无法使用类型为((String?)'的参数列表调用类型为'Double'的初始化程序

问题描述

我有两个问题:

let amount:String? = amountTF.text

1. amount?.characters.count <= 0

出现错误:

Binary operator '<=' cannot be applied to operands of type 'String.CharacterView.IndexDistance?' (aka 'Optional<Int>') and 'In

1. let am = Double(amount)

出现错误:

Cannot invoke initializer for type 'Double' with an argument list of type '(String?)'

我不知道该怎么解决.

推荐答案

amount?.count <= 0，此处金额是可选的.您必须确保它不是nil.

amount?.count <= 0 here amount is optional. You have to make sure it not nil.

let amount:String? = amountTF.text
if let amountValue = amount, amountValue.count <= 0 {

}

amountValue.count <= 0仅在amount不为零时被调用.

amountValue.count <= 0 will only be called if amount is not nil.

与此let am = Double(amount)相同的问题. amount是可选的.

Same issue for this let am = Double(amount). amount is optional.

if let amountValue = amount, let am = Double(amountValue) {
       // am
}

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