键入动画：删除字符 [英] Typing animation: deleting characters

问题描述

这是一个打字动画，它以固定的时间间隔将数组中的字符添加到文本字段的文本中：

Here's a typing animation that adds up characters from an Array to the text of a text field at a fixed time interval:

@IBOutlet weak var textFieldMain: UITextField!
var myText = Array("Hi! I'm Cesare.".characters)
var myString = "Hi! I'm Cesare."
var typingAnimationCounter = 0
var typingAnimationTimer: NSTimer?

func fireTimer() {
    typingAnimationTimer = NSTimer.scheduledTimerWithTimeInterval(0.05, target: self, selector: "typeLetter", userInfo: nil, repeats: true)
}

func typeLetter() {
    if typingAnimationCounter < myText.count {
        textFieldMain.text = textFieldMain.text! + String(myText[typingAnimationCounter])
        typingAnimationTimer?.invalidate()
        typingAnimationTimer = NSTimer.scheduledTimerWithTimeInterval(0.15, target: self, selector: "typeLetter", userInfo: nil, repeats: false)
    } else {
        typingAnimationTimer?.invalidate()
    }
    typingAnimationCounter++
}

我想现在删除textField的字符（就好像它是一个打字动画，但删除字符）。我不明白怎么做。

I would like to have characters of the textField deleted now (like if it was a typing animation, but by deleting characters). I can't figure out how, though.

func fireDeletionTimer() {
    typingAnimationTimer = NSTimer.scheduledTimerWithTimeInterval(0.45, target: self, selector: "deleteLetter", userInfo: nil, repeats: true)
}

func deleteLetter() {
    if typingAnimationCounter < myText.count - 1 {
        let index = myString.characters.count - typingAnimationCounter - 1
        textFieldMain.text = myString.stringByReplacingOccurrencesOfString(String(myText[index]), withString: "", options: NSStringCompareOptions.LiteralSearch, range: nil)
        typingAnimationTimer?.invalidate()
        typingAnimationTimer = NSTimer.scheduledTimerWithTimeInterval(0.45, target: self, selector: "deleteLetter", userInfo: nil, repeats: false)
    } else {
        typingAnimationTimer?.invalidate()
    }
    typingAnimationCounter++
}

我想用空字符串替换每个字符，但它不起作用（字符串的随机字母被替换）。如何修复我的代码？

I thought of replacing every single character with an empty String, but it doesn't work (random letters of the string are replaced). How can I fix my code?

推荐答案

为什么不执行以下操作：

Why not do the following:

func deleteLetter() {
    if textFieldMain.text != "" {
        textFieldMain.text = str.substringToIndex(textFieldMain.text.endIndex.predecessor())
    } else {
       typingAnimationTimer?.invalidate()
    }
}

顺便说一句，如果你在 fireDeletionTimer（）中用重复：真启动你的计时器，你不需要再次重新创建它再次在 deleteLetter（）

By the way, if you start your timer with "repeats: true" in fireDeletionTimer() you don't need to recreate it again and again in deleteLetter()

此外， stringByReplacingOccurrencesOfString（）清除文本中该字母的每个实例，而不仅仅是最后一个。

Also, stringByReplacingOccurrencesOfString() clears every instance of that letter in your text, not just the last one.

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