斯威夫特4.2

我还删除了我的最后一个字符从字符串(即UILabel文本)在IOS应用程序

@IBOutlet weak var labelText: UILabel! // Do Connection with UILabel

@IBAction func whenXButtonPress(_ sender: UIButton) { // Do Connection With X Button

    labelText.text = String((labelText.text?.dropLast())!) // Delete the last caracter and assign it

}

使用函数removeAtIndex(i: String.Index)

var s = "abc"    
s.removeAtIndex(s.endIndex.predecessor())  // "ab"

斯威夫特4.2

我还删除了我的最后一个字符从字符串(即UILabel文本)在IOS应用程序

@IBOutlet weak var labelText: UILabel! // Do Connection with UILabel

@IBAction func whenXButtonPress(_ sender: UIButton) { // Do Connection With X Button

    labelText.text = String((labelText.text?.dropLast())!) // Delete the last caracter and assign it

}

这是一个字符串扩展表单:

extension String {

    func removeCharsFromEnd(count_:Int) -> String {
        let stringLength = count(self)

        let substringIndex = (stringLength < count_) ? 0 : stringLength - count_

        return self.substringToIndex(advance(self.startIndex, substringIndex))
    }
}

对于Swift 1.2之前的版本:

...
let stringLength = countElements(self)
...

用法:

var str_1 = "Maxim"
println("output: \(str_1.removeCharsFromEnd(1))") // "Maxi"
println("output: \(str_1.removeCharsFromEnd(3))") // "Ma"
println("output: \(str_1.removeCharsFromEnd(8))") // ""

参考:

扩展向现有的类、结构或枚举类型添加新功能。这包括扩展您无法访问原始源代码的类型的能力(称为回溯建模)。扩展类似于Objective-C中的类别。(与Objective-C类别不同，Swift扩展没有名称。)

看文档

使用函数advance(startIndex, endIndex):

var str = "45+22"
str = str.substringToIndex(advance(str.startIndex, countElements(str) - 1))

一个快速变化的类别:

extension String {
    mutating func removeCharsFromEnd(removeCount:Int)
    {
        let stringLength = count(self)
        let substringIndex = max(0, stringLength - removeCount)
        self = self.substringToIndex(advance(self.startIndex, substringIndex))
    }
}

使用:

var myString = "abcd"
myString.removeCharsFromEnd(2)
println(myString) // "ab"