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📲 The curated list of iOS Developer interview questions and answers, Swift & Objective-C
With @IBInspectable and @IBDesignable, its possible to build a custom interface for confugring your custom controls and have them rendered in real-time while designing your project.
@IBInspectible properties provide new access to an old feature:
user-defined runtime attributes. Currently accessible from the identity inspector, these attributes have been available since before Interface Builder was integrated into Xcode. They provide a powerful mechanism for configuring any key-value coded property of an instance in a NIB, XIB, or storyboard.
Built-in Cocoa types can also be extended to have inspectable properties beyond the ones already in Interface Builder's attribute inspector. If you like rounded corners, you'll love this UIView extension:
extension UIView {
@IBInspectable var cornerRadius: CGFloat {
get {
return layer.cornerRadius
}
set {
layer.cornerRadius = newValue
layer.masksToBounds = newValue > 0
}
}
}
The attribute @IBDesignable lets Interface Builder perform live updates on a particular view.
This allows seeing how your custom views will appear without building and running your app after each change.
To mark a custom view as IBDesignable, prefix the class name with @IBDesignable (or the IB_DESIGNABLE macro in Objective-C). Your initializers, layout, and drawing methods will be used to render your custom view right on the canvas:
@IBDesignable
class MyCustomView: UIView {
...
}
Here are a few common ways to specify the layout elements in a UIView:
Using Interface Builder, you can add a XIB file to your project, layout elements within it, and then load the XIB in your application code (either automatically, based on naming conventions, or manually).
Also, using InterfaceBuilder you can create a storyboard for your application.
You can write your own code to use NSLayoutConstraints to have elements in a view arranged by Auto Layout.
You can create CGRects describing the exact coordinates for each element and pass them to UIView's
-(id)initWithFrame:(CGRect)frame method.
A size class is a new technology used by iOS to allow you to custom your app for a given device class, based on its orientation and screen size.
There are presently four classes:
The Intrinsic Content Size is one of the most powerful features you gain when you opt-in to using Auto Layout to describe your interfaces. When a view has an intrinsic content size, it is promising Auto Layout that it will have a predefined size that the engine can use to calculate and lay out its views.
The bounds of an UIView is the rectangle, expressed as a location(x, y) and size (width, height) relative to its own coordinate system (0,0) The frame of an UIView is the rectangle, expressed as a location(x, y) and size(width, height) relative to the superview it is contained within.
Let's take an example of UIScrollView:
UIScrollView's bounds.origin will not be (0, 0) when its contentOffset is not (0, 0).
Layer objects are data objects when represents visual content. Layer objects are used by views to render their content. Custom layer objects can also be added to the interface to implement complex animations and other types of sophisticated visual effects.
Two points to be remembered:
loadNibNamed: or initWIthNibName:.So you created a fancy view with lots of button, subviews etc. If you want to modify any of these views / objects any time after loading the nib FROM the loading objects (usually a view or window controller) you set outlets for these objects to the file owner. It's that simple.
This is the reason why by default all View Controller of Window Controllers act as file owners, and also have an outlet to the main window or view object in the nib file: because duh, if you're controlling something you'll definitely need to have an outlet to it so that you can send messages to it.
The reason it's called file owner and given a special place, is because unlike the other objects in the nib, the file owner is external to the nib and is not part of it. In fact, it only becomes available when the nib is loaded. So the file owner is a stand-in or proxy for the actual object which will later load the nib.
application:willFinishLaunchWithOptions:- This method is your app's first chance to excute code at launch time.
application:didFinishLaunchingWithOptions:- This method allows you to perform any final initialization before your app is displayed to the user.
applicationDidBecomeActive:-Lets your app know that it is about to become the foreground app. Use this method for any last minute perpration.
applicationWillResignActive:- Lets you know that your app is transitioning away from being the foreground app. Use this method to put your app into a quiescent state.
applicationDidEnterBacground:- Lets you know that your app is now running in the background and may be suspended at any time.
applicationWillEnterForeground:- Lets you know that your app is moving out of the background and back into foreground, but that it is not yet active.
applicationWillTerminate:- Lets you know that your app is being terminated. This method is not called if your app is suspended.
Tests the smallest unit of functionality, typically a method/function (e.g. given a class with a particular state, calling x method on the class should cause y to happen). Unit tests should be focussed on one particular feature (e.g., calling the pop method when the stack is empty should throw an InvalidOperationException). Everything it touches should be done in memory; this means that the test code and the code under test shouldn't:
Any kind of dependency that is slow/hard to understand / initialize / manipulate should be stubbed / mocked / whatevered using the appropriate techniques so you can focus on what the unit of code is doing, not what its dependencies do. In short, unit tests are as simple as possible, easy to debug, reliable(due to reduced external factors), fast to execute and help to prove that the smallest building blocks of your program function as intended before they're put together. The caveat is that, although you can prove they work perfectly in isolation, the units of code may blow up when combined which brings us to ...
Integration tests build on unit tests by combining the units of code and testing that the resulting combination functions correctly. This can be either the innards of one system,mor combining multiple systems together to do something useful. Also, another thing that defferentiates integration tests from unit tests is the environment, Integration tests can and will use threads, access the database or do whatever is required to ensure that all of the code and the different environment changes will work correctly.
If you've built some serialization code and unit tested its innards without touching the disk, how do you know that it'll work when you are loading and saving the disk? Maybe you forgot to flush and dispose filestreams. Maybe your file permissions are incorrect and you've tested the innards using in memory streams. The only way to find out for sure is to test it 'for real' using an environment that is closest to production.
The main advantage is that they will find bugs that unit tests can't such as wiring bugs (e.g. an instance of class A unexpectedly receives a null instance of B) and environment bugs (it runs fine on my single-CPU machine, but my colleague's 4 core machine can't pass the tests). The main disadvantage is that integration tests touch more code, are less reliable, failures are harder to diagnose and the tests are harder to maintain.
Also, integration tests don't necessarily prove that a complete feature works. The user may not care about the internal details of my programs, but I do!
Functional tests check a particular feature for correctness by comparing the results for a given input against the specification. Functional tests don't concern themselves with intermediate results or side-effects, just the result (they don't care that after doing x, object y has state z). They are written to test part of the specification such as, "calling function Square(x) with the argument of 2 returns 4".
Acceptance testing seems to be split into two types: Standard acceptance testing involves performing tests on the full system (e.g. using your web page via web browser) to see whether the application's functionaluty satisfies the specification. E.g. "clicking a zoom icon should enlarge the document view by 25%" There is no real continuum of results, just a pass or fail outcome.
The advantage is that the tests are described in plain english and ensures the software, as a whole, is feature complete. The disadvantage is that you've moved another level up the testing pyramid. Acceptance tests touch mountains of code, so tracking down a failure can be tricky.
Also, in agile software development, user acceptance testing involves creating tests to mirror the user stories created by/for the software's customer during development. If the tests pass, it means the software should meet the customer's requirements and the stories can be considered complete. An acceptance test suite is basically an executable specification written in a domain specific language that describes the tests in the language used by the users of the system.
Tests gives us a clear perspective on the API design, by getting into the mindset of being a client of the API before it exists. Good tests serve as great documentation of expected behavio