ios – 更新UILabel.text很慢

现在,我的视图控制器正在做一些非常简单的事情：

>呼叫Web服务
>打印一个值
>将UILabel的文本值设置为该值

1& 2非常活泼.第三步需要大约10秒才能在模拟器中显示在屏幕上.

switch currentTemp {
    case 80..<180:
        self.riskType.text = "Heat Index:"
        self.perceivedTemperatureValue.text = "\(currentHeatIndex)"
    case -100..<50:
        self.riskType.text = "Wind Chill:"
        self.perceivedTemperatureValue.text = "\(currentWindChill)"
    default:
        self.riskType.text = "Temperature:"
        println(currentTemp)
        self.perceivedTemperatureValue.text = "\(currentTemp)"
    }

知道为什么这么慢吗？在打印值时,是否还需要执行其他操作才能使更改出现？

您发布的代码中没有太多内容,但听起来您在Web服务回调中直接进行标签更新,这通常在后台线程上运行.所有UI工作都需要在主线程上完成,否则你将遇到这样的问题.如果是这样,使用GCD的dispatch_async在主线程上运行该switch语句将解决您的问题：

dispatch_async(dispatch_get_main_queue()) {
    switch currentTemp {
    case 80..<180:
        self.riskType.text = "Heat Index:"
        self.perceivedTemperatureValue.text = "\(currentHeatIndex)"
    case -100..<50:
        self.riskType.text = "Wind Chill:"
        self.perceivedTemperatureValue.text = "\(currentWindChill)"
    default:
        self.riskType.text = "Temperature:"
        println(currentTemp)
        self.perceivedTemperatureValue.text = "\(currentTemp)"
    }
}