Question

正如标题所说，Array vs NSArray与[AnyObject]之间有什么区别？

此外，最推荐的方法是什么。我的意思是推荐，最简单的实现是什么。谢谢。

Answer 1

Array是结构，因此它在Swift中是值类型。 NSArray是一个不可变的Objective C 类，因此它在Swift中是一个引用类型，它被桥接到Array<AnyObject>。 NSMutableArray是NSArray的可变子类。

var arr : NSMutableArray = ["Pencil", "Eraser", "Notebook"]
var barr = ["Pencil", "Eraser", "Notebook"]

func foo (var a : Array<String>)
{
    a[2] = "Pen"
}

func bar (a : NSMutableArray)
{
    a[2] = "Pen"
}

foo(barr)
bar(arr)

println (arr)
println (barr)

打印：

(
    Pencil,
    Eraser,
    Pen
)
[Pencil, Eraser, Notebook]

由于foo更改了a的本地值，bar更改了引用。如果您与其他参考类型一样let arr而不是var，它也会有效。

Answer 2

Array是一个Swift构造和泛型结构，这意味着它可以是任何特定类型的数组（Int，String，AnyObject等）

[T]是Array<T>

的语法糖

AnyObject是任何类的对象，包括Objective-C类。

NSArray是一个Objective-C构造，可以容纳任何Objective-C对象，并透明地映射到Array<AnyObject>

Answer 3

使用Krzak答案，这是一个实际的例子：

// Let´s create an Array as a struct showing alternative ways
    var arrStruct = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct: [String] = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct: Array = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct = Array(["Pencil", "Eraser", "Notebook"])
    // All this alternative ways create an array as struct

    // Now let´s create a function that modifies this array struct
    func modifyArr(alternativeArr: [String]) 
    // or func modify(alternativeArr: Array<String>)
    {
        alternativeArr[2] = "Pen" // compilation error
        // This won´t work. In swift >= 3.0 all func parametes are a let variable, 
        // this means alternativeArr is defined as a let. What one has to do is 
        // create a local variable and copy the value.

        var localAlternativeArr = alternativeArr
        // or var localAlternativeArr: [String] = alternativeArr
        // or var localAlternativeArr: Array = alternativeArr

        // now we can change it.
        localAlternativeArr[2] = "Pen"
        print(localAlternativeArr) // ["Pencil", "Eraser", "Pen"]
        print(alternativeArr) // ["Pencil", "Eraser", "Notebook"]
    }

    modifyArr(alternativeArr: arrStruct)
    print(arrStruct) // ["Pencil", "Eraser", "Notebook"]

    // Since the arrStruct is a struct every time we assign to another variable or 
    // pass it as a func argument a copy is made.



// Now let´s create as an NSMutableArray
    var arrClass: NSMutableArray = ["Pencil", "Eraser", "Notebook"]
    // or var arrStruct = NSMutableArray(array: ["Pencil", "Eraser", "Notebook"])
    // All this create an NSMutableArray as a class

    // Now let´s create a function that modifies this array struct
    func modifyArr(alternativeArr: NSMutableArray)
    {
        alternativeArr[2] = "Pen"
        print(alternativeArr)
        // (
        //   Pencil,
        //   Eraser,
        //   Pen
        // )
    }

    modifyArr(alternativeArr: arrClass)
    print(arrClass)
    // (
    //   Pencil,
    //   Eraser,
    //   Pen
    // )

    // Since the arrClass is a class everytime we assign to another variable or 
    // pass it as a func argument is passed by reference. Means that any change
    // inside modifyArr is going to change the arrClass outside. The change 
    // is made in the same pointer.

Answer 4

除了@Krzak的出色答案之外，这就是原因

print(NSArray().object(at: 1))   // Triggers an UnmanagedException

2018-11-09 11：38：08.798088-0600 AppName [38786：10497909] *由于未捕获的异常'NSRangeException'而终止应用程序，原因：'* -[__ NSArray0 objectAtIndex：]：空NSArray的范围超出索引1”

和

print(Array<Int>()[1])  // Halts with "Thread 1: Fatal error: Index out of range"

对错误的这种不同处理有助于我理解差异..... e

在Swift中：数组VS NSArray VS [AnyObject]之间的差异

4 个答案: