Bob Lee Course Part 11 (lectures 19 to 20)

Schoo inspection is over! This thankfully means that I will have more time to code in the coming weeks. Last time I focused on computed properties including get/set. Now not all of that worked before. Never mind. Anyway, we're starting now with 'property observers' - getSet and willSet. Let's go!

Property Observers

Start Time - 15:04





So that is the difference between willSet and didSet. Interesting.

var myGrade: Int = 80 {
    willSet {
        print("Hey something happened!")
    }
    didSet {
        print("Hey something else happened!")
    }
}


myGrade = 100

Simple enough but once again my playground seems to be using the same error message of the code not compiling....

Paused at 15:09...

Right I am doing the update on Xcode - we will see if that helps! It could be the mac needs an update too...Anyway, I'm going to crack on just by looking at Bob's video without actually coding!

Restart at 15:11!

You can use 'newValue' again - that's an automatic constant that is provided by the Swift language. 

oldValue - this refers to the previous value basically. So 80 in the case below. 

So I guess the point of the property observers are to give warnings when a value is about to (willSet) and has (didSet) changed!

Again, like computed properties, you can specify the names of the values e.g. oldGrade/newGrade or whatever you want. 















So with this you can see the specific values put in with willSet(newGrade) and didSet(oldGrade). OK fine so far.

You can use if statements to make the didSet more specific:



















Paused at 15:25

 Restarted at 21:17

 So plenty of hours in between but I'm picking this back up with an updated Xcode. Let's see if that works....!

Paused again while another update goes on!

 Restart at 21:28

 So the next question is what application is there for property observers? Well Bob explains a login example.

var loggedIn: Bool = false {
    willSet {
        print("The user has tried something")
    }
    didSet {
        if loggedIn {
            print("The user has switched from \(oldValue) to \(loggedIn)")
        }
        
    }

}

So again, the willSet print line prints out to the console first, then the didSet print line will come up. 

There are lots of other real life applications with this - background colour, pop ups, password changes etc. All sorts of things basically!

So how are property observers different to computed properties? 


So it is about being OBSERVED that's the key thing here. The will/did set do not get called until the value is actually changed. TRACKING DATA - used with PO. 

Failable Init

Right so a recap first with using enum to create custom errors. Then using the throw keyword instead of the return symbol. 




















So in the above, the init uses 'throws' and then what error type, depending if the name is empty or not. 

Then error testing can be used....

class Blog {
    
    let name: String
    init?(name: String) {
        if name.isEmpty {
            return nil
        }
            self.name = name
        }
    }

let newBlog = Blog(name: "")

So newBlog is of optional type. 

if let blogName == newBlog.name {
    print(blogName)
} else {
    print("There is no name")
}

Now that did not work. It's to do with it being failable - i.e. no value...

if let blog = newBlog {
    print(blog)
} else {
    print("No value")
}

OK even better - 

if let blog = newBlog {
    print(newBlog?.name)
} else {
    print("No value")
}

The issue with this is that the value is not unwrapped yet. 

Stopped at 22:04 (total today - 54 minutes)

Well, some good stuff here. Stuff which I will need to go over. Property Observers were not new but there role has been clarified for me - tracking data basically. And as for failable init, well I'm not sure as to the advantage of designing purpose built error handling code. 

As this has been four courses now since a consolidation, I think I need one of these before moving on. Those consolidation sessions are where I really understand it on a deeper level and have the chance to 'OWN IT'. Then it will be four more courses before I finish this chapter. 

Another good thing with this course is that it is at a higher, more complex level than anything I have gone through AND stuck to. Usually by now I would have given up! But I'm keeping up with this, even though I do need to pause, think, stop and check more often. That's fine though - I could spend several more months on this course!

Looking at the longer game, after this course I have another Intermediate one lined up - from 'Sandra'. Anyway, the ULTIMATE aim is not to do as many Udemy courses as possible, but to actually start branching in to app development. I will review that after I've completed all of Bob's course! 

Comments

Post a Comment

Popular posts from this blog

*Xcode Project Entry 2* F1 Quiz - part 1

Image
It's Christmas Eve and time to code! To think, a year ago, I was plodding along with some eBook, blindly convincing myself that I was on a steady road to coding greatness. Really, it was from June where I made the decision to start again, humbling as that may seem. It would have been comforting to have completed endless 'beginner' courses but branching out and applying the theory is the key thing, which brings us to this entry. Yes, my second Xcode OWN project! I thought about doing an educational one, as there is certainly a lot of scope and relevance for that, being a teacher and all. However, making a quiz makes sense, for various reasons.  First off, I have made this before through Angela's excellent tutorial. No offence to Sandra, but hers is not even close to the elegance and effectiveness of Angela's project. The one thing to take from Sandra is the stack views. Definitely something I will use from now on. This is one of the great things about learning from...
Read more

Angela Yu Course Part 10 (up to lesson 112)

Image
It's unlikely that I'll be able to do any Swift tomorrow as I'm going to Eastbourne today, for the weekend. So I can give half an hour now, maximum! Coding Challenge - Destini App! Choose your own adventure books! I used to ADORE these. Angela explains that these have had some sort of revival through the Lifeline games. It's very binary - yes/no mostly. I have my own experience of this based on WDC... Now the challenge is to complete the game! Having followed the first few instructions, which I found a bit confusing it must be said, I was about to surrender and see the answer. Then I managed to stop myself - I CAN do this, or at least have a good go! Even if I don't get the correct answer, it will be good practice to put what I know into practice. This is my weakness, which I keep coming back to - that when some problem solving is required, I fold far too quickly. So here is what I need to do: Let's break this down... I need to use the...
Read more

Angela Yu Xcode 12 Course - Part 7 (lectures 74 to 79)

Image
No time to waste! Only got a short amount of time now so going to get a few minutes or so in! Start Time - 20:14 Conditionals If statement for 'love calculator' example. So a simple example for this. The idea will be that conditionals are used to show that the print statement will do it differently for whatever the number is. With updated Swift, I would use the Int.random(0...100). Easy fix that would be. Also no UIInt32 needed but just an Int. So with the if statements, it would be a STRING being returned.   Linked to the whole choose your own adventure - if/else for each choice. BMI Challenge No need to do this - easy enough to be honest. Just skimming through. BODMAS principles... So something I picked up on before is not needing the greater than AND less than value for the middle line (for the else if bmi > 18.5) A better solution, which Angela is already explaining before I could say it is returning a string instead of a Double. So the...
Read more