将NSData初始化为nil SWIFT

Question

How can I init NSData to nil ?

Because later, I need to check if this data is empty before using UIImageJPEGRepresentation.

Something like :

if data == nil {
    data = UIImageJPEGRepresentation(image, 1)
}

I tried data.length == 0 but I don't know why, data.length isn't equal to 0 while I haven't initialized.

Answer 1

One thing you can do is ensure your NSData property is an optional. If the NSData object has not been initialized yet, then you can perform your if nil check.

It would look like this:

var data: NSData? = nil
if data == nil {
    data = UIImageJPEGRepresentation(image, 1)
}

Because optionals in Swift are set to nil by default, you don't even need the initial assignment portion! You can simply do this:

var data: NSData? //No need for "= nil" here.
if data == nil {
    data = UIImageJPEGRepresentation(image, 1)
}

Answer 2

If you want a nil NSData , then you can initialize it like this:

var data: NSData?

Then you can use:

if data == nil {
    data = UIImageJPEGRepresentation(image, 1)
}

If you are wanting empty data, then initialize it like this:

var data = NSData()

And to check that it is empty:

if data.length == 0 {
    data = UIImageJPEGRepresentation(image, 1)
}

Answer 3

If you want to set your data variable to nil , just do data = nil . If you want to set it to be empty, then do data = NSData() .