尝试从KeyChain获取价值时获取Optional（“”）

Question

当我尝试获取我的keyChain值时，它返回一个包含以下内容的字符串：

Optional("[thing in the KeyChain]")

因此，我尝试使用循环删除“可选”：

var str = KeychainService.loadToken()

for(var i = 0; i < 9 ; i++)
{
    str[i] = ""
}

但我得到一个错误：NSString没有名为“下标”的成员

KeychainService类：

import Foundation
import Security

let serviceIdentifier = "MySerivice"
let userAccount = "authenticatedUser"
let accessGroup = "MySerivice"

// Arguments for the keychain queries
let kSecClassValue = kSecClass.takeRetainedValue() as NSString
let kSecAttrAccountValue = kSecAttrAccount.takeRetainedValue() as NSString
let kSecValueDataValue = kSecValueData.takeRetainedValue() as NSString
let kSecClassGenericPasswordValue = kSecClassGenericPassword.takeRetainedValue() as NSString
let kSecAttrServiceValue = kSecAttrService.takeRetainedValue() as NSString
let kSecMatchLimitValue = kSecMatchLimit.takeRetainedValue() as NSString
let kSecReturnDataValue = kSecReturnData.takeRetainedValue() as NSString
let kSecMatchLimitOneValue = kSecMatchLimitOne.takeRetainedValue() 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) -> String? {
    // 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: String?

    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
    }
}

我只是不想删除str周围的Optional东西，还是有更好的方法呢？

我从以下代码中获取了代码：

http://matthewpalmer.net/blog/2014/06/21/example-ios-keychain-swift-save-
query/

Answer 1

Optional("")之所以得到，是因为未解开可选值。您需要!在对象后面放一个，您将再也不会得到它Optional("")了。我会向您显示代码，但您没有向我们显示该print()语句。我在下面做了一些示例，尽管我没有尝试过，但我认为可以重现此问题。

var value:String?
value = "Hello, World"

print("The Value Is \(value)") // Prints "The Value Is Optional(Hello, World)"
print("The Value Is \(value!)")// Prints "The Value Is Hello, World"

我希望这能回答您的问题，或者至少可以为您指明正确的方向，只是问您是否需要更多信息或更好的例子。