Ios 检查可选数组是否为空

在Objective-C中，当我有一个数组时

NSArray *array;

我想检查它是否为空，我总是这样做：

if (array.count > 0) {
    NSLog(@"There are objects!");
} else {
    NSLog(@"There are no objects...");
}

这样，就不需要检查

array==nil

，因为这种情况会导致代码落入

else

的情况，以及非

nil

的情况，但空数组也可以

然而，在Swift中，我偶然发现我有一个可选数组：

var array: [Int]?

我无法确定使用哪种条件。我有一些选择，比如：

选项A:在相同条件下检查非

nil

和空案例：

if array != nil && array!.count > 0 {
    println("There are objects")
} else {
    println("No objects")
}

选项B:使用

let

解除阵列绑定：

if let unbindArray = array {
    if (unbindArray.count > 0) {
        println("There are objects!")
    } else {
        println("There are no objects...")
    }
} else {
    println("There are no objects...")
}

选项C:使用Swift提供的合并运算符：

if (array?.count ?? 0) > 0 {
    println("There are objects")
} else {
    println("No objects")
}

我不太喜欢选项B，因为我在两种情况下重复代码。但是我不确定选项A和C是否正确，或者我应该使用其他方法

我知道根据情况可以避免使用可选数组，但在某些情况下，可能需要询问它是否为空。所以我想知道最简单的方法是什么

---

编辑：

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

正如@vacawama指出的，这种简单的检查方法是有效的：

if array?.count > 0 {
    println("There are objects")
} else {
    println("No objects")
}

但是，我尝试了这样一种情况：我只想在

nil

或空时执行一些特殊操作，然后继续执行，而不管数组是否包含元素。所以我试着：

if array?.count == 0 {
    println("There are no objects")
}

// Do something regardless whether the array has elements or not.

而且

if array?.isEmpty == true {
    println("There are no objects")
}

// Do something regardless whether the array has elements or not.

但是，当数组为

nil

时，它不属于

if

主体。这是因为，在这种情况下，

array？.count==nil

和

array？.isEmpty==nil

，因此表达式

array？.count==0

和

array？.isEmpty==true

的计算结果都是

false

因此，我试图找出是否有任何方法可以通过一个条件实现这一点。

更新了Swift 3及以上版本的答案： Swift 3已经取消了将选项与

和

（lhs:T？、rhs:T？->Bool

进行比较的功能，这意味着编译器将

0

包装为

Int？

，这样，由于可选的链接调用，可以与左侧的

Int？

进行比较

以类似的方式，您可以执行以下操作：

if array?.isEmpty == false {
    print("There are objects")
} else {
    print("No objects")
}

注意：您必须在此处显式地与

false

进行比较，才能使其起作用

---

如果要在数组为

nil

或为空时执行某些操作，则至少有7种选择：

选项A:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项B:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项C:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项D:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项E:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项F:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

选项G:

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

---

选项D准确地捕捉了您用英语描述它的方式：只有当它为零或为空时，我才想做一些特别的事情。我建议您使用它，因为它很容易理解。这并没有什么问题，特别是当变量为

nil

条件展开时，它会“短路”并跳过空检查：

if let anArray = array {
    if !anArray.isEmpty {
        //do something
    }
}

编辑：可能从Swift 1.2开始：

if let myArray = array where !myArray.isEmpty {
    // do something with non empty 'myArray'
}

编辑：可能自Swift 2.0起：

guard let myArray = array where !myArray.isEmpty else {
    return
}
// do something with non empty 'myArray'

---

选项D:如果数组不需要是可选的，因为您只关心它是否为空，请将其初始化为空数组，而不是可选数组：

var array = [Int]()

现在它将一直存在，您只需检查

isEmpty

集合

协议上的扩展属性 *用Swift 3书写

extension Optional where Wrapped: Collection {
    var isNilOrEmpty: Bool {
        switch self {
            case .some(let collection):
                return collection.isEmpty
            case .none:
                return true
        }
    }
}

示例用法：

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if !(array?.count > 0) {
    print("There are no objects")
}

if !(array?.isEmpty == false) {
    print("There are no objects")
}

if array == nil || array!.count == 0 {
    print("There are no objects")
}

if array == nil || array!.isEmpty {
    print("There are no objects")
}

if (array ?? []).isEmpty {
    print("There are no objects")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

if (array?.count ?? 0) == 0 {
    print("There are no objects")
}

if array.isNilOrEmpty {
    print("The array is nil or empty")
}

其他选择 除了上面的扩展，我发现以下选项在没有强制展开选项的情况下最清晰。我将此理解为展开可选数组，如果为nil，则替换相同类型的空数组。然后，获取（非可选）结果，如果

为空，则执行条件代码

推荐

if (array ?? []).isEmpty {
    print("The array is nil or empty")
}

虽然下面的内容读得很清楚，但我建议尽量避免强制展开选项。虽然您可以保证
array
在
array！时永远不会
nil
！。如果在这种特定情况下执行isEmpty
，则以后很容易对其进行编辑，并在无意中导致崩溃。当您习惯使用强制展开选项时，您增加了将来有人进行更改的可能性，该更改会编译但在运行时崩溃

不推荐

if array == nil || array!.isEmpty {
    print("The array is nil or empty")
}

我发现包含
数组？
（可选链接）的选项令人困惑，例如：

令人困惑？

if !(array?.isEmpty == false) {
    print("The array is nil or empty")
}

if array?.isEmpty ?? true {
    print("There are no objects")
}

Swift 3-4兼容：

extension Optional where Wrapped: Collection {
        var nilIfEmpty: Optional {
            switch self {
            case .some(let collection):
                return collection.isEmpty ? nil : collection
            default:
                return nil
            }
        }

        var isNilOrEmpty: Bool {
            switch self {
            case .some(let collection):
                return collection.isEmpty
            case .none:
                return true
        }
}

用法：

guard let array = myObject?.array.nilIfEmpty else { return }

或

优雅的内置解决方案是可选的
map
方法。这种方法经常被遗忘，但它正是您在这里所需要的；它允许你发送一条信息给包裹在一个可选的、安全的文件中的东西。在这种情况下，我们使用了一种三向开关：我们可以对可选数组说
isEmpty
，然后得到true、false或nil（如果数组本身为nil）

与其使用
if
和
else
检查空数组，不如使用
guard
检查空数组，而不为同一数组创建新变量

guard !array.isEmpty else {
    return
}
// do something with non empty ‘array’

最好使用if检查空数组。为什么是bcoz，例如，如果我们试图在列表数组中查找最大整数，显然我们会将列表[0]与列表中的每个整数进行比较。当时它给了我们索引超出范围的异常。。。。您可以同时使用IF和Guard进行尝试

func findGreatestInList(list: [Int]?)-> Int? {
        if list!.count == 0 {
            print("List is empty")
            return nil
           
       }
       /*guard list!.isEmpty else {
            print("List is empty")
            return nil
        }*/
        var greatestValue = list![0]
            for number in 0...list!.count-1 {
            
              if list![number] > greatestValue {
                greatestValue = list![number]

他还要检查它是否是空的。这只是检查可选的是否包含数组。是的，然后您可以执行
if array？！=零&！（array！.isEmpty）{}
您可以简单地将其展开，因为如果arr