Swift：创建一个UIImage数组 [英] Swift: Creating an array of UIImage

问题描述

使用Swift，我正在尝试为简单动画创建一个UIImage对象数组。 animationImages 的上下文帮助读取数组必须包含UI图像对象。

Using Swift, I'm trying to create an array of UIImage objects for a simple animation. Contextual help for animationImages reads, "The array must contain UI Image objects."

我试图创建所述数组如下所示，但似乎无法使语法正确：

I've tried to create said array as follows, but can't seem to get the syntax correct:

var logoImages: UIImage[]
logoImages[0] = UIImage(name: "logo.png")

此抛出：
！在初始化之前使用的变量logoImages

This throws: ! Variable logoImages used before being initialized

然后我尝试了

var logoImages = []
logoImages[0] = UIImage(named: "logo.png")

哪个投掷：
！无法分配到此表达式的结果

Which throws: ! Cannot assign to the result of this expression

我在这里检查了文档，但上下文不一样：
https://developer.apple.com/library/content/documentation/Swift/Conceptual /Swift_Programming_Language/CollectionTypes.html

I've checked the docs here, but the context isn't the same: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/CollectionTypes.html

推荐答案

你有两个问题（没有正则表达式！）

You have two problems (and without a regex!)

var logoImages: [UIImage] = []

或

var logoImages: Array<UIImage> = []

或

var logoImages = [UIImage]()

或

var logoImages = Array<UIImage>()

2。如果要将新对象添加到数组中，则应使用 Array.append（）或一些等效的语法糖：

2. If you want to add new objects to an array, you should use Array.append() or some of the equivalent syntactic sugar:

logoImages.append(UIImage(named: "logo.png")!)

或

logoImages += [UIImage(named: "logo.png")!]

或

logoImages += [UIImage(named: "logo.png")!, UIImage(named: "logo2.png")!]

您需要附加到数组，因为（摘录来自文档）：

You need to append to the array because (excerpt from docs):

你不能使用下标语法将新项追加到
数组的末尾。如果您尝试使用下标语法为数组现有边界之外的索引检索或设置值
，则
将触发运行时错误。但是，通过将索引与数组的count属性进行比较，可以在使用之前检查索引是否有效
。当count为0（意味着数组为空）时，
除外，数组中最大的有效索引
将始终为count-1，因为数组的索引是
零。

You can’t use subscript syntax to append a new item to the end of an array. If you try to use subscript syntax to retrieve or set a value for an index that is outside of an array’s existing bounds, you will trigger a runtime error. However, you can check that an index is valid before using it, by comparing it to the array’s count property. Except when count is 0 (meaning the array is empty), the largest valid index in an array will always be count - 1, because arrays are indexed from zero.

当然，你可以随时简化它：

Of course you could always simplify it when possible:

var logoImage: [UIImage] = [
    UIImage(named: "logo1.png")!,
    UIImage(named: "logo2.png")!
]

编辑请注意，UIImage现在有一个< a href =https://developer.apple.com/swift/blog/?id=17>failable初始化程序，这意味着它返回一个可选项。我已更新所有代码位以反映此更改以及对数组语法的更改。

edit: Note that UIImage now has a "failable" initializer, meaning that it returns an optional. I've updated all the bits of code to reflect this change as well as changes to the array syntax.

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