Yes, that&#39;s possible. The syntax is:

    @interface NSDate (CategoryName) &lt;ProtocolName&gt;
    @end

    @implementation NSDate (CategoryName)
    @end

Here&#39;s [Apple&#39;s documentation][1] on the topic.

It&#39;s also possible to do this using a class extension. I very much like this to privately conform to delegate protocols. Doing so hides the implementation detail of being some delegate of some class from the public interface and removes the dependency from the header.

  [1]: https://developer.apple.com/legacy/library/documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocProtocols.html#//apple_ref/doc/uid/TP30001163-CH15-SW3

I found NPOI is very good to write Excel files with C#.

But I want to open, read and modify Excel files in C#.

How can I do this?

How to read file using NPOI

If I invoke `clone()` method on array of Objects of type A, how will it clone its elements? Will the copy be referencing to the same objects? Or will it call `(element of type A).clone()` for each of them?


Does calling clone() on an array also clone its contents?

I  have a category on NSDate and it would be convenient if it could implement a protocol I previously created. Is this possible? what&#39;s the correct syntax for this?

Can a category implement a protocol in Objective C?

<p>I  have a category on NSDate and it would be convenient if it could implement a protocol I previously created. Is this possible? what's the correct syntax for this?</p>


The question is plain easy and simple, the answer unfortunately not. 

How can you change the font of the text in the `UINavigationBar`?


Change the navigation bar&#39;s font

I want to check if the app is running in the background.

In:

    locationManagerDidUpdateLocation {
        if(app is runing in background){
            do this
        }
    }


Is there any way to check if iOS app is in background?

Struggling with this problem and loath to implement a custom cookie management system.

It appears some hidden level of iOS&#39;s implementation of HTTP fails to manage sessionless cookies properly. Any time an HTTP response sets or deletes a cookie, immediate inspection of NSHTTPCookieStorage cookies will yield the expected results and indicate the correct sessionOnly value.

But if the app quits soon after a response updates cookies, upon relaunch those sessionOnly=FALSE cookies will be reverted to some previous state and the most recent updates lost.

Whether the cookies are set/deleted by a response header or NSHTTPCookieStorage setCookie: makes no difference.

Some caching/syncing voodoo must be going on behind the scenes. The time it takes for the cookie to become persistent can be up to 5 seconds.

ANYONE out there who has or can point to some definitive explanation of this behavior? Is it a bug, plain and simple? Or some undocumented feature whose purpose I can&#39;t comprehend?

Some code you can use to reproduce:

    - (void)applicationDidBecomeActive:(UIApplication *)application
    {
    
        [[NSHTTPCookieStorage sharedHTTPCookieStorage] setCookieAcceptPolicy:NSHTTPCookieAcceptPolicyAlways];
    
        NSHTTPCookie *cookie;
        for (cookie in [NSHTTPCookieStorage sharedHTTPCookieStorage].cookies) {
            NSLog(@&quot;%@=%@&quot;, cookie.name, cookie.value);
        }
    
        NSMutableDictionary *cookieProperties = [NSMutableDictionary dictionary];
        [cookieProperties setObject:@&quot;testCookie&quot; forKey:NSHTTPCookieName];
        [cookieProperties setObject:[NSString stringWithFormat:@&quot;%f&quot;, [[NSDate date] timeIntervalSince1970]] forKey:NSHTTPCookieValue];
        [cookieProperties setObject:@&quot;www.example.com&quot; forKey:NSHTTPCookieDomain];
        [cookieProperties setObject:@&quot;www.example.com&quot; forKey:NSHTTPCookieOriginURL];
        [cookieProperties setObject:@&quot;/&quot; forKey:NSHTTPCookiePath];
        [cookieProperties setObject:@&quot;0&quot; forKey:NSHTTPCookieVersion];
    
        // set expiration to one month from now
        [cookieProperties setObject:[[NSDate date] dateByAddingTimeInterval:2629743] forKey:NSHTTPCookieExpires];
        
        cookie = [NSHTTPCookie cookieWithProperties:cookieProperties];
        [[NSHTTPCookieStorage sharedHTTPCookieStorage] setCookie:cookie];
    
    }

This code should output a new value on every launch. Instead you will see that if you quit the app quickly the value is unchanged.

Some possibly related stack overflow questions:

[https://stackoverflow.com/questions/4623811/iphone-nshttpcookiestorage-avaible-on-app-reopen][1]


[https://stackoverflow.com/questions/2662530/iphone-nshttpcookie-is-not-saved-across-app-restarts][2]


[https://stackoverflow.com/questions/5747012/nshttpcookies-refuse-to-be-deleted][3]


[https://stackoverflow.com/questions/5070446/deleted-nshttpcookie-returns-if-app-is-terminated][4]


  [1]: https://stackoverflow.com/questions/4623811/iphone-nshttpcookiestorage-avaible-on-app-reopen
  [2]: https://stackoverflow.com/questions/2662530/iphone-nshttpcookie-is-not-saved-across-app-restarts
  [3]: https://stackoverflow.com/questions/5747012/nshttpcookies-refuse-to-be-deleted
  [4]: https://stackoverflow.com/questions/5070446/deleted-nshttpcookie-returns-if-app-is-terminated

NSHTTPCookieStorage state not saved on app exit. Any definitive knowledge/documentation out there?

I am having a tableview and I want to know that how can I change the selected row&#39;s text color, say to Red ? I tried by this code : 

    - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
    {
    	static NSString *CellIdentifier = @&quot;Cell&quot;;
    
        UITableViewCell *cell= [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:nil] autorelease];
    	
    	cell.text = [localArray objectAtIndex:indexPath.row];
    	
    	return cell;
    }
    
    - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
    {
    	cityName = [localArray objectAtIndex:indexPath.row];
    	
    	UITableViewCell* theCell = [tableView cellForRowAtIndexPath:indexPath];
    	theCell.textColor = [UIColor redColor];
    	//theCell.textLabel.textColor = [UIColor redColor];
    
    	[tableView deselectRowAtIndexPath:indexPath animated:NO];
    }

(1) When I select any row then text color changed to the red but when I select another then previously selected row&#39;s text remains red. how can I solve this ? 

(2) When I scroll the table text color change to the black color how to solve this ?

Thanks..

UITableViewCell selected row&#39;s text color change

I know how to add an IBAction to a button by dragging from the interface builder, but I want to add the action programmatically to save time and to avoid switching back and forth constantly. The solution is probably really simple, but I just can&#39;t seem to find any answers when I search it. Thank you!

How do you add an action to a button programmatically in xcode

Given an `NSArray` of `NSDictionary` objects (containing similar objects and keys) is it possible to write perform a map to an array of specified key? For example, in Ruby it can be done with:

    array.map(&amp;:name)

NSArray Equivalent of Map

When compiling this code, I get the error &quot;initializer element is not a compile-time constant&quot;. Can anyone explain why?

    #import &quot;PreferencesController.h&quot;
    
    @implementation PreferencesController
    
    - (id)init
    {
        self = [super init];
        if (self) {
            // Initialization code here.
        }
        
        return self;
    }
    
    
    NSImage* imageSegment = [[NSImage alloc] initWithContentsOfFile:@&quot;/User/asd.jpg&quot;];//error here



Compiler error: &quot;initializer element is not a compile-time constant&quot;

Recently I started Unit testing my application. This project (in Xcode4) was created without a unit test bundle so I had to set it up.
I have followed the steps from here: http://cocoawithlove.com/2009/12/sample-mac-application-with-complete.html
And It was working well for simple classes but now I am trying to test a class that depends on another and that on another, etc.

First I got a linker error so I added `*.m` files to the test case target but now I get a warning for every class I am trying to test: 

&gt; Class Foo is implemented in both MyApp
&gt; and MyAppTestCase. One of the two will
&gt; be used. Which one is undefined.

I wonder why is that? How can I solve this? Maybe I missed something when setting the unit test target?


### Edit - The Solution

* Set &quot;Bundle Loader&quot; correctly to `$(BUILT_PRODUCTS_DIR)/AppName.app/AppName`


* Set &quot;Symbols Hidden by Default&quot; to **NO** (in Build Settings of the target application). This is where the linker errors come from because it is YES by default!. I&#39;ve been struggling with this for so long!.

Source: https://stackoverflow.com/questions/6461074/linking-error-for-unit-testing-with-xcode-4


Class Foo is implemented in both MyApp and MyAppTestCase. One of the two will be used. Which one is undefined

How can I have a two-digit integer in a a string, even if the integer is less than 10?

    [NSString stringWithFormat:@&quot;%d&quot;, 1] //should be @&quot;01&quot;


Make a two-digit string from a single-digit integer

I am currently receiving a string like this:

    @&quot;Sam|26,Hannah|22,Adam|30,Carlie|32,Jan|54&quot;

And I am splitting it like this:

    testArray = [[NSArray alloc] init];
    NSString *testString = [[NSString alloc] initWithFormat:@&quot;Sam|26,Hannah|22,Adam|30,Carlie|32,Jan|54,Steve|56,Matty|24,Bill|30,Rob|30,Jason|33,Mark|22,Stuart|54,Kevin|30&quot;];
    testArray = [testString componentsSeparatedByString:@&quot;,&quot;];
    	
    dict = [NSMutableDictionary dictionary];
    for (NSString *s in testArray) {
    		
        testArray2 = [s componentsSeparatedByString:@&quot;|&quot;];
        [dict setObject:[testArray2 objectAtIndex:1] forKey:[testArray2 objectAtIndex:0]];
    }

I will now be receiving a string like this:

    @&quot;Sam|26|Developer,Hannah|22|Team Leader,Adam|30|Director,Carlie|32|PA,Jan|54|Cleaner&quot;

Can I (and how) use the same method as above to separate the string more than once using the &quot;|&quot; separator?

Split NSString multiple times on the same separator

What is the difference between TCP and UDP? 

I know that TCP is used in the case of non-time critical applications, and UDP is used for games or applications that require fast transmission of data. I know that TCP is used for HTTP, HTTPs, FTP, SMTP, and Telnet. I know that UDP is used for DNS and DHCP.

But why? What characteristics of TCP and UDP make it useful for their respective use cases? 

Difference between TCP and UDP?

I have two `view controllers A` and `B`, and they both have each other as their delegates.

When I did nothing except define the protocols at the beginning of the header files and `#import` the other&#39;s header file, I got two errors along the lines of -

&gt; cannot find protocol declaration for &quot;BDelegate&quot;, which was showing in
&gt; A.h (where I wrote &lt;BDelegate&gt;) cannot find protocol declaration for
&gt; &quot;ADelegate&quot;, which was showing in B.h (where I wrote  &lt;ADelegate&gt;)


Looking online, people had written earlier that the circular inclusion of header files could be leading to the problems. They recommended either using `#include` instead, or `@class` declaration like -

    @class A

instead of

    #import A.h

inside `#import B.h`

I have tried almost every combination of these imports, and `@classes`, and `#include` but still can&#39;t get rid of the warnings. Also, solutions online recommended moving the `#import` to the `.m` files but that didn&#39;t help either. Part of the reason is that the solutions online are kinda fuzzy - if you could break it down that would be great.

Any suggestions about what can be done to fix this?


--------------------------------------------------
**-- BigViewController.h --**

    
    #import &quot;BaseViewController.h&quot;
    #include &quot;BaseViewController.h&quot;
    
    @class BigViewController;
    
    @protocol BigViewControllerDelegate
    -(void) BigViewController:(BigViewController *) bigView;
    @end
    
    @interface BigViewController : UIViewController &lt;BaseViewControllerDelegate&gt;
    {    
         //delegate
         id &lt;BigViewControllerDelegate&gt; delegate;
    
    ivars...	
    }
    
    @properties...
    @end
    
    --------------------------------------------------
    
**-- BaseViewController.h --**

    #&lt;UIKit/UIKit.h&gt;
    
    #import &quot;BigViewController.h&quot;
    #include &quot;BigViewController.h&quot;
    
    @class BigViewController;
    
    @protocol BaseViewControllerDelegate
    - (void) setParametersWithItemChosen:(Item *) item;
    @end
    
    @interface BaseViewController : UIViewController &lt;...BigViewControllerDelegate...&gt;
    {
    
       ivars...
    
       //delegate
        id &lt;BaseViewControllerDelegate&gt; delegate;
    }
    
    @properties...
    @end
    




Cannot find protocol declaration

I need to extract the full protocol, domain, and port from a given URL. For example:

    https://localhost:8181/ContactUs-1.0/contact?lang=it&amp;report_type=consumer
    &gt;&gt;&gt;
    https://localhost:8181

Get protocol, domain, and port from URL

 - How can I send and receive messages on the server side using WebSocket, as per the protocol?

 - Why do I get seemingly random bytes at the server when I send data from the browser to the server? It the data encoded somehow?

 - How does the framing work in both the server &amp;rarr; client and client &amp;rarr; server directions?


How can I send and receive WebSocket messages on the server side?

Is there a reason we include the `http` / `https` protocol on the `href` attribute of links?

Would it be fine to just leave it off:

    &lt;a href=&quot;example.com&quot;&gt;my site&lt;/a&gt;

html - links without http protocol

I want to use a selector on an NSObject instance *without* the need for an implemented protocol. For example, there&#39;s a category method that should set an error property if the NSObject instance it&#39;s called on supports it. This is the code, and the code works as intended:

    if ([self respondsToSelector:@selector(setError:)])
    {
        [self performSelector:@selector(setError:) withObject:[NSError errorWithDomain:@&quot;SomeDomain&quot; code:1 userInfo:nil]];
    }

However, the compiler doesn&#39;t see any method around with the setError: signature, so it gives me a warning, for each line that contains the `@selector(setError:)` snippet:

    Undeclared selector &#39;setError:&#39;

I don&#39;t want to have to declare a protocol to get rid of this warning, because I don&#39;t want all classes that may use this to implement anything special. Just by convention I want them to have a `setError:` method or property.

Is this doable? How?

Cheers,  
EP

How to get rid of the &#39;undeclared selector&#39; warning

As I cannot create a synthesized property in a Category in Objective-C, I do not know how to optimize the following code:

    @interface MyClass (Variant)
    @property (nonatomic, strong) NSString *test;
    @end

    @implementation MyClass (Variant)

    @dynamic test;

    - (NSString *)test {
        NSString *res;
        //do a lot of stuff
        return res;
    }

    @end

The *test-method* is called multiple times on runtime and I&#39;m doing a lot of stuff to calculate the result. Normally using a synthesized property I store the value in a IVar _test the first time the method is called, and just returning this IVar next time. How can I optimized the above code?

Objective-C: Property / instance variable in category

Looking to pull the category ID of a specific page in WordPress that is listing all posts using that specific category.  Tried the below but not working.  I am able to get the category name using `single_term_title`.

    $category = single_term_title(&quot;&quot;, false);
    $catid = get_cat_ID( $category );

`$category` is displaying &quot;Entertainment&quot; for example. But I also need the ID of &quot;Entertainment&quot;.  How would I go about this?

Get current category ID of the active page

I would like to remove the category &amp; tag base from WordPress URL. I have come across other posts and solutions which used plugins. I would like to stay away from plugins and have a solution from within functions.php. This would prevent any future plugin updates or WordPress default files from being changed. 

Any help would be appreciated. Thanks!

I have tried these solutions so far:

- This htaccess solution did not work: http://mikepayne.co/2011/remove-category-base-from-url/
- These methods also failed: http://www.askapache.com/wordpress/remove-category-wordpress-urls.html

Remove category &amp; tag base from WordPress url - without a plugin

I want to create a category on `UIColor` in my app using Xcode 6. But the thing is that in Xcode 6 there is no Objective-C category file template. 

Is there any option to create a category in Xcode 6?



Content Type	Original Author	Original Content on Stackoverflow
Question	cfischer	View Question on Stackoverflow
Solution 1 - Objective C	Nikolai Ruhe	View Answer on Stackoverflow

Can a category implement a protocol in Objective C?

Objective C Problem Overview

Objective C Solutions

Solution 1 - Objective C

Does calling clone() on an array also clone its contents?

How to read file using NPOI

Attributions