我正在使用时间计算器来尝试学习Swift，而且我遇到了格式化用户输入导致访问错误的问题。
以下是导致崩溃的代码（最初包含在循环中但是为了找到问题而分解）：
var outputString : String = ""
let prefixString : String = "00"
let combinedString1 : String = prefixString + self.timeIntervalInput[0]
let combinedString1a : String = combinedString1.substringFromIndex(countElements(combinedString1) - 2)
outputString += combinedString1a
let combinedString2 : String = prefixString + self.timeIntervalInput[1]
let combinedString2a : String = combinedString2.substringFromIndex(countElements(combinedString2) - 2)
outputString += combinedString2a // CRASH USUALLY HAPPENS HERE
let combinedString3 : String = prefixString + self.timeIntervalInput[2]
let combinedString3a : String = combinedString3.substringFromIndex(countElements(combinedString3) - 2)
outputString += combinedString3a
用户的输入存储在字符串数组中（小时/分钟/秒/毫秒）。上面的代码应该用0填充间隙（因此2变为02，空字符串变为00等），并且每次更新用户的输入时都会运行。
输入第一个或第二个字符后，上面的代码崩溃了。将prefixString从let更改为var会使其在稍长时间内正常工作，因此它会在第三个字符后崩溃。
我在这里做错了什么，或者这是Swift中的错误？
修改（附加信息）：
这是整个结构：
struct TimeCalcInput
{
var timeIntervalInput : String[] = ["", "", "", ""]
var timeIntervalIndex : Int = 0
var decimalInput : String = ""
var timeType : TimeTypeEnum = TimeTypeEnum.AM
var potentialInput : String = ""
var label : String {
get {
if (self.timeType == TimeTypeEnum.Decimal) {
return self.decimalInput
} else {
// var outputString : String = ""
// for (var i : Int = 0; i < 3; i++) {
// let prefixString : String = "00"
// var combinedString : String = ""
// combinedString += prefixString + self.timeIntervalInput[i]
// combinedString = combinedString.substringFromIndex(countElements(combinedString) - 2)
// outputString = outputString + "\(combinedString)"
// }
var outputString : String = ""
let prefixString : String = "00"
let combinedString1 : String = prefixString + self.timeIntervalInput[0]
let combinedString1a : String = combinedString1.substringFromIndex(countElements(combinedString1) - 2)
outputString += combinedString1a
let combinedString2 : String = prefixString + self.timeIntervalInput[1]
let combinedString2a : String = combinedString2.substringFromIndex(countElements(combinedString2) - 2)
outputString += combinedString2a // CRASH USUALLY HAPPENS HERE
let combinedString3 : String = prefixString + self.timeIntervalInput[2]
let combinedString3a : String = combinedString3.substringFromIndex(countElements(combinedString3) - 2)
outputString += combinedString3a
return ""
let test : String = "000"
var asd : String = test + self.timeIntervalInput[3]
asd = asd.substringFromIndex(countElements(asd) - 3)
outputString += asd
if (self.timeType == TimeTypeEnum.AM) {
outputString += " AM"
} else if (self.timeType == TimeTypeEnum.PM) {
outputString += " PM"
}
println(outputString)
return outputString
}
}
}
mutating func validateNewInput(inputString : String) -> Bool
{
switch (self.timeType)
{
case TimeTypeEnum.Decimal:
return self.validateNewInputForDecimal(inputString)
case TimeTypeEnum.Interval:
// return self.validateNewInputForInterval(inputString)
return false
case TimeTypeEnum.AM, TimeTypeEnum.PM:
var temp : Bool = self.validateNewInputForRawTime(inputString, isMilitaryTime:false)
println(self.timeIntervalInput)
return temp
case TimeTypeEnum.Military:
var temp : Bool = self.validateNewInputForRawTime(inputString, isMilitaryTime:true)
println(self.timeIntervalInput)
return temp
default:
return false
}
}
mutating func validateNewInputForDecimal(inputString : String) -> Bool
{
let combinedString : String = self.decimalInput + inputString
// note: this regex fails on letters-only strings. not an issue now but something to watch
let predicate : NSPredicate = NSPredicate(format: "SELF MATCHES '^[0-9]*(\\.[0-9]*)'")
let stringTest : Bool = predicate.evaluateWithObject(combinedString)
if (stringTest) {
self.decimalInput = combinedString
return true
}
return false
}
// used to evaluate an incoming string when the string is assumed to represent a raw time (e.g. 5:30am)
// since the string is being built one character at a time, each character needs to be evaluated separately
// to ensure that the final time is valid
mutating func validateNewInputForRawTime(inputString : String, isMilitaryTime : Bool) -> Bool
{
let currentString = self.timeIntervalInput[self.timeIntervalIndex]
// if the incoming value is a ":" assume the user wants to move on to the next section
// (e.g. hours --> minutes). Fill in any gaps in the current section, then advance to the next section
if (inputString == ":") {
// check to make sure there is a "next" section
if (self.timeIntervalIndex < self.timeIntervalInput.count - 1)
{
// if the current section is incomplete, fill any gaps with 0s
let prefixString = "00"
var combinedString = prefixString + currentString
combinedString = combinedString.substringFromIndex(countElements(combinedString) - 2)
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
// go to the next section
self.timeIntervalIndex++
return true
}
// if the incoming value is a number, evaluate it to make sure it's valid, and if so, add it
} else {
let combinedString = currentString + inputString
// each section (hours, minutes, etc, has its own rules for whether the input is valid
switch (self.timeIntervalIndex)
{
// hours
case 0:
// if empty, accept any number
if (countElements(currentString) == 0) {
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
return true
// if one digit exists, make sure total value is less than 12/24 (format depending)
} else if (countElements(currentString) == 1) {
if ((combinedString.toInt() < 24 && isMilitaryTime) || (combinedString.toInt() < 12)) {
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
return true
}
// if both digits exist, skip to the next section and add it
} else {
self.timeIntervalIndex++
self.timeIntervalInput[self.timeIntervalIndex] = inputString
return true
}
// minutes, seconds
case 1, 2:
// if empty, accept any number
if (countElements(currentString) == 0) {
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
return true
// if one digit exists, make sure total value is less than 60
} else if (countElements(currentString) == 1) {
if (combinedString.toInt() < 60) {
let combinedString = currentString + inputString
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
return true
}
// if both digits exist, skip to the next section and add it
} else {
self.timeIntervalIndex++
self.timeIntervalInput[self.timeIntervalIndex] = inputString
return true
}
// milliseconds
case 3:
// accept any combined total less than 1000
if (combinedString.toInt() < 1000) {
let combinedString = currentString + inputString
self.timeIntervalInput[self.timeIntervalIndex] = combinedString
return true
}
default:
break
}
}
return false
}
}
在这里使用它（输入是上述结构的数组）：
// -----------------------------------------------------------------------------------------------------------------
@IBAction func addInputCharacter(#sender : UIButton)
{
let inputChar : String = String(sender.tag)
self.inputs[self.currentInput].validateNewInput(inputChar)
self.updateLabelsAfterInput()
}
// -----------------------------------------------------------------------------------------------------------------
func updateLabelsAfterInput()
{
self.lblMainLabel.text = self.inputs[self.currentInput].label
if (self.currentInput == 0) {
self.lblSecondaryLabel.text = ""
} else {
self.lblSecondaryLabel.text = self.inputs[0].label
}
}
用户首次输入号码时会发生崩溃。我在没有更新标签的情况下测试了它，并且timeIntervalInputs数组完全设置好了（输入＆＃34; 1＆＃34;后，数组读取[1 ,,,]，然后输入0变为[10， ,,]，）
崩溃时的错误消息是
在崩溃之前，线程1：EXC_BAD_ACCESS（代码= 1，地址= 0x12aff2cf0）
combinedString2a正在存储正确的值（＆＃34; 00＆＃34;）。崩溃后，Quick Look表示值为＆＃34;（无）＆＃34;并打印描述给出以下消息：
（String）combinedString2a = DW_OP_piece for offset 8：stack of top is 不是一块
答案 0 :(得分：1)
我一直在遇到同样的错误，我只能认为它是Swift中的一个错误。这是一个非常简单的例子。 txtName是文本字段的IBOutlet，用户在其中键入其名称，labResult是放置结果的标签。在下面的代码中，一旦我们尝试调用.lowercaseString方法，我们每次都会在modifyString中遇到错误。 （我对Swift和iOS编程都很新，所以我可能会犯一些愚蠢的错误，但我不知道是什么。）
@IBAction func butDoIt_Clicked(sender : UIButton) {
var myName = "Fred Bloggs"
labResult.text = modifyString(myName) //this works just fine
if txtName.text
{
myName = txtName.text!
labResult.text = modifyString(myName) //this crashes with EXC-BAD-ACCESS
}
}
func modifyString(aName:String) ->String
{
let lowername = aName.lowercaseString
let uppername = aName.uppercaseString
return lowername + "-" + uppername
}
答案 1 :(得分：1)
我已经向Apple提交了一份错误报告。与此同时，我通过用NSStrings替换组合字符串并使用方法的NSString版本找到了一种解决方法。
var outputString : String = ""
let prefixString : String = "00"
let combinedString1 : NSString = prefixString.stringByAppendingString(self.timeIntervalInput[0])
let combinedString1a : NSString = combinedString1.substringFromIndex(combinedString1.length - 2)
outputString += combinedString1a
let combinedString2 : NSString = prefixString.stringByAppendingString(self.timeIntervalInput[1])
let combinedString2a : NSString = combinedString2.substringFromIndex(combinedString2.length - 2)
outputString += combinedString2a
let combinedString3 : NSString = prefixString.stringByAppendingString(self.timeIntervalInput[2])
let combinedString3a : NSString = combinedString3.substringFromIndex(combinedString3.length - 2)
outputString += combinedString3a
return outputString