如何使用属性观察器观察Swift集合类型的特定元素? [英] How can I observe a specific element with Swift collection types using property observers?
问题描述
Inspired when answering the question of How do I know if a value of an element inside an array was changed?, The answer was using a Property Observer for checking if an array has been modified.
但是,如何确定属性查看器中集合类型中的已更新元素是什么?例如:
However, How can I determine what is/are the updated element(s) in a collection type in a property observer? For example:
class MyClass {
var strings: [String] = ["hello", "world", "!"] {
didSet(modifiedStrings) {
print("strings array has been modified!!:")
print(modifiedStrings)
}
}
}
let myClass = MyClass()
myClass.strings.append("a string")
myClass.strings[0] = "Hello"
myClass.strings.removeLast()
请注意,添加,更新或删除操作中的每一个都调用了didSet
代码,但是我如何才能确切知道受影响的元素是什么?有没有办法通过将strings
数组除以 Property Observer 来实现这一目标?
Note that the didSet
code has been called for each of adding, updating or deletion operation, but how can I exactly know what are the effected elements? is there even a way to achive this by decalring strings
array as a Property Observer?
我正在询问Swift中的所有集合类型,因为我认为对于所有它们而言,它应该是相同的行为,这与观察有关.
I am asking about all collection types in Swift because I assume that it should be the same behavior for all of them, it is about the observing.
谢谢.
推荐答案
感谢@hnh,基于他的 answer ,最后我得到了
Thanks for @hnh, based on his answer, I ended up with:
class MyNumber: NSObject {
// NOTE that it works in both "willSet" and "didSet"
/// Array ///
var arrayNumbers: [String] = ["one", "two", "three"] {
willSet {
let oldStrings = Set(arrayNumbers)
let newStrings = Set(newValue)
print("removed from array: \(oldStrings.subtracting(newStrings))")
print("added to array: \(newStrings.subtracting(oldStrings))")
print("----------")
}
}
/// Set ///
var setNumbers: Set = ["one", "two", "three"] {
didSet(newSet) {
print("removed from set: \(newSet.subtracting(setNumbers))")
print("added to set: \(setNumbers.subtracting(newSet))")
print("----------")
}
}
var dictionaryNumbers = ["1": "one", "2": "two", "3": "three"] {
didSet(modified) {
let oldKeys = Set(dictionaryNumbers.keys)
let newKeys = Set(modified.keys)
let oldValues = Set(dictionaryNumbers.values)
let newValues = Set(modified.values)
print("removed from dictionary (keys): \(newKeys.subtracting(oldKeys)) (values): \(newValues.subtracting(oldValues))")
print("added to dictionary (keys): \(oldKeys.subtracting(newKeys)) (values): \(oldValues.subtracting(newValues))")
print("----------")
// print("removed (values): \(newValues.subtracting(oldValues))")
// print("added (values): \(oldValues.subtracting(newValues))")
}
}
}
执行:
let myNumber = MyNumber()
/// Array ///
// adding:
myNumber.arrayNumbers.append("four")
/* Logging:
removed: [] means that nothing has been removed form the array
added: ["four"]
----------
*/
// updating:
myNumber.arrayNumbers[0] = "One"
/* Logging:
removed: ["one"]
added: ["One"]
----------
*/
// deleting:
myNumber.arrayNumbers.removeLast()
/* Logging:
removed: ["four"]
added: [] means that nothing has been added to the array
----------
*/
/// Set ///
// adding:
myNumber.setNumbers.insert("four")
/* Logging:
removed from set: [] means that nothing has been removed form the set
added to set: ["four"]
----------
*/
// deleting:
myNumber.setNumbers.removeFirst()
/* Logging:
removed from set: ["three"] // sets are unsorted...
added to set: [] means that nothing has been added to the set
----------
*/
/// Dictionary ///
// adding:
myNumber.dictionaryNumbers["4"] = "four"
/* Logging:
removed from dictionary (keys): [] (values): []
added to dictionary (keys): ["4"] (values): ["four"]
----------
*/
// updating:
myNumber.dictionaryNumbers["1"] = "One"
/* Logging:
removed from dictionary (keys): [] (values): ["one"]
added to dictionary (keys): [] (values): ["One"]
----------
*/
// deleting:
myNumber.dictionaryNumbers.removeValue(forKey: "2")
/* Logging:
removed from dictionary (keys): ["2"] (values): ["two"]
added to dictionary (keys): [] (values): []
----------
*/
这显示了如何处理数组,集合和字典.
This shows how to deal with array, set and dictionary.
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