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iOS Build a Simple iPhone App with Swift 2.0 Structs as Data Models Finishing Up Our Model

Posted by roohart
roohart
5,529 Points

Help needed to understand the getRandomFact method

struct FactModel {
    let facts = ["Ants stretch when they wake up in the morning.",
        "Ostriches can run faster than horses.",
        "Olympic gold medals are actually made mostly of silver.",
        "You are born with 300 bones; by the time you are an adult you will have 206.",
        "It takes about 8 minutes for light from the Sun to reach Earth.",
        "Some bamboo plants can grow almost a meter in just one day.",
        "The state of Florida is bigger than England.",
        "Some penguins can leap 2-3 meters out of the water.",
        "On average, it takes 66 days to form a new habit.",
        "Mammoths still walked the Earth when the Great Pyramid was being built."]

    func getRandomFact() -> String {
        let randomNumber = GKRandomSource.sharedRandom().nextIntWithUpperBound(facts.count)
        return facts[randomNumber]
    }
}

I'm having a hard time understanding what is happening here. First of all; why is the return type of the function a string? Shouldn't it be like... an array? We are returning the facts array, right? Then; I'm not even going to go deeper in to the whole GKRandomSource -nightmare over there, but the "return facts[randomNumber] is just not clicking with me. Maybe another example of a similar situation would help?

Thaanks!

2 Answers

Philip G
Philip G
14,600 Points

Hi there,

let facts = ["Ants stretch when they wake up in the morning.",
        "Ostriches can run faster than horses.",
        "Olympic gold medals are actually made mostly of silver.",
        "You are born with 300 bones; by the time you are an adult you will have 206.",
        "It takes about 8 minutes for light from the Sun to reach Earth.",
        "Some bamboo plants can grow almost a meter in just one day.",
        "The state of Florida is bigger than England.",
        "Some penguins can leap 2-3 meters out of the water.",
        "On average, it takes 66 days to form a new habit.",
        "Mammoths still walked the Earth when the Great Pyramid was being built."]

Think of the facts array like a container that contains the Fact-Strings. 

let randomNumber = GKRandomSource.sharedRandom().nextIntWithUpperBound(facts.count)

The getRandomFact() Method first generates a random number which is smaller than the number of Strings in the array (because array indexes start at zero).

return facts[randomNumber]

Then, from the array, it returns the Fact-String at the index of the randomly generated number.

Hope I could help! If there's anything you don't understand, don't hesitate to ask me again :)

Best Regards,

Philip

roohart
roohart
5,529 Points

I stepped away from the computer for a while and came back to this step by step answer and I'm so grateful. Thank You! Makes sense now :)

Caleb Kleveter
MOD
Caleb Kleveter
Treehouse Moderator 37,862 Points
Caleb Kleveter
Caleb Kleveter
Treehouse Moderator 37,862 Points

Simple really once you under stand it. with this code:

let randomNumber = GKRandomSource.sharedRandom().nextIntWithUpperBound(facts.count)

you are randomly getting a number in a range from 0 to the upper bound of the array index in facts array. In other words, I have 0 through the highest number in the array index, I close my eyes and grab one, that is my randomly selected number. I then find the string that matches the index number and put it in the randomNumber variable box. I then return the variable box that has one string form the array. If you did return the array you would get an error because you can only assign a string, not an array, to a labels text property.

Hope this makes sense!

roohart
roohart
5,529 Points

THANK YOU! :) You cleared up the method for me!