二进制运算符'<'不能应用于两个'Int?'操作数 [英] Binary operator '<' cannot be applied to two 'Int?' operands

问题描述

晚上好可爱的社区，
这是我的第一篇文章，如果我做错了，请留意.
我知道这里也有类似的问题，但我不明白.
也许我理解，如果有人在我的代码中解释它.

Good evening lovely community,
this is my first post, please have mercy, if I do something wrong.
I know there are some similar questions here, but I doesn't understand it.
Maybe I understand, if someone explain it on my code.

//这是我的两个TextField和完成"按钮.

// these are my two TextFields and the "finish"-Button.

@IBOutlet weak var goalPlayerOne: UITextField!
@IBOutlet weak var goalPlayerTwo: UITextField!
@IBOutlet weak var finishedGameButton: UIButton!

//这是我的功能，它应该告诉我，哪个玩家赢得了A< B，所以B赢了.

// here are my function, it should tell me, which Player has won like A < B, so B has won.

 @IBAction func finishedGameButtonPressed(_ sender: Any) {
    // define UITextField as Integer

let goalPlayerOne = "";
let goalOne = Int(goalPlayerOne);

let goalPlayerTwo = "";
let goalTwo = Int(goalPlayerTwo);

//这是问题所在:
二进制运算符'<'不能应用于两个'Int?'操作数"
//如果我制作了'=='，那么就可以了

// here is the problem:
"Binary operator '<' cannot be applied to two 'Int?' operands"
// if I make a '==' it works

if goalOne < goalTwo{    
    displayMyAlertMessage(userMessage: "Player Two wins")
    return
}

推荐答案

如果查看采用String的Int初始化程序的声明，您可以在init之后通过?看到它返回一个可选的:

If you look at the declaration for Int's initializer that takes a String, you can see by the ? after init that it returns an optional:

convenience init?(_ description: String)

这意味着您必须先拆开包装，然后才能执行大多数操作(==是一个例外，因为Optional类型对该操作符有重载).

This means you have to unwrap it before you can do most things with it (== is an exception, since the Optional type has an overload for that operator).

有四种主要方法可以解开可选项:

There are four main ways to unwrap your optionals:

if let goalOne = Int(someString) {
    // do something with goalOne
}

2:后卫放手

guard let goalOne = Int(someString) else {
    // either return or throw an error
}

// do something with goalOne

3:map和/或flatMap

3: map and/or flatMap

let someValue = Int(someString).map { goalOne in
    // do something with goalOne and return a value
}

4:提供默认值

let goalOne = Int(someString) ?? 0 // Or whatever the default value should be

如果解开所有可选选项，则可以按预期进行比较.

If you unwrap all your optionals, you'll be able to compare them as you expect.

这篇关于二进制运算符'&lt;'不能应用于两个'Int?'操作数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！