project 4 reviewed

CameraViewController 中没有用到 UIGestureRecognizerDelegate 中的方法。相关声明和
delegate 赋值可以去掉。
didPressTakeAnother
方法，改为didTouchScreen更合适，因为里面要处理两种case，TakeAnother不能涵盖函数的功能，也不够明确。
另外里面没有必要调用captureSession.startRunning()。
didPressTakePhoto改为takePhoto。拍摄照片和触发拍摄的操作没有关系，不需要在函数名中体现press。
AVCaptureSession应该在需要时才启动。长时间开启摄像头会增加耗电，让设备发热，影响摄像头寿命。

Author: Martin-Lv

Project 04 - SnapChatMenu/Snapchat Menu/CameraViewController.swift

@@ -9,7 +9,7 @@
 import UIKit
 import AVFoundation
 
-class CameraViewController: UIViewController, UIGestureRecognizerDelegate {
+class CameraViewController: UIViewController {
 
     @IBOutlet private weak var cameraView: UIView!
     @IBOutlet private weak var tempImageView: UIImageView!
@@ -20,29 +20,42 @@ class CameraViewController: UIViewController, UIGestureRecognizerDelegate {
 
     private var didTakePhoto = false
 
+    var showing = false{
+        willSet {
+            if newValue == showing {
+                return
+            }
+            if newValue {
+                captureSession.startRunning()
+                print("start running")
+            }else{
+                captureSession.stopRunning()
+                print("stop running")
+            }
+        }
+    }
+    
     override func viewDidLoad() {
         super.viewDidLoad()
         configRecognizer()
         configCamera()
     }
 
     private func configRecognizer() {
-        let gesture = UITapGestureRecognizer.init(target: self, action: #selector(didPressTakeAnother))
-        gesture.delegate = self
+        let gesture = UITapGestureRecognizer.init(target: self, action: #selector(didTouchScreen))
         view.addGestureRecognizer(gesture)
     }
 
-    func didPressTakeAnother() {
+    func didTouchScreen() {
         if !isCameraAvailable() {
             return
         }
         if didTakePhoto {
             tempImageView.isHidden = true
             didTakePhoto = false
         } else {
-            captureSession.startRunning()
             didTakePhoto = true
-            didPressTakePhoto()
+            takePhoto()
         }
     }
 
@@ -70,10 +83,9 @@ class CameraViewController: UIViewController, UIGestureRecognizerDelegate {
         previewLayer.videoGravity = AVLayerVideoGravityResizeAspect
         previewLayer.connection.videoOrientation = AVCaptureVideoOrientation.portrait
         cameraView.layer.addSublayer(previewLayer)
-        captureSession.startRunning()
     }
 
-    private func didPressTakePhoto() {
+    private func takePhoto() {
         guard let videoConnection = stillImageOutput.connection(withMediaType: AVMediaTypeVideo) else {
             return
         }

Project 04 - SnapChatMenu/Snapchat Menu/ViewController.swift

@@ -8,9 +8,10 @@
 
 import UIKit
 
-class ViewController: UIViewController {
+class ViewController: UIViewController, UIScrollViewDelegate {
 
     @IBOutlet weak var scrollView: UIScrollView!
+    var cameraViewController: CameraViewController!
 
     override var prefersStatusBarHidden: Bool {
         return true
@@ -23,7 +24,7 @@ class ViewController: UIViewController {
 
     private func configScrollView() {
         let leftViewController: LeftViewController = LeftViewController(nibName: "LeftViewController", bundle: nil)
-        let cameraViewController: CameraViewController = CameraViewController(nibName: "CameraViewController", bundle: nil)
+        cameraViewController = CameraViewController(nibName: "CameraViewController", bundle: nil)
         let rightViewController: RightViewController = RightViewController(nibName: "RightViewController", bundle: nil)
 
         addChildViewController(leftViewController)
@@ -43,6 +44,15 @@ class ViewController: UIViewController {
         itemFrame.origin.x = 2 * view.frame.width
         rightViewController.view.frame = itemFrame
         scrollView.contentSize = CGSize(width: view.frame.width * 3, height: view.frame.size.height)
+        scrollView.delegate = self
+    }
+    
+    func scrollViewDidScroll(_ scrollView: UIScrollView) {
+        let offsetX = scrollView.contentOffset.x
+        let cameraViewShowing = offsetX > 0 && offsetX < view.frame.width * 2
+        if cameraViewShowing != cameraViewController.showing {
+            cameraViewController.showing = cameraViewShowing
+        }
     }
 
 }