我是Swift,FMDB和一般开发的新手,我和我在运行时遇到致命错误:unexpectedly found nil while unwrapping an Optional Value.
错误发生在executeQuery
行
初步尝试和相关代码:
var rightAnswer:FMResultSet?
var memberDatabase:FMDatabase?
....
override func viewDidLoad() {
let path = NSBundle.mainBundle().pathForResource("1_celebs", ofType: "sqlite3")
memberDatabase = FMDatabase(path: path)
if memberDatabase!.open(){
print("database is ready")//it works if I comment out the stuff in loadquestion()
}
else{
print("error finding database")
}
...
func loadQuestion(){
let querySQL = "SELECT Quote, Answer, answerNumber, Celeb1, Celeb2, Celeb3, img1, img2, img3, feedbackImg, Context FROM celebs WHERE answeredRight = 'no' ORDER BY RANDOM() LIMIT 1"
rightAnswer = memberDatabase!.executeQuery(querySQL, withArgumentsInArray: queryParameters)
rightAnswer!.next()
然后我在func loadQuestion()
let results:FMResultSet? = memberDatabase!.executeQuery(querySQL, withArgumentsInArray: nil)
while(results?.next() == true)
{...}
然后我尝试了这个:
do{
rightAnswer = try memberDatabase!.executeQuery(querySQL, withArgumentsInArray: queryParameters)
while rightAnswer!.next(){...}
} catch let error as NSError {
print("failed: \(error.localizedDescription)")
}
然后,这个:
do{
let rs = try memberDatabase!.executeQuery(querySQL, values: nil)
while rs.next(){...}
} catch let error as NSError {
print("failed: \(error.localizedDescription)")
}
我每次在executeQuery
行都会收到相同的错误!如果我试图摆脱感叹号和问号,那么我在控制台上收到错误,说无法打开数据库。
答案 0 :(得分:2)
问题在于memberDatabase
是nil
。
您应该确保填充该变量。
另一个建议是,你应该避免强行解包操作员。它绕过编译器检查nil
(或可能的nil
)值。
Swift确实提供了更好的解决方案,比如
if let memberDatabase = memberDatabase {
try memberDatabase.executeQuery(querySQL, values: nil)
}
guard let memberDatabase = memberDatabase else { return }
try memberDatabase.executeQuery(querySQL, values: nil)