gt; array1 = [1, 2, 3]
    &gt;&gt; array1.join(&#39;,&#39;)
    =&gt; &quot;1,2,3&quot;

Cheers!

Join an Array in Objective-C

How would I store CGRect objects in a NSMutableArray, and then later retrieve them?

How to store CGRect values in NSMutableArray?

I&#39;m able to put the contents of an `NSSet` into an `NSMutableArray` like this:

    NSMutableArray *array = [set allObjects];

The compiler complains though because [set allObjects] returns an `NSArray` not an `NSMutableArray`. How should this be fixed?

How to return an NSMutableArray from an NSSet

How can an object be added at a specific index of an `NSMutableArray`?

How is an object added to the front of the array?

Adding an object at a specific index of an NSMutableArray

I&#39;ve read all of the related posts regarding this and I am still having an error:

    &#39;Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (5) must be equal to the number of rows contained in that section before the update (5), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).&#39;

Here are the details:

in `.h` I have an `NSMutableArray`:

    @property (strong,nonatomic) NSMutableArray *currentCart;

In `.m` my `numberOfRowsInSection` looks like this:

    - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
    {
        // Return the number of rows in the section.
        
      
        return ([currentCart count]);
       
    }


To enable delete and remove the object from the array:

    // Editing of rows is enabled
    - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
        if (editingStyle == UITableViewCellEditingStyleDelete) {
            
            //when delete is tapped
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            
            [currentCart removeObjectAtIndex:indexPath.row];
    
            
        }
    }

I thought that by having my number of sections relying on the count of the array I&#39;m editing it would ensure the proper number of rows? Can&#39;t this be done without having to reload the table when you delete a row anyway?




&#39;Invalid update: invalid number of rows in section 0

I have tried to initialize my NSMutableArray 100 ways from Sunday, and NOTHING is working for me. I tried setting it equal to a newly allocated and initialized NSMutableArray, just allocating, initializing the variable by itself, every combination I could think of and always the same result.

Here&#39;s the code:

Object.h
    
    NSMutableArray *array;
    
    @property (copy) NSMutableArray *array;

Object.m

    @synthesize array;
    
    if ( self.array ) {
        [self.array addObject:anObject];
    }
    else {
        self.array = [NSMutableArray arrayWithObjects:anObject, nil];
    }

NOTE: In debug &quot;anObject&quot; is NOT nil at time of execution...

I have tested anObject and it isThe initialization works just fine, but I keep getting the error below when I try to addObject: to self.array.

&gt; 2010-07-10 11:52:55.499 MyApp[4347:1807] -[__NSArrayI addObject:]: unrecognized selector sent to instance 0x184480
&gt;
&gt; 2010-07-10 11:52:55.508 MyApp[4347:1807] *** Terminating app due to uncaught exception
&gt; &#39;NSInvalidArgumentException&#39;, reason: &#39;-[__NSArrayI addObject:]: unrecognized selector sent to instance 0x184480&#39;

Does anyone have any idea what&#39;s going wrong?

NSMutableArray addObject: -[__NSArrayI addObject:]: unrecognized selector sent to instance

Is there a way to force NSMutableArray to hold one specific object type only?

I have classes definitions as follow:  

    @interface Wheel:NSObject  
    {    
      int size;  
      float diameter;  
    }  
    @end  
    
      
    @interface Car:NSObject  
    {  
       NSString *model;  
       NSString *make;  
       NSMutableArray *wheels;  
    }  
    @end

How can I force **wheels** array to hold **Wheel** objects only with code? (and absolutely not other objects)

NSMutableArray - force the array to hold specific object type only

So I have a nsmutablearray with a bunch of objects in it.  I want to create a comma separated string of the id value of each object.

Objective-C Simplest way to create comma separated string from an array of objects

What is the difference between `copy` and `mutableCopy` when used on either an `NSArray` or an `NSMutableArray`?


This is my understanding; is it correct?

    // ** NSArray **
    NSArray *myArray_imu = [NSArray  arrayWithObjects:@&quot;abc&quot;, @&quot;def&quot;, nil];
    
    // No copy, increments retain count, result is immutable
    NSArray *myArray_imuCopy = [myArray_imu copy];
    
    // Copys object, result is mutable 
    NSArray *myArray_imuMuta = [myArray_imu mutableCopy];
    
    // Both must be released later
    	
--- 
	
    // ** NSMutableArray **
    NSMutableArray *myArray_mut = [NSMutableArray arrayWithObjects:@&quot;A&quot;, @&quot;B&quot;, nil];
    	
    // Copys object, result is immutable
    NSMutableArray *myArray_mutCopy = [myArray_mut copy];
    
    // Copys object, result is mutable
    NSMutableArray *myArray_mutMuta = [myArray_mut mutableCopy];

    // Both must be released later
    

How do copy and mutableCopy apply to NSArray and NSMutableArray?

I have a UITableView displaying a list of Cities.
I want to separate them by State.  I can&#39;t seem to figure out how to get it to pick the right items out of my Array.
If Section 1 (Arizona) has 2 Cities and Section 2 (California) has 2 Cities, during cellForRowAtIndexPath, Section 2, City 1 has an index of 0, even though it&#39;s the 3rd item in my array.
I thought about just turning my City Array into a State Array, where each item holds an Array of Cities, but I still don&#39;t know what section I&#39;m on and therefore don&#39;t know which City Array under the States Array I would need to access.


UITableView, how do I know what Section during cellForRowAtIndexPath?

I have two `NSMutableArray`&#39;s. They consist of images or text.
The arrays are displayed via a `UITableView`.
When I kill the app the data within the `UITableView` gets lost.
How to save array in `UITableView` by using `NSUserDefault`?



How to save NSMutablearray in NSUserDefaults

What is the difference b/w `NSArray` and `NSMutableArray`?

Difference between NSArray and NSMutableArray

I have declared an `NSMutableArray *categories` in my view controller .h file, and declared a property for it. 

In the `parser:foundCharacters:` method of the `NSXMLParser` delegate in my .m file, I have this code:

    -(void)parser:(NSXMLParser *) parser foundCharacters:(NSString *)string  
    {  
        if (elementFound)  
        {  
            element = string;  
            [self.categories addObject:element];  
        }  
    }

But when I hover over the `[self.categories addObject:element]` line after stepping into it in debug mode, XCode tells me the size is 0x0, 0 objects. There are 3 elements in my XML file so 3 items should be in the array.

I&#39;m missing something really obvious and I can&#39;t figure out what.

NSMutableArray addObject not working

I know I can create an `NSArray` with `@[@&quot;foo&quot;, @&quot;bar&quot;]` or an `NSDictionary` with `@{@0 : @&quot;foo&quot;, @1 : @&quot;bar&quot;}`.

Is there a literal syntax for creating an `NSMutableArray` or an `NSMutableDictionary`?

Is there a literal syntax for mutable collections?

Are there any special methods to make swapping elements in an NSMutableArray easier or more direct?

Swapping elements in an NSMutableArray

    NSArray *array = [[NSArray alloc] initWithObjects:@&quot;ΕΛΤΑ&quot;,
                          @&quot;ΕΛΤΑ COURIER&quot;, @&quot;ACS&quot;, @&quot;ACS ΕΞΩΤΕΡΙΚΟ&quot;, 
                          @&quot;DHL&quot;, @&quot;INTERATTICA&quot;, @&quot;SPEEDEX&quot;, 
                          @&quot;UPS&quot;, @&quot;ΓΕΝΙΚΗ ΤΑΧΥΔΡΟΜΙΚΗ&quot;, @&quot;ΜΕΤΑΦΟΡΙΚΕΣ ΕΞΩΤΕΡΙΚΟΥ&quot;, nil];

This is working because it has nil at the end.

But I add objects like this: `addObject:name` etc...
So at the end I have to add nil I do this addObhect:nil but when I run the app it still crashes at `cellForRowAtIndexPath:`

how can I do this work? 

Ok, I dont have to add nil

What is the reason that my app crashes then?

how to add nil to nsmutablearray?

I have a &lt;code&gt;NSMUtableArray&lt;/code&gt; which has elements, for example:
&lt;pre&gt;
a,b,c,e
&lt;/pre&gt;
And I want to add an object &lt;code&gt;d&lt;/code&gt; to behind &lt;code&gt;c&lt;/code&gt; and before &lt;code&gt;e&lt;/code&gt;.
In other words, I&#39;d like to insert an object to a sorted array.(The object can be a custom object, too)

I&#39;d like to know : besides using &lt;code&gt;for&lt;/code&gt; to find the position, is there any other method to implement it? It is better to use the iOS api.

Thanks.

NSMutableArray add object with order

I&#39;ve been trying to fix this crash for almost a week. The application crashes without any exception or stack-trace. The application does not crash in any way while running through instruments in zombie mode.

I have a method that gets called on a different thread.
The solution that fixed the crash was replacing

    [self.mutableArray removeAllObjects];

with 

    dispatch_async(dispatch_get_main_queue(), ^{
        [self.searchResult removeAllObjects];
    });

I thought it might be a timing issue, so I tried to synchronize it, but it still crashed:

    @synchronized(self)
    {
        [self.searchResult removeAllObjects];
    }

Here is the code

    - (void)populateItems
    {
       // Cancel if already exists	
       [self.searchThread cancel];
    	
       self.searchThread = [[NSThread alloc] initWithTarget:self
                                                   selector:@selector(populateItemsinBackground)
                                                     object:nil];
    	
        [self.searchThread start];
    }
    
    
    - (void)populateItemsinBackground
    {
        @autoreleasepool
        {
            if ([[NSThread currentThread] isCancelled])
    	        [NSThread exit];
    
            [self.mutableArray removeAllObjects];
    
            // Populate data here into mutable array
    
            for (loop here)
            {
                if ([[NSThread currentThread] isCancelled])
    	            [NSThread exit];
    
                // Add items to mutableArray
            }
        }
    }

Is this problem with NSMutableArray not being thread-safe?


Is Objective-C&#39;s NSMutableArray thread-safe?

In a Master-Detail app I&#39;d like to display a TableView with 5 sections titled:

 1. Your Move
 2. Their Move
 3. Won Games
 4. Lost Games
 5. Options

So I create a blank Master-Detail app in Xcode 5.0.2 and then in its MasterViewController.m (which is a UITableViewController) I&#39;m trying to implement the method:

    - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
        return _titles[section];
    }

**My question** is however how to init the NSArray _titles?

I&#39;m trying in the MasterViewController.m:

    #import &quot;MasterViewController.h&quot;
    #import &quot;DetailViewController.h&quot;
    
    static NSArray *_titles_1 = @[
        @&quot;Your Move&quot;,
        @&quot;Their Move&quot;,
        @&quot;Won Games&quot;,
        @&quot;Lost Games&quot;,
        @&quot;Options&quot;
    ];
    
    @interface MasterViewController () {
        NSMutableArray *_games;
        
        NSArray *_titles_2 = @[
                             @&quot;Your Move&quot;,
                             @&quot;Their Move&quot;,
                             @&quot;Won Games&quot;,
                             @&quot;Lost Games&quot;,
                             @&quot;Options&quot;
        ];
    }
    @end
    
    @implementation MasterViewController
    
    - (void)awakeFromNib
    {
        if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPad) {
            self.clearsSelectionOnViewWillAppear = NO;
            self.preferredContentSize = CGSizeMake(320.0, 600.0);
        }
        [super awakeFromNib];
    }
    
    - (void)viewDidLoad
    {
         ....
    }

but both tries above give me syntax errors:

![enter image description here][1]

**UPDATE:**

To my surprise there are many suggestions for this simple question, but as an iOS/Objective-C newbie I&#39;m not sure, which solution is most appropriate.

`dispatch_once` - isn&#39;t it a runtime operation to execute something once in a multi-threaded app? Isn&#39;t it overkill here? I was expecting a compile-time solution for initiating a const array...

`viewDidLoad` - when my app changes between background and foreground, wouldn&#39;t it unnecessary initiate my const array again and again?

Shouldn&#39;t I better set the `NSArray` in `awakeFromNib` (since I use stroyboard scenes for all my ViewControllers)? Or maybe in `initSomething` (is the correct method `initWithStyle`?)

  [1]: http://i.stack.imgur.com/misKY.png

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