How to assign an array element which can be null in Swift?

Question

In my Swift app, I'm querying an api returning a json object like this :

{
    key1: value1,
    key2: value2,
    array : [
        {
            id: 1,
            string: "foobar"
        },
        {
            id: 2,
            string: "foobar"
        }
    ]
}

Facts :

The array value can be empty.
I want to read the first array element, present or not.

In Swift i'm doing :

  if let myArray: NSArray = data["array"] as? NSArray {
      if let element: NSDictionary = myArray[0] as? NSDictionary {
          if let string: NSString = element["string"] as? NSString {
              // i should finally be able to do smth here,
              // after all this crazy ifs wrapping
          }
      }
  }

It works if the array and the first element exist, but i'm having a crash with "index 0 beyond bounds for empty array" even if the element assignment is within an if let wrapping.

What i am doing wrong here ? I'm getting crazy with Swift optionals, typing and crazy if let wrapping everywhere...

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

The error is not concerning about Optional. If you use subscription([]) for array, you have to check the length of that.

if let myArray: NSArray = data["array"] as? NSArray {
    if myArray.count > 0 { // <- HERE
        if let element: NSDictionary = myArray[0] as? NSDictionary {
            if let string: NSString = element["string"] as? NSString {
                println(string)
            }
        }
    }
}

But we have handy .firstObject property

The first object in the array. (read-only)

If the array is empty, returns nil.

Using this:

if let myArray: NSArray = data["array"] as? NSArray {
    if let element: NSDictionary = myArray.firstObject as? NSDictionary {
        if let string: NSString = element["string"] as? NSString {
            println(string)
        }
    }
}

And, we can use "Optional Chaining" syntax:

if let str = (data["array"]?.firstObject)?["string"] as? NSString {
    println(str)
}

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Feb 2, 2015 at 12:25

rintaro

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1 Comment

Sylver Over a year ago

I was having difficulties to understand all of that. This answer is well detailed and clear. Thanks, it helps me a lot.

qwerty_so · Accepted Answer · 2015-02-02 12:17:51Z

1

You can use this

var a = [Any?]()
a.append(nil)

If you have a non-optional array with AnyObject you can use NSNull (like in Obj-C)

answered Feb 2, 2015 at 12:17

qwerty_so

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