Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

The first thing I would do is change the jsonResult variable to something else, such as jsonData.

if let jsonData = jsonResult {
    let weather_array = jsonData["weather"] as! NSArray
    // Rest of code here
}

The second thing I would do is set a breakpoint on the let weather_array line of code. Xcode will pause your app when it reaches that line of code. When the breakpoint is hit, type the following in the debug console:

po jsonData["weather"]

The value of the weather data will appear in the console. The probable cause of your crash is that the weather data is not an array. In your code, you are using as! NSArray to convert the json data to NSArray. The app is unable to make this conversion so the app crashes.

The following articles provide more detailed information on Xcode's debugger and Swift optionals:

• An Introduction to Xcode's Debugger
• Crashing with Swift Optionals

From the swift docs:

The nil-coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that’s stored inside a.

The nil-coalescing operator is shorthand for the code below:

1. a != nil ? a! : b

The code above uses the ternary conditional operator and forced unwrapping (a!) to access the value wrapped inside a when a isn’t nil, and to return b

otherwise. The nil-coalescing operator provides a more elegant way to

encapsulate this conditional checking and unwrapping in a concise and

readable form.

Note

If the value of a is non-nil, the value of b isn’t evaluated. This is known as short-circuit evaluation.

The example below uses the nil-coalescing operator to choose between a

default color name and an optional user-defined color name:

1. let defaultColorName = "red"
2. var userDefinedColorName: String? // defaults to nil
3. 
   
4. var colorNameToUse = userDefinedColorName ?? defaultColorName
5. // userDefinedColorName is nil, so colorNameToUse is set to the default of "red"

Don't use the "!" operator. The whole point of Swift is to be a "safe" programming language. In theory, it is so much better than C because C lets you do dangerous things. Well, so does Swift. If you don't know how and when it is safe to use those dangerous operators, then don't use them.