Exercise 1 - Simple UI

Fork and clone this repository and write a simple App with a couple of interface elements that does something useful. Regularly commit your changes and create a pull request when you are finished.

Implement one of the following examples or an idea of your own. I look forward to creative Apps!

Counter: The screen shows a label that displays the value of an attribute var count: Int when a method named updateLabel() is called. Buttons with titles "+1", "-1" and "Reset" change the value of count accordingly and call the updateLabel() method.
BMI: When you enter weight m and height l, the App calculates and displays the Body Mass Index BMI = m/l^2.
RGB: You can enter color values 0 to 255 for the red, green and blue components in three text fields. A button sets the background color self.view.backgroundColor accordingly and another button generates a random color. You can also add a UISwitch that toggles a repeating timer that changes the background color randomly at each interval (see hints below).

Hints:

We are going to learn the object oriented programming in Swift systematically in the next lecture. Try to manage this exercise with some intuition and the hints given here. Ask me for help by sending a pull request when you get stuck.

The attribute text of UILabel and UITextField return an optional String?. Use the optional binding syntax to unpack the optional:

 if let name = nameTextfield.text {
     // name exists and can be used here
 } else {
     // nameTextfield.text does not have a value
 }

You can quickly convert a String to a number using the Initializers Int() or Double(). This can fail, so again an optional is returned that you need to unpack:
```
 // text is a String
 if let number = Double(text) {
    // successfully converted text to a decimal number
 }
```

Define an attribute such as var count: Int with a default value:

 class ViewController: UIViewController {

     var count: Int = 0
 
 	// ...

 }

Of course Swift provides the basic calculation operators +-*/. These can be used in conjunction with setting a new value, e.g. to increase the value of a variable count by 1:
```
 count += 1
```
A color is represented by UIColor. The Initializer UIColor(red:green:blue:alpha:) accepts values from 0 to 1:
```
 let color = UIColor(red: 1, green: 0, blue: 0, alpha: 1) // red
```
The function arc4random_uniform(n) returns pseudo random numbers x with 0 <= x < n.

When a UISwitch is tapped by the user it emits an Event UIControlEvent.ValueChanged, very similar to a UIButton. With an attribute var: randomTimer: NSTimer? we can implement a method for randomly changing the background color:

 var randomTimer: NSTimer?

 @IBAction func switchValueChanged(sender: UISwitch) {
 	if sender.on {
 		randomTimer = NSTimer.scheduledTimerWithTimeInterval(0.15, target: self, selector: "randomButtonPressed:", userInfo: nil, repeats:true)
     } else {
         randomTimer?.invalidate()
         randomTimer = nil
 	}
 }

This periodically calls the method randomButtonPressed(_:) that must also be implemented.

lucasmllr/SimpleUI

Exercise 1 - Simple UI

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