swift - 'if (let keychain = KeychainService.loadToken())' 给我一个预期的声明错误

Question

我的应用程序崩溃了，因为它在展开时发现 nil:

var keyChain:String = KeychainService.loadToken()!

所以我尝试这样做:

if (let keyChain = KeychainService.loadToken()){

}

但它给了我错误:预期声明

这是正确的方法吗？如果不是我做错了什么？

如果您不想看到我的 KeychainService 类:

// Identifiers
let serviceIdentifier = "serviceIndentifier"
let userAccount = "userAccount"
let accessGroup = "accessGroup"

// Arguments for the keychain queries
let kSecClassValue = kSecClass as NSString
let kSecAttrAccountValue = kSecAttrAccount as NSString
let kSecValueDataValue = kSecValueData as NSString
let kSecClassGenericPasswordValue = kSecClassGenericPassword as NSString
let kSecAttrServiceValue = kSecAttrService as NSString
let kSecMatchLimitValue = kSecMatchLimit as NSString
let kSecReturnDataValue = kSecReturnData as NSString
let kSecMatchLimitOneValue = kSecMatchLimitOne as NSString

class KeychainService: NSObject {

/**
* Exposed methods to perform queries.
* Note: feel free to play around with the arguments
* for these if you want to be able to customise the
* service identifier, user accounts, access groups, etc.
*/
    internal class func saveToken(token: NSString) {
        self.save(serviceIdentifier, data: token)
    }

    internal class func loadToken() -> NSString? {
        var token = self.load(serviceIdentifier)

        return token
    }

    /**
    * Internal methods for querying the keychain.
    */
    private class func save(service: NSString, data: NSString) {
        var dataFromString: NSData = data.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!

        // Instantiate a new default keychain query
        var keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, userAccount, dataFromString], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecValueDataValue])

        // Delete any existing items
        SecItemDelete(keychainQuery as CFDictionaryRef)

        // Add the new keychain item
        var status: OSStatus = SecItemAdd(keychainQuery as CFDictionaryRef, nil)
    }

    private class func load(service: NSString) -> NSString? {
        // Instantiate a new default keychain query
        // Tell the query to return a result
        // Limit our results to one item
        var keychainQuery: NSMutableDictionary = NSMutableDictionary(objects: [kSecClassGenericPasswordValue, service, userAccount, kCFBooleanTrue, kSecMatchLimitOneValue], forKeys: [kSecClassValue, kSecAttrServiceValue, kSecAttrAccountValue, kSecReturnDataValue, kSecMatchLimitValue])

        var dataTypeRef :Unmanaged<AnyObject>?

        // Search for the keychain items
        let status: OSStatus = SecItemCopyMatching(keychainQuery, &dataTypeRef)

        let opaque = dataTypeRef?.toOpaque()

        var contentsOfKeychain: NSString?

        if let op = opaque? {
            let retrievedData = Unmanaged<NSData>.fromOpaque(op).takeUnretainedValue()

            // Convert the data retrieved from the keychain into a string
            contentsOfKeychain = NSString(data: retrievedData, encoding: NSUTF8StringEncoding)
        } else {
            println("Nothing was retrieved from the keychain. Status code \(status)")
        }

        return contentsOfKeychain
    }
}

Answer 1

省略大括号:

if let keyChain = KeychainService.loadToken() {
    ...
}