在Swift上捕获错误，并在View Controller上显示警告

Question

I am developing an application for IOS with Swift, and at some point run the line:

let myURLString = "http://FILE URL"
var myHTMLString:NSString = ""
if let myURL = NSURL(string: myURLString) {
    var error: NSError?
    myHTMLString = NSString(contentsOfURL: myURL, encoding: NSUTF8StringEncoding, error: &error)!

    if let error = error {
        var alert = UIAlertController(title: "Alert", message: "Message", preferredStyle: UIAlertControllerStyle.Alert)
        alert.addAction(UIAlertAction(title: "Click", style: UIAlertActionStyle.Default, handler: nil))
        println("Error : \(error)")
    }
    else {
        println("HTML : \(myHTMLString)")
    }
}
else {
    println("Error: \(myURLString) doesn't seem to be a valid URL")
}
return myHTMLString as String

This returns a String.

If the device (or the Mac while working with XCode) do not have Internet, the application fails because:

        myHTMLString = NSString(contentsOfURL: myURL, encoding: NSUTF8StringEncoding, error: &error)!

is null (nil)

My question is: How can I catch this error, execution continues, and display an error message in the View Controller?

Answer 1

Return myHTMLString as a String? optional instead of the String. Once the calling application gets back the myHTMLString variable, check for nil

    if let htmlString = myHTMLString{
         // HTML String returned by function isnt nil
    }
    else {
         // HTML String returned by function is nil. Handle the error
    }