如何在iOS7兼容设备上使用UIAlertController（）作为全局变量？

Question

let alertControllerLoad = UIAlertController()
let alertViewLoad = UIAlertView()

These are both established as global variables in my inbox class. I check if the device is iOS8 or above before I call UIAlertController but since it creates an instance of the UIAlertController in the class it crashes on ios7 devices. I need them to be global variables since I call them from multiple functions. Is there a work around using init() or is this something that doesnt have a work around.

Answer 1

Unfortunately there are no preprocessor calls in Swift, Swift could be conditionally compiled based on the evaluation of build configurations in two functions only as of today.

os() for a choice of OSX or iOS and arch() for a choice of x86_64, arm, arm64 or i386.

So you can't use the Objective-C #if/#endif conditions for checking the iOS version.

But I think you can make a trick, as you do not need to know the exact iOS version, but only if UIAlertController exists. And you can check it in the following way:

if (objc_getClass("UIAlertController") == nil) {
   // iOS 7
} else {
   // iOS 8+
}

Then you do not need to have global references to either UIAlertController or UIAlertView but instantiate them locally from inside the if and call.

Answer 2

For anyone else that might stumble upon this,

class Alerts {

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
var iOS8Up: Bool = true

lazy var alertControllerLoad = Alerts.set()
let alertViewLoad = UIAlertView()


class func set() -> UIAlertController {

    //get the device model to know what image to post for refresh
    var device : UIDevice = UIDevice.currentDevice();
    var systemVersion = device.systemVersion;
    let numberFormatter = NSNumberFormatter()
    let systemVersionNumber = numberFormatter.numberFromString(systemVersion)
    let systemVersionFloatValue = systemVersionNumber!.floatValue

    if(systemVersionFloatValue < 8.0) {
        return UIAlertController(title: "title", message: "message", preferredStyle: UIAlertControllerStyle.Alert)
    }
    else{
        //returns with actionSheet as preferredStyle
        //will crash on anything less than iOS8
        return UIAlertController()
    }


}

}

this allows you to make a AlertController a global variable even if you're running iOS7. I spent far too long on this issue.