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iOS Build a Simple iPhone App with Swift 2.0 Getting Started with iOS Development Swift Recap Part 2

Posted by Abdijabar Mohamed
Abdijabar Mohamed
1,462 Points

Confused about how I should use switch and points together

//Where is the error in my code

class Machine {
    var location: Point

    init() {
        self.location = Point(x: 0, y: 0)
    }

    func move(direction: String) {
        print("Do nothing! I'm a machine!")
    }
}

// Enter your code below
class Robot: Machine {
override func move(direction: String) {
switch direction{
case "Up": y.Point = y+1
case "Down": y.Point = y-1
case "Left": x.Point = x-1
case "Righ": x.Point = x+1
default: break
        }
    }
}

THE QUESTION IS:

In the editor you've been provided with two classes - Point to represent a coordinate point and Machine. The machine has a move method that doesn't do anything because most machines are motionless.

Your task is to subclass Machine and create a new class named Robot. In the Robot class, override the move method and provide the following implementation. If you enter the string "Up" the y coordinate of the Robot's location increases by 1. "Down" decreases it by 1. If you enter "Left", the x coordinate of the location property decreases by 1 while "Right" increases it by 1.

Note: If you use a switch statement you can use the break statement in the default clause to exit the current iteration.

5 Answers

Steve Hunter
Steve Hunter
57,712 Points

Hi there,

You have a location variable that is of type Point. A Point has two properties, x and y. To access these properties, you access them from the instance variable, location. So, you can access the x position with location.x and the y position with location.y.

You have the correct implementation of the switch statement, i.e. you are adding and taking away from x and y appropriately, but you've not quite accessed them correctly. s above, you need to go through location to access each, not straight to the Point struct/class. Use the ++ and -- operators on each position to move the location.

Your code will look something like:

class Robot: Machine {
  override func move(direction: String){
        switch direction{
            case "Up" : location.y++
            case "Down" : location.y--
            case "Left" : location.x--
            case "Right" : location.x++
            default : break
        }
  }
}

I hope that helps.

Steve.

Steve Hunter
Steve Hunter
57,712 Points
Steve Hunter
Steve Hunter
57,712 Points

Change the parameter type going into the func - this works:

    func enum_move(direction: Direction){ // not an override - different parameter
        switch direction{
        case .Up : location.y++
        case .Down : location.y--
        case .Left : location.x--
        case .Right : location.x++
        }
    }

Tested and looks good! :-) If you're using this to pass the challenge, you'll need to rename the method else the tests will fail. I'll have a go to see if I can get it to pass now.

Steve.

Steve Hunter
Steve Hunter
57,712 Points

[EDIT] - Of course it won't pass the tests in the challenge as that is expecting to send a String "Up" to move the Robot, not an enum value. The enum method needs to be used such as:

let robot = Robot()
robot.move(Direction.Right)

That's not a string so the challenge tests using ...

robot.move("Up")

... will fail.

Steve.

Abdijabar Mohamed
Abdijabar Mohamed
1,462 Points
Abdijabar Mohamed
Abdijabar Mohamed
1,462 Points

Thanks Steve. I appreciate

Steve Hunter
Steve Hunter
57,712 Points

No problem - I hope it helped.

Steve.

Mitchell Warmerdam
Mitchell Warmerdam
4,225 Points
Mitchell Warmerdam
Mitchell Warmerdam
4,225 Points

Hi Steve,

Thanks for your answer.

However, I have one question. When I try to link the cases to the Enum "Direction", I get an error. Could you explain why this is not possible?

class Robot: Machine {
  override func move(direction: String){
        switch direction{
            case .Up : location.y++
            case .Down : location.y--
            case .Left : location.x--
            case .Right : location.x++
            default: break
        }
}
}

Thanks, Mitchell

Steve Hunter
Steve Hunter
57,712 Points

Hi Mitchell,

How have you implemented the Enum?

Steve.

Mitchell Warmerdam
Mitchell Warmerdam
4,225 Points

Hi Steve,

The Enum is implemented as followed

enum Direction { 
case Left 
case Right 
case Up 
case Down 
}

Cheers, Mitchell

Steve Hunter
Steve Hunter
57,712 Points

Apologies, I'm being slow today - been out running so the brain's a bit dead!

The func is expecting the user to call it by sending in a String as a parameter. How will the user call the func using your enum?

I'm just firing up Xcode (after the update has installed) and will have a go at finding a solution for you.

Steve.

Mitchell Warmerdam
Mitchell Warmerdam
4,225 Points

Thanks Steve. I understand that part now. However, I'm still struggling with completing the challenge. In Xcode I get no errors but in the challenge the following code is not approved:

class Point {
    var x: Int
    var y: Int

    init(x: Int, y: Int){
        self.x = x
        self.y = y
    }
}

enum Direction {
    case Left
    case Right
    case Up
    case Down
}

class Machine {
   var location: Point

   init() {
            self.location = Point(x: 0, y: 0)
        }

   func move(direction: String) {
            print("Do nothing! I'm a machine!")
        }
    }

class Robot: Machine {
    override func move(direction: String){
            switch direction{
            case "Up" : location.y++
            case "Down" : location.y--
            case "Left" : location.x--
            case "Right" : location.x++
            default : break
            }
        }
}

Hopefully you can help me with this last question ;)

Thanks, Mitchell

Steve Hunter
Steve Hunter
57,712 Points

Your code works fine for me here - there may be a temporary glitch in the compiler?

Steve.

Steve Hunter
Steve Hunter
57,712 Points

Mitchell,

The reason your code won't work is that there are two challenges that are essentially the same. One uses Strings, the other uses Enums.

This question was initially about the string implementation. This challenge.

You are trying to solve this challenge which uses Enums.

That code should look like:

    func move(direction: Direction) {
        // Enter your code below
        switch direction{
        case .Up:  location.y++
        case .Down:  location.y--
        case .Right:  location.x++
        case .Left:  location.x--
        }
    }

Apologies for the confuson - I only just saw the other challenge when another student asked about it. I went to link them to this post, but saw that the quiz was slightly different!!

Sorry for the confusion - I hope you go this sorted eventually. Luckily, my solution with the Enums would work, though.

Steve.

Dale Bailey
Dale Bailey
20,269 Points
Dale Bailey
Dale Bailey
20,269 Points

There is currently an error on treehouse where by you need to escape the ' in "Do nothing! I'm a machine!" like so "Do nothing! I\'m a machine!" This is the correct code

class Point {
    var x: Int
    var y: Int

    init(x: Int, y: Int){
        self.x = x
        self.y = y
    }
}


class Machine {
    var location: Point

    init() {
        self.location = Point(x: 0, y: 0)
    }

    func move(direction: String) {
        print("Do nothing! I\'m a machine!")
    }
}

// Enter your code below
class Robot: Machine {
    override func move(direction: String) {
        switch direction {
        case "Up": ++self.location.y
        case "Down": --self.location.y
        case "Left": --self.location.x
        case "Right": ++self.location.x
        default: break
        }
    }
}
Steve Hunter
Steve Hunter
57,712 Points

Hi Dale,

The escape character will restore the code formatting, ensuring the colours are consistent but the compiler/parser should still pass the correct code without escaping the apostrophe?

Steve.

Dale Bailey
Dale Bailey
20,269 Points

Yeah, Just thought it was worth mentioning as syntax highlighting quickly shows up any other errors users may be having