如何在 swift 中的文本字段委托方法中将文本字段输入的金额与总金额进行比较

Question

我需要将输入的文本字段值与 totalValue 进行比较，然后需要以红色显示一条错误消息

为此，我尝试了以下代码：这里我的总金额是 180...如果我在文本字段中输入 181，我需要显示红色文本，但只有当我输入 4 个字符时才会显示，例如 1811 然后显示但我我在文本字段中输入 181 后需要立即...我错在哪里？ 请指导我。

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
print(string)
if textField == self.amountTextField {
    if let char = string.cString(using: String.Encoding.utf8) {
        let isBackSpace = strcmp(char, "\\b")
        let enteredAmount = textField.text
        let totalAmnt = 180

        if enteredAmount?.toInteger() ?? 0 >= totalAmnt.toInteger(){
            amntErrorLbl.text = "Payment being made is more than quote"
        }
    }
}
return true
} 

o/p 截图：

如果我在文本字段中输入 181 然后 o/p

如果我添加 4 个数字，那么 o/p

Answer 1

var totalAmount = 180

func textFieldDidChangeSelection(_ textField: UITextField) {
    guard let text = textField.text,text.isNumbers else {
        return
    }
    guard let enteredAmount = Int(text) else {
        return
    }
    if enteredAmount > totalAmount {
        amntErrorLbl.text = "Entered more than total amount"
    }
    if enteredAmount < totalAmount {
        amntErrorLbl.text = "Entered less than total amount"
    }
    if enteredAmount == totalAmount {
        amntErrorLbl.text = "Entered equal amount"
    }
    
}


extension String {
    var isNumbers:Bool {
        guard self.count > 0 else { return false }
        let nums: Set<Character> = ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"]
        return Set(self).isSubset(of: nums)
    }
}