展开一个可选值Swift

Question

I am to load html file in my webview. The files contain references to /css and /images sub directories. So, I found the following from this answer .

    let path: String? = NSBundle.mainBundle().pathForResource("Ace-VetBolus", ofType: "html", inDirectory: "HTMLFiles")
    let requestURL = NSURL(string:path!);
    let request = NSURLRequest(URL:requestURL!);

    web1.loadRequest(request)

And I cannot resolve this issue: fatal error: unexpectedly found nil while unwrapping an Optional value at the second line.

Answer 1

Using ! forcefully unwraps a value, so if it's nil , you're going to get a fatal error as you see.

You want to use an if let statement or a guard statement.

let path: String? = NSBundle.mainBundle().pathForResource("Ace-VetBolus", ofType: "html", inDirectory: "HTMLFiles")
if let unwrappedPath = path {
    let requestURL = NSURL(string: unwrappedPath)
    let request = NSURLRequest(URL: requestURL)

    web1.loadRequest(request)
}

Using guard in Swift 2 functions like so:

let path: String? = NSBundle.mainBundle().pathForResource("Ace-VetBolus", ofType: "html", inDirectory: "HTMLFiles")
guard let unwrappedPath = path else {
    return // or handle fail case some other way
}
let requestURL = NSURL(string: unwrappedPath)
let request = NSURLRequest(URL: requestURL)
web1.loadRequest(request)

Biggest different is the guard pattern allows you to keep the unwrapped variable in the same scope, while if let creates a new scope.

Answer 2

You should use NSBundle method URLForResource:

if let url = NSBundle.mainBundle().URLForResource("Ace-VetBolus", withExtension: "html", subdirectory: "HTMLFiles") {
    let requestURL = NSURLRequest(URL: url)
    web1.loadRequest(requestURL)
}