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Save uniform default

hello and welcome back to another coach prayer tutorial in today's tutorial we are going to be learning all about user defaults we are going to learn what user defaults is when we should use it how to save values to it and how to read values from it we're also going to learn how to find where the property list is saved on a simulator or on an actual device so we have a full understanding of what's going on when we actually use user defaults in our application if you're new iOS developer just getting started make sure you check out my iOS development fundamentals course you can find links for that down below in the description it's a great course for beginners with over three hours of video tutorial content it'll teach you the fundamental skills that you need to know to become a great app developer if you sign up using my links you'll get the course for 50% off on you to meet or if you sign up with my skill share link you'll get two months of Skillshare premium for free so let's open up Xcode and get started alright so to illustrate this tutorial we're going to create a very basic screen and an app that looks like it would be a settings screen where you have some switches they can toggle on or off and some values are going to be saved based on the selection that the user in your app makes and so really we want to ask the question when should we use user defaults and user defaults is a great candidate for use when you have data or settings that you want to save that's not sensitive it's not personal identifiable information it doesn't need to be encrypted it's just dumb data for maybe some simple settings in your app like when should I show this screen or have I viewed something before and I don't need to see it again unless I delete the app so lots of instances and scenarios like that are great times when user defaults is just simple and easy to use and so we want to understand kind of where all that data goes when we use it so if we dive into a new iOS application here I've already gone ahead and just done some preliminary work for creating a settings screen it's just two switches and the text field and really this doesn't matter but I just want to simulate what this would look like in a real life scenario so if we head on over into the view controller we can take a look at what we need to do and I've gone ahead and hooked up some interface they're outlets here for the UI elements and assigned the delegate for the textfield and that's it so we're going to stub out these two functions here right to user defaults and read from user defaults so if you want to take a quick look at this you can go ahead and pause the video and get get set up and get caught up and then we'll go ahead and start implementing out these so we'll start off implementing the right to user defaults method first and the way we access user defaults is through the singleton so let's user defaults equals user defaults dot standard and let's command click into this so we can read up on the documentation here so when we take a look here we're inside of the class user defaults and this is the global instance of the user defaults configure to search the current applications search list and it's just simply this variable called standard that's basically the singleton and so that is what we're going to use most of the time here and user defaults is very key value pair oriented meaning we save values for given keys and we read values for the same keys and if they exist we can get the values from them and that's really the gist of how this works if you scroll down through the documentation in the API here you can see lots of things like remove object for a key a string for a key and array all these different data types can actually be saved and read from user to false which is really great so what we'll do is go back into our view controller here and actually start writing our values first okay so let's look at how we write the data so if we do user defaults dot seft you'll see that when we look back at the available methods we can use to persist a value for a key there's quite a few so they're set URL for a key set value any with any being an optional type for a key set the value of a bool for a key a double a float in hints and you get the idea so on and so forth so what's great is we can we can or literally pretty much anything and it can be nil so that's kind of how we're going to use this here is what we're going to do is do a set value and that value is going to be the input text vo text let me see if I can get my ex Co to work with me here there we go input text field text for a key now the key is gonna be the name the identifier that we want to use to save and write this value to so I'm just going to call mine input text it's probably good to move this to a constant and we can do that so what we'll do here is private let input text key equals input text and what we'll do here is replace that with the constant so I don't have to keep typing that over and over and so that's gonna write the text fields text into the property list for user defaults now we'll do the same thing for the switches user defaults that's set will use the bull for the key and so what we'll do here is we have two switches we have this clear cache switch dot is on for a key and we'll go ahead and do the same thing here private let clear cache key and we'll do clear cache here and for the final one we'll do the same thing use your default dot set refresh image switch that is on for a key that will hook up to a constant yeah well use that key to save that value the next place we have to determine is where do we want to execute this right to use or defaults method now since I'm using the UI text field delegate text field should return method basically any time I press the return key on the text field we're gonna go ahead and call this method here so what I'll do is right when we dismiss the text field keyboard will just call right to user default and that's gonna go ahead and persist whatever the values are for the switches and whatever text we have in the text field at that point in time so let's go ahead and run that now in the simulator and see what we get so it looks like my switches are on here and let's say I turn off this setting right so I was in the app and maybe there was some setting for clear cash on logout that was turned on I got to turn it off let's say I leave this one on and I just put some test text like that and we could hit return and so we've just gone ahead and wrote the values or written the value so user defaults but where do those actually go where do they live in the app and so that's the next piece of the puzzle that we're going to look at so to find the property list where we just saved those settings we need to actually figure out how to get to it so if you're on a simulator you kind of have to know the path for where the sandboxed application is saved relative to your simulator sometimes you don't know that off the top of your head it's kind of in a obscure location in the file directory so there's actually two tools we can use here one is called sim folders and it's a paid application but it makes it really easy to navigate to where the folders are in your iOS simulator and if you don't want to pay money for anything you can also use an open source one called open sim on github.com luo cheng open sim and i'm actually going to use this one for this tutorial and so what this tool does is if I open it here I can see my simulators that I have available and the green one shows my iPhone se is the one I have on and I can go right to my sandbox application and then I can go to reveal sandbox in finder and so what that does is that brings up the folder hierarchy of where the app is so now we need to find our property list so without us changing anything if we go into library then into preferences that's usually the general location where the property list is going to be saved so if we double-click this user default property list here you can see that there's three entry saved there is input text with the actual values that I wrote the clear cache key with the boolean set defaults or no and the Refresh image key with the value boolean set to true and you can see it's a dictionary like structure so there's three key value pairs in here and those correspond to each one of the entries that we wrote and like I said it's in a very obscure location so if you were to like take a terminal and just let me do something here well CD into that directory just so you can see where where it is you can see that's a you know library developer core simulator devices and then this long you know device name data containers you have to find all of this on your own if you don't use one of these kind of tools so that's why I recommend either open sim or sim folders or anything else if you even want to write your own from scratch just to make it a little bit easier if you have to test these things and obviously if you're on a real device then this isn't going to work it's going to be actually saved on the sandbox application on your actual device so that's just something to keep in mind okay so how do we read these back well it's quite simple we'll do the same thing in our read from user defaults method by using our user defaults singleton here and we'll do is input text field texts which you'll notice that's an optional string equals user defaults dot string for key and you'll notice that returns back an optional string the key is gonna be the exact same key we used to save it right so input text key now the keys have to match if the key that you read is different from the key that you're writing you may not get back any value at all or you may get back a value for a different key that you saved so if you want to load something that you saved you have to make sure that you are reading from the key that you wrote to it so on and so forth so if we go down here again clear cache switch thought is on it's going to equal the user defaults dot bool for key and that's going to be the clear cache key and we'll do the same thing for the refresh image switch like that and so all of our keys match up now let's say you didn't know the type right let's say you didn't know that it was a bool of straining well you can always do something like user default value for a key and let's say input text key and what you can do if you didn't know that maybe this value happens to be a string is you could you could cast it like this you know and do something like if let input text equals this as an optional string and then do something right but since we know that this is going to be a string value we can simply use string for key like we did here and avoid having to cast this as a string like we did here so that's just something to keep in mind so now let's go ahead and figure out where we want to call this obviously since we already wrote some values probably be a good idea to pop that into buted load right after everything's set now before we go ahead and run this code I want to talk about one more point sometimes it's important to know when you want to write or persist your values to user defaults if you go into app delegate you'll notice that there's life cycle methods here application more resign active did enter background will enter foreground so on and so forth well we can actually listen in for those notifications by subscribing for those notifications anywhere in our app so let's say for example we want to write our values when the app goes to the background what we can do is actually subscribe for this UI application did enter background notification inside of our table view controllers viewdidload method so if we actually command click here you can see that there's a whole slew of these notifications for the app lifecycle did enter background will enter foreground did finish launching we can know every state of our app and respond accordingly when these get triggered so how do we subscribe for these well it's quite simple what we'll end up doing is Notification Center dot default dot add observer the observer is going to be self or you can think of that as the table view controller because that is the view controller we're in when we are referring to self the selector is going to be the method that's going to be invoked right so in this instance is going to be table view controller dot write to user defaults the notification name is going to be exactly this because that was the name of the application lifecycle notification and for the object were just gonna pass in nil we're not going to do anything there and so right away we are now hooked into the lifecycle methods for when this fires and let me go ahead and correct this because I think I need to add at objc for my yeah right that's got to be Objective C friendly and this needs to be fixed to yuck notification that name that's fine I don't even throw in a print statement in here print writing to either defaults now like that and we can just keep an eye out for that in our console log here so let's go ahead and run this and let's see what we get it's right away we've got our switch turned on and our test text loaded so let's go ahead and start playing around with this so let's start off by turning switch off back rounding me up writing values to user defaults now that pencils getting fired come back in now of course it's still off but let's say we swipe kill the app writing the values user defaults again come back in the switch remains off now let's say I change the text to test text to background the app now it's not gonna print in the console because I've actually killed my Xcode from running here but if I swipe kill the app and we come back in test text to is persistent so if I turn both back on or let's just say I turn clear cache on logout set the true and then let's just say this test text two is set to the value of three and here and we background it because that's gonna fire the right method let's say we swipe kill the app I can get it there we go here test text three is what we read into the into the into the UI control and this switch is turned on and then if we go and really want to be a hundred percent certain here refresh my little simulator tool here sometimes sometimes it flakes out and I have to quit it and restart it here right user defaults tutorial reveal in sandbox it's good the library preferences and we can see side-by-side comparison that the clear cache has the value set to yes the Refresh image set to no I actually think these refresh in real-time here let me do switch that off ya see that switches in real-time it's kind of cool so if we do test text 4 you can actually see that being written to just like that and so yep okay so what if I wanted to completely remove one of these key value pairs from the property list well we can do that too so let's just say I wanted to completely blow away the input text key value pair what I can do here is let's say I go into my viewdidload and just immediately right before the read method here will just call user defaults standard user defaults dot remove object for a key and we'll just go ahead and give it the input text key here right so let's just throw a breakpoint here so we can see when it runs and we'll just do a little side by side of our property list so we've got our list open here and we'll run our simulator so they can keep my list open here and remove it and so you can see that we're all right our text is gone and if we go to our property list we only have the clear cache and the Refresh image keys saved because we completely removed the object for the given key so that's just something if you need her if you need to know how to remove them that's how you can do it you can use the API for removing object for a key and that's just fine so that's pretty much it user defaults is pretty simple to use obviously you can read you can write you can delete from it you can understand where the property list is where it lives on the filesystem and understand that you don't want to abuse it it's great for non sensitive client-side settings that you don't really care if you lose them they can be regenerated quite easily in the app you know and this is something where ok if you had to pull in something like core data or having to write to a text list or a text file or something like that well then the property lists using user defaults would probably be a great candidate for just a simple solution for anything that fits into that scenario and that wraps up this tutorial if you found this tutorial helpful let me know go ahead and smash that like button and consider subscribing the code Pro to stay up to date for all the latest tutorials make sure you follow code pro on social media you can find me on Facebook on Twitter Skillshare you to meet in patreon and let me know in the comment section down below if you found this helpful and what tutorials you guys would like to see next thank you so much for stopping by and I'll catch you in the next one [Music] you