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ios interview questions

Top ios frequently asked interview questions

Codesign error: Provisioning profile cannot be found after deleting expired profile

Tried to rebuild an app that was just working yesterday. Got a message that a profile had expired, so I removed it from the iPod and from iTunes. When I chose a new profile (one with an * in the identifier), I now get an error:

Code Sign Error: Provisioning Profile (long string) can't be found.

What am I missing? I looked through related questions and didn't see this scenario already. Thanks


Source: (StackOverflow)

How to develop or migrate apps for iPhone 5 screen resolution?

The new iPhone 5 display has a new aspect ratio and a new resolution (640 x 1136 pixels).

What is required to develop new or transition already existing applications to the new screen size?

What should we keep in mind to make applications "universal" for both the older displays and the new widescreen aspect ratio?


Source: (StackOverflow)

How to check for an active Internet connection on iPhone SDK?

I would like to check to see if I have an Internet connection on the iPhone using the Cocoa Touch libraries.

I came up with a way to do this using an NSURL. The way I did it seems a bit unreliable (because even Google could one day be down and relying on a third party seems bad), and while I could check to see for a response from some other websites if Google didn't respond, it does seem wasteful and an unnecessary overhead on my application.

- (BOOL) connectedToInternet
{
    NSString *URLString = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com"]];
    return ( URLString != NULL ) ? YES : NO;
}

Is what I have done bad? (Not to mention stringWithContentsOfURL is deprecated in 3.0) And if so, what is a better way to accomplish this?


Source: (StackOverflow)

What's the difference between the atomic and nonatomic attributes?

What do atomic and nonatomic mean in property declarations?

@property(nonatomic, retain) UITextField *userName;
@property(atomic, retain) UITextField *userName;
@property(retain) UITextField *userName;

What is the operational difference between these three?


Source: (StackOverflow)

Vertically align text to top within a UILabel

I have a UILabel with space for two lines of text. Sometimes, when the text is too short, this text is displayed in the vertical center of the label.

How do I vertically align the text to always be at the top of the UILabel?

image representing a UILabel with vertically-centered text


Source: (StackOverflow)

Placeholder in UITextView

I'm making an application which uses an UITextView. Now I want the UITextView to have a placeholder similar to the one you can set for an UITextField.

Does anyone know how to do this?


Source: (StackOverflow)

How to change the name of an iOS app?

I began an iPhone project the other day with a silly development code name, and now I want to change the name of the project since its nearly finished.

But I'm not sure how to do this with Xcode, trying the obvious of changing the application's name in the pinfo, causes the signing process to go wrong (I think...) and my app won't launch giving me a Launcher error.

I guess I could make a new project and copy paste everything over, but it seems so primitive, that I'm hoping for a more civilized solution.


Source: (StackOverflow)

How to sort an NSMutableArray with custom objects in it?

What I want to do seems pretty simple, but I can't find any answers on the web. I have an NSMutableArray of objects, let's say they are 'Person' 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?


Source: (StackOverflow)

How can I develop for iPhone using a Windows development machine?

Is there any way to tinker with the iPhone SDK on a Windows machine? Are there plans for an iPhone SDK version for Windows?

The only other way I can think of doing this is to run a Mac VM image on a VMWare server running on Windows, although I'm not too sure how legal this is.


Source: (StackOverflow)

Loaded nib but the view outlet was not set - new to InterfaceBuilder

I added a new nib file to my project, and all I want to do is have it display on the screen for now.

However, when I click on the toolbar icon that is supposed to take me to the view that I created, I get an NSInternalInconsistencyException with the message:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "..." nib but the view outlet was not set.'

So I opened up my nib file, and I see for the view that there are no referencing outlets set. However, I try to click and drag the circle for "new referencing outlet" to File Owner, but it won't let me...what do I need to do to get my view to display?

Thanks.


Source: (StackOverflow)

Convert UTF-8 encoded NSData to NSString

I have UTF-8 encoded NSData from windows server and I want to convert it to NSString for iPhone. Since data contains characters (like a degree symbol) which have different values on both platforms, how do I convert data to string?


Source: (StackOverflow)

How do I animate constraint changes?

I'm updating an old app with an AdBannerView and when there is no ad, it slides off screen. When there is an ad it slides on screen. Basic stuff.

Old style, I set the frame in an animation block. New style, I have a IBOutlet to the constraint which determines the Y position, in this case it's distance from the bottom of the superview, and modify the constant.

- (void)moveBannerOffScreen {
    [UIView animateWithDuration:5
             animations:^{
                          _addBannerDistanceFromBottomConstraint.constant = -32;
                     }];
    bannerIsVisible = FALSE;
}

- (void)moveBannerOnScreen {
    [UIView animateWithDuration:5
             animations:^{
                         _addBannerDistanceFromBottomConstraint.constant = 0;
             }];
    bannerIsVisible = TRUE;
}

And the banner moves, exactly as expected, but no animation.

UPDATE: I re-watched WWDC12 video "Best Practices for Mastering Auto Layout" which covers animation. It discusses how to update constraints using CoreAnimation.

enter image description here enter image description here

I've tried with the following code, but get the exact same results.

- (void)moveBannerOffScreen {
    _addBannerDistanceFromBottomConstraint.constant = -32;
    [UIView animateWithDuration:2
                     animations:^{
                         [self.view setNeedsLayout];
                     }];
    bannerIsVisible = FALSE;
}

- (void)moveBannerOnScreen {
    _addBannerDistanceFromBottomConstraint.constant = 0;
    [UIView animateWithDuration:2
                     animations:^{
                         [self.view setNeedsLayout];
                     }];
    bannerIsVisible = TRUE;
}

On a side note, I have checked numerous times and this is being executed on the main thread.


Source: (StackOverflow)

Can I embed a custom font in an iPhone application?

This question relates to iOS pre-3.2. As of 3.2 this functionality is easily achievable using samvermette's answer below, and I have changed the Accepted Answer (from commanda to samvermette) to reflect this. I can't give credit to both answers (besides uproots) but they are both good.

I would like to have an app include a custom font for rendering text, load it, and then use it with standard UIKit elements like UILabel. Is this possible?

I found these links:

but these would require me to render each glyph myself, which is a bit too much like hard work, especially for multi-line text.

I've also found posts that say straight out that it's not possible, but without justification, so I'm looking for a definitive answer.


EDIT - failed -[UIFont fontWithName:size:] experiment

I downloaded Harrowprint.tff (downloaded from here) and added it to my Resources directory and to the project. I then tried this code:

UIFont* font = [UIFont fontWithName:@"Harrowprint" size:20];

which resulted in an exception being thrown. Looking at the TTF file in Finder confirmed that the font name was Harrowprint.


EDIT - there have been a number of replies so far which tell me to read the documentation on X or Y. I've experimented extensively with all of these, and got nowhere. In one case, X turned out to be relevant only on OS X, not on iPhone. Consequently I am setting a bounty for this question, and I will award the bounty to the first person who provides an answer (using only documented APIs) who responds with sufficient information to get this working on the device. Working on the simulator too would be a bonus.


EDIT - It appears that the bounty auto-awards to the answer with the highest number of votes. Interesting. No one actually provided an answer that solved the question as asked - the solution that involves coding your own UILabel subclass doesn't support word-wrap, which is an essential feature for me - though I guess I could extend it to do so.


Source: (StackOverflow)

How to change Status Bar text color in iOS 7

My application has a dark background, but in iOS 7 the status bar became transparent. So I can't see anything there, only the green battery indicator in the corner. How can I change the status bar text color to white like it is on the home screen?


Source: (StackOverflow)