ios - Swift 中的可选类型错误 : fatal error: unexpectedly found nil while unwrapping an Optional value

Question

我正在尝试使用 FBSDK v4.x 从 facebook 获取相册。我使用下面的代码，在打印出来后得到 json 格式的结果，但随后它会导致如下错误: ' fatal error :在解包可选值时意外发现 nil'这一行:let graphData = result.valueForKey("data") as! [FBSDKShareAPI] .所以任何人都可以帮我解决这个错误。提前致谢。

func fetchAlbum(){
    print(FBSDKAccessToken.currentAccessToken())
    let graphRequest: FBSDKGraphRequest = FBSDKGraphRequest(graphPath: "me?fields=albums", parameters: nil);
    graphRequest.startWithCompletionHandler({ (connection, result, error) -> Void in
        if let gotError = error{
            print(gotError.description);
        }
        else{
            print("fetched data: \(result)")
            if result != nil{ 
            let graphData = result.valueForKey("data") as! [FBSDKShareAPI]  
            var albums:[AlbumModel] =  [AlbumModel]();
            for obj:FBSDKShareAPI in graphData{
                let desc = obj.description;
                println(desc);
                let name = obj.valueForKey("name") as! String;
                println(name);
                if(name == "ETC"){
                    let test="";
                }
                let id = obj.valueForKey("id") as! String;
                var cover = "";
                if let existsCoverPhoto : AnyObject = obj.valueForKey("cover_photo"){
                    let coverLink = existsCoverPhoto as! String;
                    cover = "/\(coverLink)/photos";
                }
                //println(coverLink);
                let link = "/\(id)/photos";
                let model = AlbumModel(name: name, link: link, cover:cover);
                albums.append(model);
                }
            NSNotificationCenter.defaultCenter().postNotificationName("albumNotification", object: nil, userInfo: ["data":albums]);

            }
        }

    })
}

Answer 1

更好的是，你可以走

if let graphData = result?.valueForKey("data") as? [FBSDKShareAPI] {
    //bla
}

它应该为你做所有的 nil 检查