ios - 如何在 iOS 11 中实现音量快门？

Question

我想在我的相机应用中实现音量快门。当用户按下音量按钮时，我应该得到一个事件来拍照。

我正在寻找满足以下要求的实现:

• 即使音量当前处于最大并且用户按下音量增大按钮，它也应该可以工作。
• 不应有显示音量已更改的屏幕 UI。
• 应该没有已知的 Apple 拒绝使用此技术的应用程序的案例。

关于此主题存在其他问题和答案，但适用于旧版本的 iOS，因此我想找到适用于 iOS 11 的问题和答案。

ProCamera、ProCam 和 Camera+ 等相机应用具有满足所有这些条件的音量快门，因此这显然是可能的。

Answer 1

下面是满足您所有要求的代码——不过我不确定 Apple 是否会批准。
我从 StackOverflow 上的问题/答案中提取了所有这些代码。

Tested with iOS 10.2 in Xcode 8.3.1

您需要使用 AVFoundation 和 MediaPlayer 框架才能正常工作。

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程序后仍然有效，请在应用程序激活时使用 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")
    }
}

View Controller

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")
    }
}