在学习 Swift 的同时,我编写了一个简单的练习 iOS 应用程序来从网站上抓取给定城市的天气信息并将其显示在 UILabel 中。
该代码使用“NSURLSession.sharedSession().dataTaskWithURL”闭包。虽然我能够正确获取数据并捕获“UILabel.text”中的相关文本,但我无法让实际应用显示更新后的 UILabel。
我做错了什么?相关代码如下:
@IBAction func buttonPressed(sender: AnyObject) {
var urlString = "http://www.weather-forecast.com/locations/" + cityName.text.stringByReplacingOccurrencesOfString(" ", withString: "") + "/forecasts/latest"
var url = NSURL(string: urlString)
let task = NSURLSession.sharedSession().dataTaskWithURL(url) {(data, response, error) in
var urlContent = NSString(data: data, encoding: NSUTF8StringEncoding) as String
var contentArray = urlContent.componentsSeparatedByString("<span class=\"phrase\">")
var weatherInfo = contentArray[1].componentsSeparatedByString("</span>")
self.resultShow.text = weatherInfo[0] // Text does not show in the app
println(weatherInfo[0]) // This works correctly
println(self.resultShow.text) // This works correctly
}
task.resume()
}
最佳答案
您需要在主线程上执行您的 UI 更新
NSURLSession
完成处理程序将始终在后台线程上调用。要更新您的 UI,一个简单的 dispatch_async
到主线程就足够了:)
@IBAction func buttonPressed(sender: AnyObject) {
var urlString = "http://www.weather-forecast.com/locations/" + cityName.text.stringByReplacingOccurrencesOfString(" ", withString: "") + "/forecasts/latest"
var url = NSURL(string: urlString)
let task = NSURLSession.sharedSession().dataTaskWithURL(url) {(data, response, error) in
var urlContent = NSString(data: data, encoding: NSUTF8StringEncoding) as String
var contentArray = urlContent.componentsSeparatedByString("<span class=\"phrase\">")
var weatherInfo = contentArray[1].componentsSeparatedByString("</span>")
dispatch_async(dispatch_get_main_queue(), {
//perform all UI stuff here
self.resultShow.text = weatherInfo[0]
})
}
task.resume()
}
编辑
虽然这里不重要,因为没有保留闭包,但在某些情况下它很重要 explicitly declare capture lists to avoid retain cycles .
关于ios - 在 Swift 闭包内更新的 UILabel 文本拒绝显示,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/26262398/