How to check object is nil or not in swift?

Question

Suppose I have String like :

var abc : NSString = \"ABC\"

and I want to check that it is nil or not and for that I try :

if         


        

Answer 1

Swift 4.2

func isValid(_ object:AnyObject!) -> Bool
{
    if let _:AnyObject = object
    {
        return true
    }

    return false
}

Usage

if isValid(selectedPost)
{
    savePost()
}

Answer 2

The null check is really done nice with guard keyword in swift. It improves the code readability and the scope of the variables are still available after the nil checks if you want to use them.

func setXYX -> Void{

     guard a != nil  else {
        return;
    }

    guard  b != nil else {
        return;
    }

    print (" a and b is not null");
}

Answer 3

Normally, I just want to know if the object is nil or not.

So i use this function that just returns true when the object entered is valid and false when its not.

func isNotNil(someObject: Any?) -> Bool {
        if someObject is String {
            if (someObject as? String) != nil {
                return true
            }else {
                return false
            }
        }else if someObject is Array<Any> {
            if (someObject as? Array<Any>) != nil {
                return true
            }else {
                return false
            }
        }else if someObject is Dictionary<AnyHashable, Any> {
            if (someObject as? Dictionary<String, Any>) != nil {
                return true
            }else {
                return false
            }
        }else if someObject is Data {
            if (someObject as? Data) != nil {
                return true
            }else {
                return false
            }
        }else if someObject is NSNumber {
            if (someObject as? NSNumber) != nil{
                return true
            }else {
                return false
            }
        }else if someObject is UIImage {
            if (someObject as? UIImage) != nil {
                return true
            }else {
                return false
            }
        }
        return false
 }

Answer 4

If abc is an optional, then the usual way to do this would be to attempt to unwrap it in an if statement:

if let variableName = abc { // If casting, use, eg, if let var = abc as? NSString
    // variableName will be abc, unwrapped
} else {
    // abc is nil
}

---

However, to answer your actual question, your problem is that you're typing the variable such that it can never be optional.

Remember that in Swift, nil is a value which can only apply to optionals.

Since you've declared your variable as:

var abc: NSString ...

it is not optional, and cannot be nil.

Try declaring it as:

var abc: NSString? ...

or alternatively letting the compiler infer the type.

Answer 5

if (MyUnknownClassOrType is nil) {
    println("No class or object to see here")
}

Apple also recommends that you use this to check for depreciated and removed classes from previous frameworks.

Here's an exact quote from a developer at Apple:

Yes. If the currently running OS doesn’t implement the class then the class method will return nil.

Hope this helps :)

Answer 6

func isObjectValid(someObject: Any?) -> Any? {
    if someObject is String {
        if let someObject = someObject as? String {
            return someObject
        }else {
            return ""
        }
    }else if someObject is Array<Any> {
        if let someObject = someObject as? Array<Any> {
            return someObject
        }else {
            return []
        }
    }else if someObject is Dictionary<AnyHashable, Any> {
        if let someObject = someObject as? Dictionary<String, Any> {
            return someObject
        }else {
            return [:]
        }
    }else if someObject is Data {
        if let someObject = someObject as? Data {
            return someObject
        }else {
            return Data()
        }
    }else if someObject is NSNumber {
        if let someObject = someObject as? NSNumber{
            return someObject
        }else {
            return NSNumber.init(booleanLiteral: false)
        }
    }else if someObject is UIImage {
        if let someObject = someObject as? UIImage {
            return someObject
        }else {
            return UIImage()
        }
    }
    else {
        return "InValid Object"
    }
}

This function checks any kind of object and return's default value of the kind of object, if object is invalid.