decodeDouble
上的NSCoder
返回一个非可选值,但我想确定在编码之前该值是否为nil。
这是我的情况:
var optionalDouble: Double? = nil
func encode(with aCoder: NSCoder) {
if let optionalDouble {
aCoder.encode(optionalDouble, forKey: "myOptionalDouble")
}
}
convenience required init?(coder aDecoder: NSCoder) {
optionalDouble = aDecoder.decodeDouble(forKey: "myOptionalDouble")
// here optionalDouble is never nil anymore
}
因此,如果从未设置过该值,则对double进行解码会返回
0
,因此似乎我无法在编码之前确定该值是0
还是nil
有没有办法让我检查双精度在编码之前是否为零?
最佳答案
解决方案是在编码时使用NSNumber而不是Double,然后使用encodeObject返回(如果存在)双精度值。例如
class A: NSCoding {
var optionalDouble: Double? = nil
@objc func encodeWithCoder(aCoder: NSCoder) {
if let optionalDouble = optionalDouble {
aCoder.encodeObject(NSNumber(double: optionalDouble), forKey: "myOptionalDouble")
}
}
@objc required init?(coder aDecoder: NSCoder) {
if let decodedDoubleNumber = aDecoder.decodeObjectForKey("myOptionalDouble") as? NSNumber {
self.optionalDouble = decodedDoubleNumber.doubleValue
} else {
self.optionalDouble = nil
}
}
}
在@Hamish的建议下,这是Swift 3的版本。请注意,我们需要将类继承到NSObject才能使NSEncoding工作(Got Unrecognized selector -replacementObjectForKeyedArchiver: crash when implementing NSCoding in Swift)
class A: NSObject, NSCoding {
var optionalDouble: Double? = nil
func encode(with aCoder: NSCoder) {
if let optionalDouble = optionalDouble {
aCoder.encode(optionalDouble, forKey: "myOptionalDouble")
}
}
override init() {
super.init()
}
required init?(coder aDecoder: NSCoder) {
optionalDouble = aDecoder.decodeObject(forKey: "myOptionalDouble") as? Double
}
}
关于ios - NSCoder encodeDouble可选值,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/40785028/