可选类型 CGFloat 的值未在 Swift 中解开错误 [英] Value of optional type CGFloat not unwrapped error in Swift

问题描述

代码:

var loadView = UIView(frame: CGRectMake(0, 0, self.window?.frame.size.width, self.window?.frame.size.height))

我尝试以编程方式创建一个 UIView.当尝试为视图设置窗口高度和宽度时，它给出的错误是可选类型 'CGFloat 的值?'未解开；您是想使用！"吗?或者 '?'?"为什么显示此错误?任何帮助将不胜感激.提前致谢

I try to create a UIView progrmatically.when try to set window height and width for view it gives error as "Value of optional type 'CGFloat?' not unwrapped; did you mean to use '!' or '?'?" why this error showing?any help will be appreciated.thanks in advance

推荐答案

您正在使用 可选链，这意味着 self.window?.frame.width 计算为有效整数，如果 window 不是 nil，否则计算结果为 nil - height 相同.

You are using optional chaining, which means that self.window?.frame.width evaluates to a valid integer if window is not nil, otherwise it evaluates to nil - same for height.

因为你不能创建一个包含 nil 的 CGRect(或者更好的说法，CGRectMake 不接受它的任何参数的可选项)，编译器将其报告为错误.

Since you cannot make a CGRect containing nil (or better said, CGRectMake doesn't accept an optional for any of its arguments), the compiler reports that as an error.

解决方案是隐式解包self.window:

    var loadView = UIView(frame: CGRectMake(0, 0, self.window!.frame.size.width, self.window!.frame.size.height))

但是，如果 self.window 是 nil，则会引发运行时错误.用可选绑定包围它总是更好的做法:

But that raises a runtime error in the event that self.window is nil. It's always a better practice to surround that with a optional binding:

if let window = self.window {
    var loadView = UIView(frame: CGRectMake(0, 0, window.frame.size.width, window.frame.size.height))
    .... do something with loadVIew
}

这样你就可以确定只有在 self.window 实际上不是 nil 时才会创建视图.

so that you are sure the view is created only if self.window is actually not nil.

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