Swift - Cannot use += operator with String! from UITextField or UITextArea - Implicitly Unwrapped Optional

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I'm guessing this is a bug (submitted bug #19223563, but if it isn't, you'll be surprised to learn that in Xcode Version 6.1.1 you cannot append to a String from a UITextView or UITextField.

The problem is that both the UITextField and the UITextView are using an implicitly unwrapped optional String (String!) as the type. This is messing up the +=, so you either have to break apart the statement (defeating the purpose of +=). Or you have do a force unwrap before the +=.

If you don't you'll get a strange Swift Compiler Error stating that 'String!' is not identical to 'UInt8'

var numberString: String! = "0"
numberString = numberString + "2"

numberString! += "1"
numberString += "1" //'String!' is not identical to 'UInt8'

var textView = UITextView()
textView.text += "More text" //'String!' is not identical to 'UInt8'

var textField = UITextField()
textField.text += "Even more text" //'String!' is not identical to 'UInt8'

WatchKit Swift Tutorial - Download Xcode 6.2 Beta and Start Making Apple Watch Apps

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The first beta of the WatchKit SDK was launched this past week and developers can now start making apps.

There are some limitations, but Apple released a lot more than was expected for WatchKit. There's a lot you'll be able to do within the restrictions, which are related to the embedded hardware (i.e.: Apple Watch) and it's battery life.

For now, until Native Apple Watch support is added sometime next year (fingers crossed), you'll have to work within the provided mechanisms. If something doesn't work, you'll need to let Apple know by submitting bug reports, feature requests, or enhancements to WatchKit or Xcode.

Known Limitations of WatchKit in Xcode 6.2 Beta

  1. Updated: (Beta 2 allows Watch apps to trigger iPhone apps) You cannot press a button on Apple Watch to cause an action in your iPhone app.
  2. You cannot create or use gestures. All gestures are controlled by Apple.
  3. You cannot move objects around screen by CGPoint position (Maybe with tableview hide/show).
  4. You cannot add UI elements at run-time, everything is design time before app runs.
  5. You cannot make fluid 2D/3D games like Flappy birds (Maybe jittery gameplay with image animations + hiding/showing hackery, + borderless button).
  6. Animations are image-based (in Apple's sample they include 360 images to show a full circle progress bar = 2mb image data).
  7. Your code runs on your iPhone app in an extension (new in iOS 8), and your UI + images reside on the Apple Watch.
  8. Your app will stop if the Apple Watch and iPhone are separated beyond the range of bluetooth. Only Apple can run native apps on device.
  9. You can only use storyboard files for UI (no .xib files).
  10. You must create an iPhone app Xcode project and add Apple Watch targets to create an app.
  11. You cannot use a physical iPhone with the Apple Watch simulator. Only available in simulation on Mac.

With some of the limitations in perspective, you can design apps that provide meaningful information that compliment your iPhone app. The watch is intended to show information that can be used quickly, and it isn't designed as a gaming device because of it's limited battery and processing power.

Download and install Xcode 6.2 Beta from the Apple Developer Website

Go to https://developer.apple.com/watchkit/ and you can download the beta versions of Xcode 6.2 and iOS 8.2 for testing out features relating to Apple Watch.

Scroll down to the bottom and read both the Apple Watch Design Guide and the Apple Watch Programming Guide.

Download Xcode 6.2 Beta using this link.

Getting Started with WatchKit in Xcode 6.2 Beta

In order to bring you up to speed, I've created a short YouTube video series in 4K resolution that demonstrates how to create a WatchKit app using timers. There are some bugs, but this is the best place to start if you want to work with some cutting edge technology.

Please submit any bug reports to http://bugreport.apple.com and you can help Apple improve WatchKit. Duplicate bug requests are a good thing, because it helps Apple see the more common issues.

Download the Xcode project with the Apple Watch app from github.

Swift WatchKit Tutorial 1 - Get Started with WatchKit to Make apps for the Apple Watch

WatchKit Swift Tutorial 2 - Getting Started with your First WatchKit App in Xcode 6 2 Beta

WatchKit Swift Tutorial 3 - Apple Watch User Interface Explained

WatchKit Swift Tutorial 4 - Connect the Apple Watch User Interface to Code

WatchKit Swift Tutorial 5 - Setup a NSTimer in Swift with Apple Watch

WatchKit Swift Tutorial 6 - Synchronize NSTimer and WKInterfaceTimer

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Parsing Int Variables in Swift - Optionals and Approaches

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Working with integer numbers in Swift is a little different, since the only string parsing method is toInt() and it returns an optional Int? value.

This means that you have to test the value before you use it, or it could be nil. Doing a force unwrap can result in a crash if you try to use the value.

Below are two approaches you can leverage using the if/else statements.

Approach 1

if let width = widthTextField.text.toInt() {
    if let height = heightTextField.text.toInt() {
        // Valid user input parsed
        println("Valid width: \(width), height: \(height)")
    }
}

Approach 2

var width = widthTextField.text.toInt()
var height = heightTextField.text.toInt()

if(width != nil && height != nil) {
    // Valid user input parsed
    println("Valid width: \(width!), height: \(height!)")
}

The benefit of the second approach is that you can test multiple optionals in a single line. You don't have to nest tons of if/else statements to make sure the values are valid.

I'd like there to be a better approach, but these are the two that I discovered from playing around with optionals. It would be nice if I could use the tuple syntax from a switch statement with the if let keyword.

Double Approach

Working with Double parsing is a different story. It doesn't look like their is a method on String, so you have to cast it to an NSString to convert. Going down that route you lose the Optional values. Invalid casts will return 0.

var width = (widthTextField.text as NSString).doubleValue

A Better Double Approach

The above code doesn't fail elegantly with optional values, and instead may give strange results. Use the NSNumberFormatter and get the double value from the NSNumber object it creates.

var numberFormatter = NSNumberFormatter()
var userInputString = "10.33a0" // 10.33
if let number = numberFormatter.numberFromString(userInputString)?.doubleValue {
    println("Converted user input: \(number)")
} else {
    println("Invalid number: \(userInputString)")
}


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