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Hi guys.
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This is Angela from the app brewery.
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And before we get started digging in and building apps the first thing I want to talk about is how exactly
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does an app work.
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Because we'll have it in our phones we use it to do really important things like banking and contacting
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friends.
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But there are actually very few people who know just exactly how an app actually works.
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So let's start off by getting an overview of that.
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Now the first thing we have to realize is that smartphones are actually no different from just any other
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computer and an app is just code that we write to tell that mini computer what it should do.
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So let's say we have an app that just has a single button on it that says Click me when the user taps
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on the screen of that phone.
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Then the sensors in the phone register that tap and sends a message to the operating system which in
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the case of an iPhone would be iOS.
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Now the operating system then looks at the data that it gets from the sensor including things such as
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how much pressure was applied onto the phone at which location on the phone screen did it register that
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pressure and a whole bunch of different things and a whole lot of numbers.
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But the operating system takes all of those numbers and makes sense of it.
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And once it does then it will know that this particular button on the screen of this particular app
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was tapped at this time point and then he'll send a message to the app in question telling it that hey
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this button of yours got tapped.
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What should it do?
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And so the code that you write for your app should specify in this situation when the button called
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Click me gets tapped,
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this is what it should do.
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It should change what's shown on screen.
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And it should do this and that and that.
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So essentially as an app developer you're planning out all of the scenarios and what should happen.
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In each case was almost a bit like emergency planning if the building is on fire.
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What should happen.
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Well we should probably evacuate the staff and we should probably shut all the doors to prevent the
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fire from spreading.
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Well it's exactly the same for apps.
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What should happen when a user taps on this particular button?
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Well we should change the screen background to red.
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We should show them some other pieces of information and then we'll wait to see what the user does next.
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And then there's a plan for how to respond to the next event.
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So this essentially only three components to every single mobile app.
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There are the user interface elements that you see on screen, so those can be things such as buttons or
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images or toggles and sliders.
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And when we first build our app we're going to set up the screen.
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So we're going to drag on some buttons and place it in a location that we think makes sense and then
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add images or add other interface elements to the screen.
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Now when those elements get interacted with by the user say somebody taps on the button then we've got
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the second component of the app that comes into play which is the code and this code is the plan.
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If this button called click me gets tapped on, then what's the next thing that should happen?
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Well, it's step one do this. Step to do that. Step three do that.
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But if the user, say, used the slider then in our code there'll be a section that plans for what should
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happen when the user uses the slider.
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And finally most of the apps especially if it gets more complex will have data that's stored in the
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app.
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So for example let's say we have a contact management app right where we have all the phone numbers
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of all of your friends and colleagues. Well on the screen when the user taps on a button that says Show
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me Bob's phone number.
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Then that will send a message to our code and we check through all of those lines of code to see how
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we should respond when the user taps on that button and the code will go into the data and fetch the
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relevant piece of data.
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So in this case that's of course Bob's phone number.
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And then it's going to send it back onto the screen and display it on the screen so that the user now
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sees the telephone number of Bob.
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Now previously I mentioned that a smartphone is just like a small computer but there's still a few crucial
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differences.
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The first difference is that a laptop or desktop computer is usually plugged into the wall but a phone
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on the other hand is usually wireless.
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We usually keep it in our pocket and it's not always charging.
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It's also a lot smaller.
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So the battery gets depleted much faster compared to a laptop.
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Now a phone also has less processing power.
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So if you tried to play something that's really intensive on your phone say the latest Far Cry or if
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you try to run Photoshop on your phone then it's not going to be able to do it.
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Because it has less memory and less processing power than your computer.
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So because the phone has limited resources on all of these fronts then in order for a user to actually
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have a good time using their iPhone, then we have to manage those resources very frugally.
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So for example you can't just make an app that drains the user's power in five minutes or make an app
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that's so demanding on processing power that it's so slow and barely chugs along on the phone.
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So in all smartphones, there's always a manager -somebody to manage all of those resources.
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And that is of course the operating system.
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So it's iOS in our case that we need to worry about. And this manager is a little bit like the factory
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boss.
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It tells our app "Hey, you're about to come on screen now."
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"Get ready."
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"The user wants to see something from you."
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"Don't let me down". Or it might say "Hey! You're draining the battery way too much."
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"I'm going to have to shut you down" or "Hey you, little app, the user is getting a phone call right now"
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"and I'm going to have to switch you off."
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"Make sure you save their data before you go home."
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And this is what I think about every time I see my apps shuddering and shaking in fear.
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So previously we looked at the three components that make up any app namely the screen, the code, and
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the data.
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Well we actually have to zoom out a little bit and see the bigger picture which includes the role of
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the operating system.
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So when we think back to that plan that we're writing when we're coding up the apps, then that plan has
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to take into account all of the events that happen not just when a button inside the app is tapped or
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when the user shakes the phone when our app is open but also things such as when the operating system
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tells us that the user is getting a phone call.
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So our app is going to be switched into the background.
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So we have to also plan ahead for those situations.
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Well if the user is getting a phone call but they were midway through filling out a long form inside our
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app, we don't want them to come back after the call and realize all of that data has been lost.
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So we have to plan on how we save that data when a user gets a call for example.
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So all in all when we build an app we're essentially writing a very long and very extensive plan to
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plan for what should happen under lots of possible scenarios.
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And when the app is launched on the phone it looks to this plan to see what it should do.
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So, in the course we're going to be digging into every single aspect that we spoke about in this lesson
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and this is a little bit of a teaser of what's yet to come and what you're going to be learning about.
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So that by the end of the course you'll understand exactly how the app works and build any app that
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you dream of.