UITableViewCell's contentView gets unwanted "height=44" constraint. Crashlytics: iOS 9 workaround for binary image loading issue in place. iTunes Connect - Get active user installs by app version. How can I use an existing private key to a new iOS development certificate?. Never use as! for down casting, even if you are pretty sure. For down casting the very first and last choice should be to use as?, as it will give us the chance to verify at-lest the return instance is nil or not. It is almost ok to use as when it comes to upcasting. The very first practice is to avoid type cast. But I can confirm life will be much more easier if you start to follow the practice for type casting. This is a heavily opinion based practice, you are always welcome to discard or embrace the following practice. On the above example we are just checking if the label is a UIView or not. : Playground - noun: a place where people can play And finally accessing the property of a nil instance causing the crash.īy the way we have already a blog post on optional, force unwrapping and etc. Force down casting the labelView to UIButton causes a nil instance. On the above example when we are force down casting the labelView to UILabel then it seems very ok, but things will get messy when we try to convert the wrong type cast. The most dangerous type casting operator. : Playground - noun: a place where people can playĬhildButton.tintColor //error: Execution was interrupted, reason: signal SIGABRT. Will potentially crash the app when force downcast will return nil. Force downcast through as!Īs! is used for forced downcast. But when we try to convert the labelView to UIButton, which is also a subclass of UIView, through as? we are getting a nil. Then we start to convert the labelView again to UILabel through as? which successes and we can print the text property of UILabel. Let childButton = labelView as? UIButton // failsĪs we can see on the above example, label is type casted to UIView. Let childLabel = labelView as? UILabel // success On successful conversion it will return the child object on failure case will return nil. DownCast through as?Īs? is used on DownCast by an implicit way or a safe way. As we know UILabel is inherited from UIView on UIKit framework. On the above example we are upcasting the label, which itself is a UILabel, to its parent class UIView. Let label = UILabel(frame: CGRect(x: 0, y: 0, width: 100, height: 100)) as has three different variance based on operation they perform.Īs is the Upcast operator on Swift. On swift we use as as the type cast operator. #Downcast only unwraps optionals how to
At the end we will have a small talk on how to avoid type cast.
the basic of how type cast works on Swift.Once you start to make a habit of crossing that road times to times, you will find yourself on deep pitfall very soon.īut anyway here we are on that difficult road, to understand: Today we gonna talk about type casting, one little road I will never want to cross. In the simplest term, type casting is to convert one type of instance to another. So let us not delay on type casting deep dive. Some five minutes reading can save some long anxious hours. Swift also provides us three as variance for type Casting. One of them is is which is the type checker. Swift has some very cool techniques for handling type casting, on its arsenal. Lack of knowledge on type casting can drive us to some serious bugs those are nightmare for any developer, senior or junior. On the initial stage type casting seems very ok, but on the long run it always bites us back.
0 kommentar(er)
