Question

我的应用程序中有一个视图控制器，我用它来进行调试，以显示应用程序的一些内部结构（仅适用于本地xcode版本，应用程序商店版本没有此控制器）。

在这个控制器中，我有一个标签，我想反映内部组件的状态（具体来说，我希望它显示该组件是启用还是禁用）。

我的问题：

＃1：将UILabel的.attributedText属性设置为与以前相同的值是否很昂贵，还是应该缓存旧值并仅在更改时设置属性？ /强>

＃2：.text（非归因）属性怎么样？

我目前正在使用以下代码：

// Schedule timer to update the control panel. (This is debug-only, so not worth // the complexity of making this event-based) Timer.scheduledTimer(withTimeInterval: 0.5, repeats: true) { [weak self] timer in DispatchQueue.main.async { // Stop timer if we've been dealloced or are no longer being presented guard let strongSelf = self, strongSelf.isBeingPresented else { timer.invalidate() return } // "Something Enabled / Disabled" label let somethingIsEnabled = strongSelf.someDepenency.isEnabled let somethingEnabledString = NSMutableAttributedString(string: "Something ") somethingEnabledString.append(NSAttributedString(string: isEnabled ? "Enabled" : "Disabled", attributes: isEnabled ? nil : [NSForegroundColorAttributeName: UIColor(xtHardcodedHexValue: "0xCD0408")])) strongSelf.somethingEnabledLabel?.attributedText = somethingEnabledString } }

Answer 1

在我分享一些数字之前，我强烈建议不要执行此类过早优化。请考虑以下代码：

private func getAttributedString() -> NSMutableAttributedString{ let attributedString = NSMutableAttributedString(string: "Something ") attributedString.append(NSAttributedString(string: "Enabled", attributes: [NSForegroundColorAttributeName: UIColor(rgb: 0xCD0408)])) return attributedString } //overwrites attributed text 100000 times @IBAction func overwriteAttributedText(_ sender: Any) { let timeBeforeAction = Date.init() print ("Time taken to overwrite attributed text is ") for _ in 1 ... 100000{ label.attributedText = getAttributedString() } let timeAfterAction = Date.init() let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction) print(timeTaken) } //overwrites attributed text 100 times @IBAction func cacheAttributedText(_ sender: Any) { let timeBeforeAction = Date.init() print ("Time taken to selectively overwrite attributed text is ") for i in 1 ... 100000{ if i % 1000 == 0 { label.attributedText = getAttributedString() } } let timeAfterAction = Date.init() let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction) print(timeTaken) } //overwrites text 100000 times @IBAction func overWriteText(_ sender: Any) { let defaultText = "Hello World" let timeBeforeAction = Date.init() print ("Time taken to overwrite text is ") for _ in 1 ... 100000{ label.text = defaultText } let timeAfterAction = Date.init() let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction) print(timeTaken) }

结果如下：

Time taken to overwrite attributed text is 0.597925961017609 Time taken to selectively overwrite attributed text is 0.004891037940979 Time taken to overwrite text is 0.0462920069694519

结果不言而喻，但如果需要进行这样的优化，我就把它留给你。

Answer 2

虽然7to4在过早优化方面是正确的，但他使用的演示代码具有误导性。 .attributedText setter本身实际上比设置.text更快;创建属性字符串是瓶颈。这是他的代码的修改版本，其中包含预先缓存属性字符串的方法：

private func getAttributedString() -> NSMutableAttributedString{
    let attributedString = NSMutableAttributedString(string: "Something ")
    attributedString.append(NSAttributedString(string: "Enabled",
                                               attributes:  [NSAttributedStringKey.foregroundColor: UIColor.red]))
    return attributedString
}

//overwrites attributed text 100000 times
@IBAction func overwriteAttributedText(_ sender: Any) {
    let timeBeforeAction = Date.init()
    print ("Time taken to overwrite attributed text is ")
    for _ in 1 ... 100000{
        label.attributedText = getAttributedString()
    }
    let timeAfterAction = Date.init()
    let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction)
    print(timeTaken)
}

//overwrites attributed text 100000 times with a cached string
@IBAction func overwriteAttributedTextWithCachedString(_ sender: Any) {
    let timeBeforeAction = Date.init()
    let attributedString = getAttributedString()
    print ("Time taken to overwrite attributed text with cached string is ")
    for _ in 1 ... 100000{
        label.attributedText = attributedString
    }
    let timeAfterAction = Date.init()
    let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction)
    print(timeTaken)
}

//overwrites text 100000 times
@IBAction func overWriteText(_ sender: Any) {
    let defaultText = "Hello World"
    let timeBeforeAction = Date.init()
    print ("Time taken to overwrite text is ")
    for _ in 1 ... 100000{
        label.text = defaultText
    }
    let timeAfterAction = Date.init()
    let timeTaken = timeAfterAction.timeIntervalSince(timeBeforeAction)
    print(timeTaken)
}

结果：

Time taken to overwrite attributed text is 
0.509455919265747
Time taken to overwrite attributed text with cached string is 
0.0451710224151611
Time taken to overwrite text is 
0.0634149312973022

平均而言，.attributedText setter本身比.text setter快30~40％。也就是说，注意它可能需要很多标签才能真正成为瓶颈。还要记住（如果遇到一些疯狂的情况）这是你的瓶颈，这种优化只有在事先预先分配了属性字符串时才有效。

将UILabel.attributedText设置为相同的值是否昂贵？

2 个答案: