swift - M 收到 fatal error : cannot decrement before startIndex. 请解决

Question

当我尝试执行以下代码时出现 fatal error :

 let truncated = "{" + stringToSend.substring(to: stringToSend.characters.index(before: stringToSend.endIndex)) + "}"
                //stringToSend = "tttttttttttttttttttttttttttttttttttttttttt" + truncated + "@"

Answer 1

您的错误发生是因为您的字符串为空或只有一个字符。

一个简单的 if 就可以解决这个问题。

swift 3

if stringToSend.count > 1{
   let truncated = stringToSend.substring(to: stringToSend.characters.index(before: stringToSend.endIndex))
}

swift 4:

if stringToSend.count > 1{
   let truncated = String(stringToSend[stringToSend.startIndex...stringToSend.index(before: stringToSend.endIndex)])
}