如何使用 属性 观察者观察具有 Swift 集合类型的特定元素?
How can I observe a specific element with Swift collection types using property observers?
在回答的问题时受到启发,答案是使用属性观察者来检查数组是否已被修改。
但是,如何在 属性 观察者中确定 is/are 集合类型中更新的元素?例如:
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,每个添加、更新或删除操作都调用了 didSet
代码,但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
数组作为 属性 Observer?
我问的是 Swift 中的所有集合类型,因为我假设所有集合类型的行为都应该相同,这是关于观察的。
谢谢。
您可以在应用更改之前使用 willSet
观察器计算更改。像这样:
struct YourStruct {
var strings : [ String ] = [ "Hello", "World", "!" ] {
willSet {
// in here you have `newValue` containing the new array which
// will be set. Do any comparison operations you want, like:
let oldStrings = Set(strings)
let newStrings = Set(newValue)
print("removed: \(oldStrings.substract(newStrings))")
print("added: \(newStrings.substract(oldStrings))")
// (Just for demonstration purposes, if they are Sets, they
// should be Sets in the first place, obviously.)
}
}
}
感谢@hnh,基于他的 ,我得到了:
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): []
----------
*/
这里展示了如何处理数组、集合和字典。
在回答
但是,如何在 属性 观察者中确定 is/are 集合类型中更新的元素?例如:
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,每个添加、更新或删除操作都调用了 didSet
代码,但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
数组作为 属性 Observer?
我问的是 Swift 中的所有集合类型,因为我假设所有集合类型的行为都应该相同,这是关于观察的。
谢谢。
您可以在应用更改之前使用 willSet
观察器计算更改。像这样:
struct YourStruct {
var strings : [ String ] = [ "Hello", "World", "!" ] {
willSet {
// in here you have `newValue` containing the new array which
// will be set. Do any comparison operations you want, like:
let oldStrings = Set(strings)
let newStrings = Set(newValue)
print("removed: \(oldStrings.substract(newStrings))")
print("added: \(newStrings.substract(oldStrings))")
// (Just for demonstration purposes, if they are Sets, they
// should be Sets in the first place, obviously.)
}
}
}
感谢@hnh,基于他的
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): []
----------
*/
这里展示了如何处理数组、集合和字典。