添加到父视图控制器时如何修复子视图不显示在子视图控制器中
How to fix subview not showing in child view controller when added to a parent view controller
我试图在 swift ios 应用程序中将子视图控制器添加到父视图控制器,但是当我添加子视图控制器时,activityIndicatorView
没有出现。我可能会错过什么?
这是一个可以在操场上尝试的片段:
import PlaygroundSupport
import Alamofire
class LoadingViewController: UIViewController {
private lazy var activityIndicator = UIActivityIndicatorView(style: .gray)
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(activityIndicator)
NSLayoutConstraint.activate([
activityIndicator.centerXAnchor.constraint(equalTo: view.centerXAnchor),
activityIndicator.centerYAnchor.constraint(equalTo: view.centerYAnchor)
])
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// We use a 0.5 second delay to not show an activity indicator
// in case our data loads very quickly.
DispatchQueue.main.asyncAfter(deadline: .now() + 0.0) { [weak self] in
self?.activityIndicator.startAnimating()
}
}
}
// methods for adding and removing child view controllers.
extension UIViewController {
func add(_ child: UIViewController, frame: CGRect? = nil) {
addChild(child)
if let frame = frame {
child.view.frame = frame
}
view.addSubview(child.view)
child.didMove(toParent: self)
}
func remove() {
// Just to be safe, we check that this view controller
// is actually added to a parent before removing it.
guard parent != nil else {
return
}
willMove(toParent: nil)
view.removeFromSuperview()
removeFromParent()
}
}
class MyViewController : UITabBarController {
override func loadView() {
let view = UIView()
view.backgroundColor = .white
let label = UILabel()
label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
label.text = "Hello World!"
label.textColor = .black
view.addSubview(label)
self.view = view
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let loadingViewController = LoadingViewController()
add(loadingViewController, frame: view.frame)
AF.request("http://www.youtube.com").response { response in
print(String(describing: response.response))
loadingViewController.remove()
}
}
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()
loadingViewController 视图填充了父视图,我尝试在不同的位置更改背景颜色并且有效。但是我尝试添加的 activityIndicator 或任何其他子视图都没有出现。
尝试添加行
activityIndicator.startAnimating()
在 LoadingViewController 的 viewDidLoad() 方法中 class
我试图在 swift ios 应用程序中将子视图控制器添加到父视图控制器,但是当我添加子视图控制器时,activityIndicatorView
没有出现。我可能会错过什么?
这是一个可以在操场上尝试的片段:
import PlaygroundSupport
import Alamofire
class LoadingViewController: UIViewController {
private lazy var activityIndicator = UIActivityIndicatorView(style: .gray)
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(activityIndicator)
NSLayoutConstraint.activate([
activityIndicator.centerXAnchor.constraint(equalTo: view.centerXAnchor),
activityIndicator.centerYAnchor.constraint(equalTo: view.centerYAnchor)
])
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// We use a 0.5 second delay to not show an activity indicator
// in case our data loads very quickly.
DispatchQueue.main.asyncAfter(deadline: .now() + 0.0) { [weak self] in
self?.activityIndicator.startAnimating()
}
}
}
// methods for adding and removing child view controllers.
extension UIViewController {
func add(_ child: UIViewController, frame: CGRect? = nil) {
addChild(child)
if let frame = frame {
child.view.frame = frame
}
view.addSubview(child.view)
child.didMove(toParent: self)
}
func remove() {
// Just to be safe, we check that this view controller
// is actually added to a parent before removing it.
guard parent != nil else {
return
}
willMove(toParent: nil)
view.removeFromSuperview()
removeFromParent()
}
}
class MyViewController : UITabBarController {
override func loadView() {
let view = UIView()
view.backgroundColor = .white
let label = UILabel()
label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
label.text = "Hello World!"
label.textColor = .black
view.addSubview(label)
self.view = view
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let loadingViewController = LoadingViewController()
add(loadingViewController, frame: view.frame)
AF.request("http://www.youtube.com").response { response in
print(String(describing: response.response))
loadingViewController.remove()
}
}
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()
loadingViewController 视图填充了父视图,我尝试在不同的位置更改背景颜色并且有效。但是我尝试添加的 activityIndicator 或任何其他子视图都没有出现。
尝试添加行
activityIndicator.startAnimating()
在 LoadingViewController 的 viewDidLoad() 方法中 class