Our DNA is written in Objective-C

Category Archive for ‘Q&A’ rss

TopLayoutGuide 97 Pixels?!

When implementing iOS 7 support for a client’s app I got a result that might stump even seasoned Cocoa programmers.

On iOS 7 views generally go behind translucent bars. To still get your views aligned correctly – when creating them in code – you have to get the responsible view controller’s top and bottom layout guides.

Those get set sometime before viewWillLayoutSubviews and I found it useful to add a viewInset property to the view controller’s base view. Setting this would setNeedsLayout and then you can rearrange the subviews according to the new insets in layoutSubviews.

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Implicit IVAR Synthesis

Apple recently added the ability for Xcode to automatically create instance variables for you. This means you no longer need to add an @synthesize for each property you create.

But does it really do that always, or are there scenarios where no _ivar is needed? Are there situations wehre you do need an explicit synthesis? For example what about properties which are just passing through values to a sub-object?

I wanted to know, so I experimented a bit. I even filed a Radar with Apple for clarification which came back with a good explanation.

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Undefined Symbols

OC asks:

“I’m doing some Objective-C exercises from a Big Nerd Ranch book, and I’m getting these errors. I’m still pretty lost in terms of how to handle unexpected errors and stuff, so I would appreciate the help.”

I’m going into go into much greater depth here answering this question, because of “teaching a man to fish”, ya’know.

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DTCoreText: Centering an Image

Amy Worall asks:

How do I centre an image in DTCoreText? I’m working with attributed strings not HTML. Any sample code?

In this blog post will answer this.

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Using Custom Fonts with DTCoreText

Friend of DTCoreText Holger was having problems getting DTCoreText to use the bold font face of his custom font.

I want to take this opportunity to explain what the root cause for Holger’s problem was and what you need to know if you’re using custom fonts with DTCoreText.

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Today’s Hero: CHEN Xian’an

I was having a problem in DTCoreText where the multi-byte sequence making up an Emoji would not get properly encoded by DTHTMLWriter. A quick peeking into NSHTMLWriter didn’t bring relief either, Apple is not encoding these characters, but leaves them unencoded.

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Zarra on Locking

In my previous article dealing with Multi-Context Core Data I introduced a 3-context scheme that Marcus Zarra hat shown us in a back room at the 2012 NSConference.

Several people inquired about Locking, take for example Wim Fikkert:

Thanks for the great article. However, like Tom, I was wondering if the main context will not be blocked whenever you perform a save to disk with the persistent store. I am using the last design pattern, and I keep running into my app locking up. I have done some more searching and came across this article. Perhaps you can comment?

I don’t pretend to come anywhere close to being the Core Data expert that Zarra is, so I went straight to the horses mouth and asked him.

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How to send image to remote server

Somebody asked on StackOverflow:

how to send image to Remote server from the below code last string is placed with image

NSString *reqString=[NSString stringWithFormat:@”http://projeceads.info/spir/productinfo/productadd/%@/%@/%@/%@/%@/%@/%@/%@”,ownerId,productNameTxt.text,QuantityTxt.text,sizeTxt.text,ageTxt.text,priceTxt.text,descriptionView.text,imgstr]; NSURL *reqUrl=[NSURL URLWithString:reqString]; NSURLConnection *connection=[[NSURLConnection alloc]initWithRequest:[NSURLRequest requestWithURL:reqUrl] delegate:self];
[connection start]; }

Now there are several things wrong with this question. This is the very first question this person asked on StackOverflow and he didn’t even set a proper user name yet. The code is not formatted as such, the English is bad and to most casual onlookers it is unclear what this question is about.

Still I felt an urge to give a good answer because often it is non-sensical questions like this that challenge our ability to parse the intent of the asking person and our knowledge of the subject matter. It is also such a situation where you can give an answer that exactly matches the question as well as a second answer that is a better way of achieving the intent.

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Assorted Observations

While I am developing my first own Mac app I’ve been adding to this blog post whenever something was weird to me. Or simply different.

You can definitely see in many instances how some modus operandi on iOS has its roots on Mac, but Apple had to change things a bit around to accomodate the different UI paradigms on the mobile platform.

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CoreLocation Background Update Messaging

Two years ago I put together revolutionary chart that detailed the flow of delegate messages when sending an app into background. This was even featured by Erica Sadun of TUAW because it for the first time visualized the whole process in a easy to understand way.

Based on this chart Carl Brown from PDAgent made an addendum to deal with the special case of background region updates and sent it to me. To my shame I have to admit that it was sitting at the bottom of my inbox for 4 months now and it is only now that in my effort to reach Inbox Zero I am dealing with this and putting it up here for your viewing pleasure.

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