Ios 需要基于URLSession（Swift3）中的数据运行动画的帮助吗

我在这里束手无策。我已经尝试了我能想到的一切，但无法让它发挥作用

我觉得我在这里要做的应该很简单——但斯威夫特让这件事变得非常困难，我感到沮丧

最后，我要做的就是从web脚本中获取一段数据（它将返回一个浮点），然后使用该浮点设置UIView的动画

因此，为了简单起见，我们假设web脚本返回“50.0”。然后我想取这个数字，并设置UIView的动画，使其从0px到50px高

我已经读到，您无法从异步任务中获取数据，并且您基本上必须运行希望在闭包中使用该数据运行的任何任务。然而。。。当我尝试在闭包中运行动画时，Xcode拍打我的手腕，告诉我我正在尝试在不同的线程中修改AutoLayout属性。那我该怎么办

以下是我的代码，请尽我所能对其进行注释：

首先，我的ViewController中有一个紫色背景的UIView。我在这个UIView中添加了一个子视图，它是绿色的，并且将根据web脚本的返回值垂直增长，有效地生成一个“米”（见图）

---

在iOS中，您不能在后台线程上更新UI。要更新UI，请在主线程中编写代码，如下所示：

    DispatchQueue.main.async{
      //update your UI here 
    }

private func getMeterHeight(deviceID: String) {

    guard let URL = URL(string: "http://www.mywebsite.com/getLatestReading.php") else {return}
    let request = NSMutableURLRequest(url: URL)

    request.httpMethod = "POST"

    request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")

    let bodyObject: [String: String] = [
    "deviceID": deviceID
    ]

    request.httpBody = try! JSONSerialization.data(withJSONObject: bodyObject, options: [])
    var responseString: NSString = ""

    let task = URLSession.shared.dataTask(with: request as URLRequest) {
    data, response, error in

     if (error == nil) {
        responseString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!

        //This is the value that I need to get out of this unescapable black hole
        let oilMeterHeight = 175 * responseString.doubleValue;

         DispatchQueue.main.async{
          //update your UI here 
           UIView.transition(with: self.oilReading, duration: 1.0, animations: {self.oilReading.frame = CGRect(x: self.tankRep.bounds.origin.x, y: CGFloat(self.tankRep.bounds.height - CGFloat(oilMeterHeight)), width: 100, height: CGFloat(oilMeterHeight))}, completion: nil)

        }
     } else {
        // Failure
        print("URL Session Task Failed: %@", error!.localizedDescription);
    }
}

task.resume()
    }

在您的情况下，要使用web服务响应中的值get设置视图动画，请在获取结果后编写此块。如果api调用一切正常，则getMeterHeight方法应如下所示：

    DispatchQueue.main.async{
      //update your UI here 
    }

private func getMeterHeight(deviceID: String) {

    guard let URL = URL(string: "http://www.mywebsite.com/getLatestReading.php") else {return}
    let request = NSMutableURLRequest(url: URL)

    request.httpMethod = "POST"

    request.addValue("application/json; charset=utf-8", forHTTPHeaderField: "Content-Type")

    let bodyObject: [String: String] = [
    "deviceID": deviceID
    ]

    request.httpBody = try! JSONSerialization.data(withJSONObject: bodyObject, options: [])
    var responseString: NSString = ""

    let task = URLSession.shared.dataTask(with: request as URLRequest) {
    data, response, error in

     if (error == nil) {
        responseString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)!

        //This is the value that I need to get out of this unescapable black hole
        let oilMeterHeight = 175 * responseString.doubleValue;

         DispatchQueue.main.async{
          //update your UI here 
           UIView.transition(with: self.oilReading, duration: 1.0, animations: {self.oilReading.frame = CGRect(x: self.tankRep.bounds.origin.x, y: CGFloat(self.tankRep.bounds.height - CGFloat(oilMeterHeight)), width: 100, height: CGFloat(oilMeterHeight))}, completion: nil)

        }
     } else {
        // Failure
        print("URL Session Task Failed: %@", error!.localizedDescription);
    }
}

task.resume()
    }