背景Xcode版本8.2（8C38）
适用于iPhone 7 plus的ios 10.2 - 模拟器
我让它在objective-c中工作，我现在试图让它在swift中工作。代码编译并运行，但单击按钮时标签不会更改。如果标签正在更新，我会将其发布在CR而不是此处。
它最初是作为一个采访带回家的问题，但是目标c部分让我接受了现场采访。我正在追求这一点，以了解更多有关斯威夫特的信息。面试问题
/*
* Create a static library or iOS Framework using Objective-C that performs the following 3 functions:
* - Collects the GPS location (latitude and longitude) of the user at a point in time
* - Collects the battery state and returns whether or not the device is plugged in and what percentage of life is left.
* - Accesses any publicly available, free API to collect the data of your choice and returns it
* (this should be a network call)
*
* Build a simple application with 3 buttons and a label where text can be displayed. Each button should call into the
* three functions of the library described above and output the response to the label. Your application should consist
* of two tabs, one written in Objective-C and one written in Swift. Both tabs should call into the same Objective-C
* library and perform the same function.
*
* Only use Apple frameworks to complete this task. Fully comment your code explaining your logic and choices where multiple
* choices are available. For example, Apple provides numerous ways to retrieve a network resource, document why you choose
* the solution you did.
*/
这可能是一个重复的问题，但我不确定我是否已经查看过 以下问题：
我不确定问题出在我所做的异步调用中，是在创建按钮本身，还是在顶部的属性/ var声明中。
import UIKit
class ViewController: UIViewController {
var getGPSLongitudeAndLatitudeWithTimeStamp : UIButton?
var getBatteryLevelAndState : UIButton?
var getNextorkImplementation : UIButton?
var displayButtonAction : UILabel?
// The following variables are used in multiple functions. They are constant during the display of the super view
// and control the size of the subviews
var selfWidth : CGFloat = 0.0
var buttonHeight : CGFloat = 0.0
var viewElementWidth : CGFloat = 0.0
var buttonYCenterOffset : CGFloat = 0.0 // The y center should be half the value of the height
var buttonXCenter : CGFloat = 0.0 // Center the button title relative to the width of the button and the width of the super view
var buttonXInit : CGFloat = 0.0
var buttonVerticalSeparation : CGFloat = 0.0
var startingVerticalLocation : CGFloat = 0.0
var displayLabelHeight: CGFloat = 50.0
func initFramingValuesOfMyDisplay() {
selfWidth = self.view.bounds.size.width
buttonHeight = 20.0 // This should be programmable in relative to self.view.bounds.size.height
viewElementWidth = 0.8 * selfWidth;
buttonYCenterOffset = buttonHeight / 2.0; // The y center should be half the value of the height
buttonXCenter = selfWidth / 2.0; // Center the button title relative to the width of the button and the width of the super view
buttonXInit = 0.0;
buttonVerticalSeparation = buttonHeight + buttonYCenterOffset;
startingVerticalLocation = 430.0; // 430 was chosen based on experimentation in the simulator
}
func setLabelWithGPSLatitudeAndLongitudeWithTimeStampData()
{
var actionString : String = "Testing Label Text"
actionString = "GPS Button Action Failure: Data Model not created";
DispatchQueue.global().async {
self.displayButtonAction?.text = actionString
}
}
func setLabelWithBatteryLevelAndState() {
var actionString : String = "Get Battery Level and State";
actionString = "Battery Button Action Failure: Data Model not created"
DispatchQueue.global().async {
self.displayButtonAction?.text = actionString
}
}
func setLabelActionNetwork() {
var actionString :String = "Fake Button set to American Express Stock Price";
actionString = "Network Button Action Failure: Data Model not created";
DispatchQueue.global().async {
self.displayButtonAction?.text = actionString
}
}
func makeAButton(yButtonStart : CGFloat, buttonTitle: String, underSubview: UIButton?) -> UIButton
{
let thisButton = UIButton.init(type: .system)
thisButton.frame = CGRect(x: buttonXInit, y: yButtonStart, width: viewElementWidth, height: buttonHeight)
thisButton.setTitle(buttonTitle, for:UIControlState.normal)
thisButton.backgroundColor = UIColor.yellow
thisButton.setTitleColor(UIColor.black, for: UIControlState.normal)
if ((underSubview) == nil) {
self.view.addSubview(thisButton)
}
else {
self.view.insertSubview(thisButton, belowSubview:underSubview!)
}
return thisButton;
}
func makeALabel(yLabelStart : CGFloat, underSubview: UIButton?) -> UILabel
{
let thisLabel = UILabel.init()
thisLabel.frame = CGRect(x: selfWidth * 0.1, y: yLabelStart, width: viewElementWidth, height: displayLabelHeight)
thisLabel.font = thisLabel.font.withSize(12)
thisLabel.lineBreakMode = .byWordWrapping;
thisLabel.numberOfLines = 0;
thisLabel.textAlignment = NSTextAlignment.center;
thisLabel.textColor = UIColor.black;
if ((underSubview) == nil) {
self.view.addSubview(thisLabel)
}
else {
self.view.insertSubview(thisLabel, belowSubview:underSubview!)
}
return thisLabel;
}
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
self.view.backgroundColor = UIColor.white
initFramingValuesOfMyDisplay()
addButtonAndLabels()
}
func addButtonAndLabels() -> Void {
if (selfWidth < 1.0) {
return;
}
var viewElementVerticalLocation: CGFloat = startingVerticalLocation;
// var touchUpInside : UIControlEvents = touchUpInside;
let getGPSLongitudeAndLatitudeWithTimeStamp : UIButton = makeAButton(yButtonStart: viewElementVerticalLocation, buttonTitle: "Get GPS Location with TimeStamp", underSubview: nil)
getGPSLongitudeAndLatitudeWithTimeStamp.addTarget(self, action: #selector(setLabelWithGPSLatitudeAndLongitudeWithTimeStampData), for: .touchUpInside)
viewElementVerticalLocation += buttonVerticalSeparation
let getBatteryLevelAndState : UIButton = makeAButton(yButtonStart: viewElementVerticalLocation, buttonTitle: "Get Battery Level and State", underSubview: getGPSLongitudeAndLatitudeWithTimeStamp)
getBatteryLevelAndState.addTarget(self, action: #selector(setLabelWithBatteryLevelAndState), for: .touchUpInside)
viewElementVerticalLocation += buttonVerticalSeparation
let getNextorkImplementation : UIButton = makeAButton(yButtonStart: viewElementVerticalLocation, buttonTitle: "Get Battery Level and State", underSubview: getBatteryLevelAndState)
getNextorkImplementation.addTarget(self, action: #selector(setLabelWithBatteryLevelAndState), for: .touchUpInside)
viewElementVerticalLocation += buttonVerticalSeparation
let displayButtonAction = makeALabel(yLabelStart: viewElementVerticalLocation, underSubview: getNextorkImplementation)
displayButtonAction.text = "No Action Yet"
}
required init(coder aDecoder: NSCoder) {
super.init(nibName: nil, bundle: nil)
initFramingValuesOfMyDisplay()
}
}
答案 0 :(得分：3)
您的displayButtonAction实际上是零。请注意，在您的方法addButtonAndLabels()中，您正在创建一个标签，并仅在该方法的范围内填充文本：
let displayButtonAction = makeALabel(yLabelStart: viewElementVerticalLocation, underSubview: getNextorkImplementation)
在makeALabel方法中，您将该标签作为视图的子视图插入，这就是运行应用程序时显示的原因。您无处将该标签分配给displayButtonAction。
总之，您要创建一个本地范围UILabel，填充它的占位符文本，将其作为视图的子视图插入，然后丢弃它，然后尝试填充displayButtonAction标签的文本按下按钮为nil。
在addButtonAndLabels()内，通过以下方式将实例化标签分配给视图控制器主范围内的主标签：
self.displayButtonAction = displayButtonAction
将帮助您开始正确的方向。
在这种情况下，使用调试工具，断点和po是您的朋友。
答案 1 :(得分：2)
我注意到的主要是你试图在后台队列上设置标签的文本。除了主队列之外，您不应该对除了主队列之外的任何内容进行UI更改，因此将其更改为主队列，如下所示：
DispatchQueue.main.async {
self.displayButtonAction?.text = actionString
}
您应该在调试器中收到警告，告诉您这一点。
你还应该在该函数中抛出一个断点来验证displayButtonAction不是nil，并且它有frame实际上在屏幕上且大小非零。充分利用这个调试器。
答案 2 :(得分：1)
您无法在后台（异步）线程上更新UI元素。您需要获取主线程才能执行此操作。
DispatchQueue.main.async(execute: {
self.label.text = "some text"
})