所以这里的代码可以满足你的所有要求——不过我不确定 Apple 是否会批准它。
我已经从 StackOverflow 上的问题/答案中提取了所有这些代码。
在 Xcode 8.3.1 中使用 iOS 10.2 测试
您需要使用AVFoundation 和MediaPlayer 框架才能使其工作。
import UIKit
import AVFoundation
import MediaPlayer
class ViewController: UIViewController {
//keeps track of the initial volume the user had set when entering the app
//used to reset the volume when he exits the app
var volume: Float = 0
override func viewDidLoad() {
super.viewDidLoad()
let audioSession = AVAudioSession.sharedInstance()
volume = audioSession.outputVolume-0.1 //if the user is at 1 (full volume)
try! audioSession.setActive(true)
audioSession.addObserver(self, forKeyPath: "outputVolume", options: NSKeyValueObservingOptions.new, context: nil)
//prevents the volume hud from showing up
let volView = MPVolumeView(frame: .zero)
view.addSubview(volView)
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
//when the user changes the volume,
//prevent the output volume from changing by setting it to the default volume we specified,
//so that we can continue pressing the buttons for ever
(MPVolumeView().subviews.filter{NSStringFromClass($0.classForCoder) == "MPVolumeSlider"}.first as? UISlider)?.setValue(volume, animated: false)
//implement your photo-capturing function here
print("volume changed")
}
}
更新
如果您想确保您的代码在用户退出应用后仍然有效，请在应用激活时使用 AppDelegate 安装观察者，如下所示：
AppDelegate
import UIKit
import AVFoundation
import MediaPlayer
var volume: Float = 0.5
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
var window: UIWindow?
let audioSession = AVAudioSession.sharedInstance()
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
return true
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
(MPVolumeView().subviews.filter{NSStringFromClass($0.classForCoder) == "MPVolumeSlider"}.first as? UISlider)?.setValue(volume, animated: false)
NotificationCenter.default.removeObserver(self)
NotificationCenter.default.post(Notification(name: Notification.Name(rawValue: "volumeChanged")))
}
func applicationDidBecomeActive(_ application: UIApplication) {
volume = audioSession.outputVolume
if volume == 0 { volume += 0.1 } else if volume == 1 { volume -= 0.1 }
try! audioSession.setActive(true)
audioSession.addObserver(self, forKeyPath: "outputVolume", options: NSKeyValueObservingOptions.new, context: nil)
}
func applicationWillResignActive(_ application: UIApplication) {
audioSession.removeObserver(self, forKeyPath: "outputVolume")
}
}
视图控制器
import UIKit
import AVFoundation
import MediaPlayer
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(self.volumeChanged), name: Notification.Name(rawValue: "volumeChanged"), object: nil)
//prevents the volume hud from showing up
let volView = MPVolumeView(frame: .zero)
view.addSubview(volView)
}
func volumeChanged() {
print("volume changed")
}
}