Optionals

Declaring
var myString: String?

To check if myString is null

if let myStringValue = myString
{
//will only run if there is a value in myString
}


Note:
- Prevents null references
- Does away with checking for null references
- The question mark indicates that it can contain either nothing or a variable
- When you try to print it, 'nil' will appear
- If it is a null value and you try to append a string to it, you will get an error.
- If there is an error while referencing a null value, swift might add an '!' to the back of the variable, but you should just remove it.


Comments

Post a Comment

Popular posts from this blog

Rotation

Prevent rotation to landscape view: Override the following functions: override var shouldAutorotate: Bool         {         return false     }       override var supportedInterfaceOrientations: UIInterfaceOrientationMask         {         return UIInterfaceOrientationMask.portrait           }
Read more

Things to consider when designing the user interface

Consider the whole user experience. Plan it step by step. Have a prominent search widget and a prominent filter widget. If something is unavailable, rather than taking it away and letting the user guess about whether or not it will be available, list it, indicate it is out of stock and let the user have the option of being alerted once it is in stock. If there is a location feature, allow the user to change location if necessary.  Allow users to clear filter and close panels easily. Give custom suggestions for search and let users view recent search Think of how to make the search experience better.  Ensure that the user has less need to remember things. Think about the questions that your user might need to answer to make a decision and help to provide it. Allow for comparison of products and allow users to bookmark things. Make editing easy. As the user keys in, the screen should scroll down to reveal the next box. Ask for permission only when needed, not at the...
Read more

Swift Basics - Sets

Using the set type: each item must be unique. The items are not ordered. The type stored in the set must be hashable. A basic type (like string, int, double, float) are all hashable. They are able to compute hash values for themselves. To create an initialise a set: var mySet = Set<String>() //initialise values var mySet = Set(["ABC", "DEF", "GHI"]) //instead of var, you can use let Insert items into a set. If we try to insert something that is already there, it will be ignored. mySet.insert("JKL") To check to see if it has been inserted successfully: var results = mySet.insert("JKL") if results.inserted{} Get the number of items in a set: mySet.count Check to see if a set contains an item: var contain = mySet.contains("ABC") //will return true Iterating over each item in a set: for item in mySet { } Removing items in a set: var item = mySet.remove("ABC") mySet.removeAll() Construct sets from 2 sets: var set1 =...
Read more