ios - 无法使用类型为 'Double' 的参数列表调用类型为 '(String?)' 的初始值设定项

Question

我有两个问题:

let amount:String? = amountTF.text

1. amount?.characters.count <= 0

报错:

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

1. let am = Double(amount)

报错:

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

我不知道怎么解决。

Answer 1

amount?.count <= 0这里的金额是可选的。你必须确保它不是nil .

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

}

amountValue.count <= 0只有在 amount 时才会被调用不为零。

同样的问题 let am = Double(amount) . amount是可选的。

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