swift编程NSErrorPointer错误等

Question

var data: NSDictionary = 
    NSJSONSerialization.JSONObjectWithData(responseData, options:NSJSONReadingOptions.AllowFragments, error: error) as NSDictionary;

这行代码给了我错误

NSError is not convertable to NSErrorPointer.

所以我想把代码更改为:

var data: NSDictionary =
     NSJSONSerialization.JSONObjectWithData(responseData, options:NSJSONReadingOptions.AllowFragments, error: &error) as NSDictionary;

这会将NSError错误转换为NSErrorPointer.但后来我得到一个新的错误,无法理解它:

NSError! is not a subtype of '@|value ST4'

Answer 1

自Swift 1以来,这些类型和方法发生了很大变化.

1. 该NS前缀被丢弃
2. 这些方法现在抛出异常而不是获取错误指针
3. 不鼓励使用NSDictionary.而是使用Swift字典

这导致以下代码:

do {
    let object = try JSONSerialization.jsonObject(
        with: responseData,
        options: .allowFragments)
    if let dictionary = object as? [String:Any] {
        // do something with the dictionary
    }
    else {
        print("Response data is not a dictionary")
    }
}
catch {
    print("Error parsing response data: \(error)")
}

如果您不关心特定的解析错误:

let object = try JSONSerialization.jsonObject(
    with: responseData,
    options: .allowFragments)
if let dictionary = object as? [String:Any] {
    // do something with the dictionary
}
else {
    print("Response data is not a dictionary")
}

原始答案

您的NSError必须定义为,Optional因为它可以是nil:

var error: NSError?

您还想要解释将在返回nil或解析返回数组的解析中出现错误.为此,我们可以使用as?运算符选项.

这给我们留下了完整的代码:

var possibleData = NSJSONSerialization.JSONObjectWithData(
    responseData,
    options:NSJSONReadingOptions.AllowFragments,
    error: &error
    ) as? NSDictionary;

if let actualError = error {
    println("An Error Occurred: \(actualError)")
}
else if let data = possibleData {
   // do something with the returned data
}

Answer 2

如上所述,错误必须定义为可选(https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/buildingcocoaapps/AdoptingCocoaDesignPatterns.html)

但是 - 如果出现错误并返回nil,此代码将崩溃,"As NSDictionary"将成为罪魁祸首:

var data: NSDictionary =
 NSJSONSerialization.JSONObjectWithData(responseData, options:NSJSONReadingOptions.AllowFragments, error: &error) as NSDictionary;

你需要像这样进行json解析:

var jsonError : NSError?

let jsonResult : AnyObject? = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &jsonError)

if let error = jsonError{
    println("error occurred: \(error.localizedDescription)")
}
else if let jsonDict = jsonResult as? NSDictionary{
    println("json is dictionary \(jsonDict)")
}
else if let jsonArray = jsonResult as? NSArray{
    println("json is an array: \(jsonArray)")
}

那可行.还记得json可以作为一个数组返回.您没有为选项传递nil,而是可以传递任何您喜欢的内容,例如:

NSJSONReadingOptions.AllowFragments

如果你喜欢.