我是Swift的新手，我在从JSON文件中过滤NULL值并将其设置为Dictionary时遇到问题。我从服务器获取空值的JSON响应，它崩溃了我的应用程序。
这是JSON响应：
"FirstName": "Anvar",
"LastName": "Azizov",
"Website": null,
"About": null,
我将非常感谢您的帮助来处理它。
UPD1：此时我决定以下一个方式做到这一点：
if let jsonResult = responseObject as? [String: AnyObject] {
var jsonCleanDictionary = [String: AnyObject]()
for (key, value) in enumerate(jsonResult) {
if !(value.1 is NSNull) {
jsonCleanDictionary[value.0] = value.1
}
}
}
您可以创建一个包含相应值为nil的键的数组：
let keysToRemove = dict.keys.array.filter { dict[$0]! == nil }
然后循环遍历该数组的所有元素并从字典中删除键：
for key in keysToRemove {
dict.removeValueForKey(key)
}
更新2017.01.17
正如评论中所解释的那样，力展开算子虽然安全，但有点难看。可能有其他几种方法可以实现相同的结果，同一方法的更好看方式是：
let keysToRemove = dict.keys.filter {
guard let value = dict[$0] else { return false }
return value == nil
}
您可以通过以下函数将空值替换为空字符串。
func removeNullFromDict (dict : NSMutableDictionary) -> NSMutableDictionary
{
let dic = dict;
for (key, value) in dict {
let val : NSObject = value as! NSObject;
if(val.isEqual(NSNull()))
{
dic.setValue("", forKey: (key as? String)!)
}
else
{
dic.setValue(value, forKey: key as! String)
}
}
return dic;
}
修剪Null表单NSDictionary以获取崩溃Pass Dictionary到此函数并获得结果为NSMutableDictionary
func trimNullFromDictionaryResponse(dic:NSDictionary) -> NSMutableDictionary {
let allKeys = dic.allKeys
let dicTrimNull = NSMutableDictionary()
for i in 0...allKeys.count - 1 {
let keyValue = dic[allKeys[i]]
if keyValue is NSNull {
dicTrimNull.setValue("", forKey: allKeys[i] as! String)
}
else {
dicTrimNull.setValue(keyValue, forKey: allKeys[i] as! String)
}
}
return dicTrimNull
}
尝试使用预期类型的值解包它并检查nill或如果是，则清空然后从字典中删除该值。
如果字典中的值具有空值，则此方法有效
使用compactMapValues：
dictionary.compactMapValues { $0 }
compactMapValues已在Swift 5中引入。有关更多信息，请参阅Swift提议SE-0218。
let json = [
"FirstName": "Anvar",
"LastName": "Azizov",
"Website": nil,
"About": nil,
]
let result = json.compactMapValues { $0 }
print(result) // ["FirstName": "Anvar", "LastName": "Azizov"]
let jsonText = """
{
"FirstName": "Anvar",
"LastName": "Azizov",
"Website": null,
"About": null
}
"""
let data = jsonText.data(using: .utf8)!
let json = try? JSONSerialization.jsonObject(with: data, options: [])
if let json = json as? [String: Any?] {
let result = json.compactMapValues { $0 }
print(result) // ["FirstName": "Anvar", "LastName": "Azizov"]
}
我会把filter和mapValues结合起来：
dictionary.filter { $0.value != nil }.mapValues { $0! }
使用上面的示例只需将let result替换为
let result = json.filter { $0.value != nil }.mapValues { $0! }
我在Swift 2中得到了这个结论：
extension Dictionary where Value: AnyObject {
var nullsRemoved: [Key: Value] {
let tup = filter { !($0.1 is NSNull) }
return tup.reduce([Key: Value]()) { (var r, e) in r[e.0] = e.1; return r }
}
}
对于Swift 3，答案相同：
extension Dictionary {
/// An immutable version of update. Returns a new dictionary containing self's values and the key/value passed in.
func updatedValue(_ value: Value, forKey key: Key) -> Dictionary<Key, Value> {
var result = self
result[key] = value
return result
}
var nullsRemoved: [Key: Value] {
let tup = filter { !($0.1 is NSNull) }
return tup.reduce([Key: Value]()) { $0.0.updatedValue($0.1.value, forKey: $0.1.key) }
}
}
在Swift 4中，事情变得容易多了。只需直接使用Dictionary的filter。
jsonResult.filter { !($0.1 is NSNull) }
或者，如果您不想删除相关密钥，则可以执行以下操作：
jsonResult.mapValues { $0 is NSNull ? nil : $0 }
这将用NSNull替换nil值而不是删除键。
假设您只想从字典中过滤掉任何NSNull值，这可能是更好的方法之一。就我现在所知，它可以防范Swift 3：
（感谢AirspeedVelocity的扩展，翻译为Swift 2）
import Foundation
extension Dictionary {
/// Constructs [key:value] from [(key, value)]
init<S: SequenceType
where S.Generator.Element == Element>
(_ seq: S) {
self.init()
self.merge(seq)
}
mutating func merge<S: SequenceType
where S.Generator.Element == Element>
(seq: S) {
var gen = seq.generate()
while let (k, v) = gen.next() {
self[k] = v
}
}
}
let jsonResult:[String: AnyObject] = [
"FirstName": "Anvar",
"LastName" : "Azizov",
"Website" : NSNull(),
"About" : NSNull()]
// using the extension to convert the array returned from flatmap into a dictionary
let clean:[String: AnyObject] = Dictionary(
jsonResult.flatMap(){
// convert NSNull to unset optional
// flatmap filters unset optionals
return ($0.1 is NSNull) ? .None : $0
})
// clean -> ["LastName": "Azizov", "FirstName": "Anvar"]
建议使用此方法，展平可选值并兼容Swift 3
String键，带有nil值的可选AnyObject?值字典：
let nullableValueDict: [String : AnyObject?] = [
"first": 1,
"second": "2",
"third": nil
]
// ["first": {Some 1}, "second": {Some "2"}, "third": nil]
删除nil值并转换为非可选值字典
nullableValueDict.reduce([String : AnyObject]()) { (dict, e) in
guard let value = e.1 else { return dict }
var dict = dict
dict[e.0] = value
return dict
}
// ["first": 1, "second": "2"]
由于删除了swift 3中的var参数，因此需要重新声明var dict = dict，因此对于swift 2,1，它可能是;
nullableValueDict.reduce([String : AnyObject]()) { (var dict, e) in
guard let value = e.1 else { return dict }
dict[e.0] = value
return dict
}
斯威夫特4，将是;
let nullableValueDict: [String : Any?] = [
"first": 1,
"second": "2",
"third": nil
]
let dictWithoutNilValues = nullableValueDict.reduce([String : Any]()) { (dict, e) in
guard let value = e.1 else { return dict }
var dict = dict
dict[e.0] = value
return dict
}
由于Swift 4为类reduce(into:_:)提供方法Dictionary，您可以使用以下函数从Dictionary中删除nil-values：
func removeNilValues<K,V>(dict:Dictionary<K,V?>) -> Dictionary<K,V> {
return dict.reduce(into: Dictionary<K,V>()) { (currentResult, currentKV) in
if let val = currentKV.value {
currentResult.updateValue(val, forKey: currentKV.key)
}
}
}
你可以这样测试：
let testingDict = removeNilValues(dict: ["1":nil, "2":"b", "3":nil, "4":nil, "5":"e"])
print("test result is \(testingDict)")
compactMapValues（_ :)
返回一个新字典，该字典仅包含具有非零值的键值对，作为给定闭包转换的结果。
let people = [
"Paul": 38,
"Sophie": 8,
"Charlotte": 5,
"William": nil
]
let knownAges = people.compactMapValues { $0 }
我只需要解决这个问题，一般情况下NSNulls可以嵌套在任何级别的字典中，甚至可以是数组的一部分：
extension Dictionary where Key == String, Value == Any {
func strippingNulls() -> Dictionary<String, Any> {
var temp = self
temp.stripNulls()
return temp
}
mutating func stripNulls() {
for (key, value) in self {
if value is NSNull {
removeValue(forKey: key)
}
if let values = value as? [Any] {
var filtered = values.filter {!($0 is NSNull) }
for (index, element) in filtered.enumerated() {
if var nestedDict = element as? [String: Any] {
nestedDict.stripNulls()
if nestedDict.values.count > 0 {
filtered[index] = nestedDict as Any
} else {
filtered.remove(at: index)
}
}
}
if filtered.count > 0 {
self[key] = filtered
} else {
removeValue(forKey: key)
}
}
if var nestedDict = value as? [String: Any] {
nestedDict.stripNulls()
if nestedDict.values.count > 0 {
self[key] = nestedDict as Any
} else {
self.removeValue(forKey: key)
}
}
}
}
}
我希望这对其他人有帮助，我欢迎改进！
（注意：这是Swift 4）
以下是解决方案，当JSON有sub-dictionaries。这将通过dictionaries的所有sub-dictionaries，JSON并从(NSNull)移除NULLkey-value JSON对。
extension Dictionary {
func removeNull() -> Dictionary {
let mainDict = NSMutableDictionary.init(dictionary: self)
for _dict in mainDict {
if _dict.value is NSNull {
mainDict.removeObject(forKey: _dict.key)
}
if _dict.value is NSDictionary {
let test1 = (_dict.value as! NSDictionary).filter({ $0.value is NSNull }).map({ $0 })
let mutableDict = NSMutableDictionary.init(dictionary: _dict.value as! NSDictionary)
for test in test1 {
mutableDict.removeObject(forKey: test.key)
}
mainDict.removeObject(forKey: _dict.key)
mainDict.setValue(mutableDict, forKey: _dict.key as? String ?? "")
}
if _dict.value is NSArray {
let mutableArray = NSMutableArray.init(object: _dict.value)
for (index,element) in mutableArray.enumerated() where element is NSDictionary {
let test1 = (element as! NSDictionary).filter({ $0.value is NSNull }).map({ $0 })
let mutableDict = NSMutableDictionary.init(dictionary: element as! NSDictionary)
for test in test1 {
mutableDict.removeObject(forKey: test.key)
}
mutableArray.replaceObject(at: index, with: mutableDict)
}
mainDict.removeObject(forKey: _dict.key)
mainDict.setValue(mutableArray, forKey: _dict.key as? String ?? "")
}
}
return mainDict as! Dictionary<Key, Value>
}
}