![]() If you use as! and object(forKey:) returned nil, you'll get a crash, so I really don't recommend it unless you're absolutely sure. Use as? to optionally typecast your object to the type it should be.Use as! to force typecast your object to the data type it should be.You're faced with two options, one of which isn't smart so you realistically have only one option! It's object(forKey:) that will cause you the most bother, because you get an optional object back. Knowing the return values are important, because if you use bool(forKey:) and get back "false", does that mean the key didn't exist, or did it perhaps exist and you just set it to be false? ![]() object(forKey:) returns Any? so you need to conditionally typecast it to your data type.double(forKey:) returns a double if the key existed, or 0.0 if not.float(forKey:) returns a float if the key existed, or 0.0 if not.bool(forKey:) returns a boolean if the key existed, or false if not.integer(forKey:) returns an integer if the key existed, or 0 if not. ![]() When you're reading values from UserDefaults you need to check the return type carefully to ensure you know what you're getting. That's enough about writing for now let's take a look at reading. Using set() for these advanced types is just the same as using the other data types: t("Paul Hudson", forKey: "Name")Įven if you're trying to save complex types such as arrays and dictionaries, UserDefaults laps it up: let array = ĭt(array, forKey: "SavedArray") ![]() But UserDefaults was written for NSString and friends – all of which are 100% interchangeable with Swift their equivalents – which is why this code works. Now, here's a curiosity that's worth explaining briefly: in Swift, strings, arrays and dictionaries are all structs, not objects. You can also use the set() to store strings, arrays, dictionaries and dates. Here are some examples: let defaults = UserDefaults.standard These values nearly always have no meaning outside of what you use them for, so just make sure the key names are memorable. Once that's done, it's easy to set a variety of values – you just need to give each one a unique key so you can reference it later. To get started with UserDefaults, you create a new instance of the class like this: let defaults = UserDefaults.standard You might find it useful to create a fresh Single View App project just so you can test out the code. If you think your saved data would take up more than say 100KB, UserDefaults is almost certainly the wrong choice.īefore we get into modifying project 10, we're going to do a little bit of test coding first to try out what UserDefaults lets us do. This makes using it really easy, but you need to know that it's a bad idea to store lots of data in there because it will slow loading of your app. When you write data to UserDefaults, it automatically gets loaded when your app runs so that you can read it back again. You can write basic types such as Bool, Float, Double, Int, String, or URL, but you can also write more complex types such as arrays, dictionaries and Date – and even Data values. standard.You can use UserDefaults to store any basic data type for as long as the app is installed. into our program as "-path": guard let path = UserDefaults. Just like when performing network calls, URLs are used to point to various locations on disk, which we can then either read binary data from, or write new data into.įor example, here we’re retrieving a file path passed as an argument to a Swift command line tool, which we then turn into a file system URL in order to load that file’s data: // This lets us easily access any command line argument passed URLs, locations, and dataįundamentally, there are two Foundation types that are especially important when reading and writing files in Swift - URL and Data. So this week, let’s take a closer look at various ways to use the many file system-related APIs that Swift offers - both on Apple’s own platforms, and on platforms like Linux - and a few things that can be good to keep in mind when working with those APIs. While many apps these days, especially on iOS, might not give users transparent access to open, save, and update documents as they please - whenever we’re dealing with some form of long-term data persistence, or a bundled resource, we always have to interact with the file system one way or another. Reading and writing files and folders is one of those tasks that almost every app needs to perform at some point.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |