Swift - RxSwift的使用详解59（DelegateProxy样例2：图片选择功能）

作者：hangge | 2018-05-11 08:10

接下来介绍的同样是 RxSwift 的官方样例，演示的是如何对 UIImagePickerControllerDelegate 进行 Rx 封装，方便我们在 RxSwift 项目中选择图片（可以通过拍照、或者从相簿中选取）

三、从本地相册、或摄像头获取图片

1，效果图

（1）点击“拍照”按钮，会打开摄像头进行拍照，拍照后自动将照片显示在下方的 imageView 中。

（2）而点击“选择照片”或“选择照片并裁剪”按钮后，会打开本地相册选择照片，选择后自动将照片显示在下方的 imageView 中。不过后者在选择完毕后还多了个编辑步骤，可以把照片裁剪成正方形再显示。

2，准备工作

（1）RxImagePickerDelegateProxy.swift

首先我们继承 DelegateProxy 创建一个关于图片选择的代理委托，同时它还要遵守 DelegateProxyType、UIImagePickerControllerDelegate、UINavigationControllerDelegate 协议。

import RxSwift
import RxCocoa
import UIKit

//图片选择控制器（UIImagePickerController）代理委托
public class RxImagePickerDelegateProxy :
    DelegateProxy<UIImagePickerController,
     UIImagePickerControllerDelegate & UINavigationControllerDelegate>,
    DelegateProxyType,
    UIImagePickerControllerDelegate,
    UINavigationControllerDelegate {
    
    public init(imagePicker: UIImagePickerController) {
        super.init(parentObject: imagePicker,
                   delegateProxy: RxImagePickerDelegateProxy.self)
    }
    
    public static func registerKnownImplementations() {
        self.register { RxImagePickerDelegateProxy(imagePicker: $0) }
    }
    
    public static func currentDelegate(for object: UIImagePickerController)
        -> (UIImagePickerControllerDelegate & UINavigationControllerDelegate)? {
            return object.delegate
    }
    
    public static func setCurrentDelegate(_ delegate: (UIImagePickerControllerDelegate
        & UINavigationControllerDelegate)?, to object: UIImagePickerController) {
        object.delegate = delegate
    }
}

（2）UIImagePickerController+Rx.swift

接着我们对 UIImagePickerController 进行 Rx 扩展，作用是将 UIImagePickerController 与前面创建的代理委托关联起来，将图片选择相关的 delegate 方法转为可观察序列。

注意：下面代码中将 methodInvoked 方法替换成 sentMessage 其实也可以，它们的区别可以看我的另一篇文章：

Swift - RxSwift的使用详解61（sendMessage和methodInvoked的区别）

import RxSwift
import RxCocoa
import UIKit

//图片选择控制器（UIImagePickerController）的Rx扩展
extension Reactive where Base: UIImagePickerController {
    
    //代理委托
    public var pickerDelegate: DelegateProxy<UIImagePickerController,
        UIImagePickerControllerDelegate & UINavigationControllerDelegate > {
        return RxImagePickerDelegateProxy.proxy(for: base)
    }
    
    //图片选择完毕代理方法的封装
    public var didFinishPickingMediaWithInfo: Observable<[String : AnyObject]> {
        
        return pickerDelegate
            .methodInvoked(#selector(UIImagePickerControllerDelegate
                .imagePickerController(_:didFinishPickingMediaWithInfo:)))
            .map({ (a) in
                return try castOrThrow(Dictionary<String, AnyObject>.self, a[1])
            })
    }
    
    //图片取消选择代理方法的封装
    public var didCancel: Observable<()> {
        return pickerDelegate
            .methodInvoked(#selector(UIImagePickerControllerDelegate
                .imagePickerControllerDidCancel(_:)))
            .map {_ in () }
    }
}

//转类型的函数（转换失败后，会发出Error）
fileprivate func castOrThrow<T>(_ resultType: T.Type, _ object: Any) throws -> T {
    guard let returnValue = object as? T else {
        throw RxCocoaError.castingError(object: object, targetType: resultType)
    }
    return returnValue
}

3，使用样例

（1）要获取照片或者进行拍照，首先我们需要在 info.plist 里加入相关的描述：

Privacy - Camera Usage Description：App 需要访问您的相机
Privacy - Photo Library Usage Description：App 需要访问您的照片

（2）Main.storyboard

在 StoryBoard 中添加 3 个 Button 以及 1 个 ImageView，并将它们与代码做 @IBOutlet 绑定。

（3）ViewController.swift

主视图控制器代码如下，可以看到原来图片选择完毕这个代理方法现在已经变成响应式的了。

import UIKit
import RxSwift
import RxCocoa

class ViewController: UIViewController {
    
    //拍照按钮
    @IBOutlet weak var cameraButton: UIButton!
    
    //选择照片按钮
    @IBOutlet weak var galleryButton: UIButton!
    
    //选择照片并裁剪按钮
    @IBOutlet weak var cropButton: UIButton!
    
    //显示照片的imageView
    @IBOutlet weak var imageView: UIImageView!
    
    let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //初始化图片控制器
        let imagePicker = UIImagePickerController()
        
        //判断并决定"拍照"按钮是否可用
        cameraButton.isEnabled = UIImagePickerController.isSourceTypeAvailable(.camera)
        
        //“拍照”按钮点击
        cameraButton.rx.tap
            .bind { [weak self] _ -> Void in
                imagePicker.sourceType = .camera //来源为相机
                imagePicker.allowsEditing = false //不可编辑
                //弹出控制器，显示界面
                self?.present(imagePicker, animated: true)
            }
            .disposed(by: disposeBag)
        
        //“选择照片”按钮点击
        galleryButton.rx.tap
            .bind { [weak self] _ -> Void in
                imagePicker.sourceType = .photoLibrary //来源为相册
                imagePicker.allowsEditing = false //不可编辑
                //弹出控制器，显示界面
                self?.present(imagePicker, animated: true)
            }
            .disposed(by: disposeBag)
        
        //“选择照片并裁剪”按钮点击
        cropButton.rx.tap
            .bind { [weak self] _ -> Void in
                imagePicker.sourceType = .photoLibrary //来源为相册
                imagePicker.allowsEditing = true //不可编辑
                //弹出控制器，显示界面
                self?.present(imagePicker, animated: true)
            }
            .disposed(by: disposeBag)
        
        //图片选择完毕后，将其绑定到imageView上显示
        imagePicker.rx.didFinishPickingMediaWithInfo
            .map { info in
                //根据情况选择是使用原始图片还是编辑后的图片
                if imagePicker.allowsEditing {
                    return info[UIImagePickerControllerEditedImage] as! UIImage
                } else {
                    return info[UIImagePickerControllerOriginalImage] as! UIImage
                }
            }
            .bind(to: imageView.rx.image)
            .disposed(by: disposeBag)
        
        //图片选择完毕后，退出图片控制器
        imagePicker.rx.didFinishPickingMediaWithInfo
            .subscribe(onNext: { _ in
                imagePicker.dismiss(animated: true)
            })
            .disposed(by: disposeBag)
    }
}

附：功能改进

虽然前面我们对 UIImagePickerController 进行了 Rx 扩展，但使用起来还是有些不便，比如图片选择完毕后还需要在代码中手动退出选择器。下面对它做个功能改进，让其可以自动关闭退出。

1，UIImagePickerController+RxCreate.swift

这里再一次对 UIImagePickerController 进行 Rx 扩展，增加一个创建图片选择控制器的静态方法，后面当我们使用该方法初始化 ImagePickerController 时会自动将其弹出显示，并且在选择完毕后会自动关闭。

import UIKit
import RxSwift
import RxCocoa

//取消指定视图控制器函数
func dismissViewController(_ viewController: UIViewController, animated: Bool) {
    if viewController.isBeingDismissed || viewController.isBeingPresented {
        DispatchQueue.main.async {
            dismissViewController(viewController, animated: animated)
        }
        return
    }
    
    if viewController.presentingViewController != nil {
        viewController.dismiss(animated: animated, completion: nil)
    }
}

//对UIImagePickerController进行Rx扩展
extension Reactive where Base: UIImagePickerController {
    //用于创建并自动显示图片选择控制器的静态方法
    static func createWithParent(_ parent: UIViewController?,
        animated: Bool = true,
        configureImagePicker: @escaping (UIImagePickerController) throws -> () = { x in })
        -> Observable<UIImagePickerController> {
            
            //返回可观察序列
            return Observable.create { [weak parent] observer in
                
                //初始化一个图片选择控制器
                let imagePicker = UIImagePickerController()
                
                //不管图片选择完毕还是取消选择，都会发出.completed事件
                let dismissDisposable = Observable.merge(
                        imagePicker.rx.didFinishPickingMediaWithInfo.map{_ in ()},
                        imagePicker.rx.didCancel
                    )
                    .subscribe(onNext: {  _ in
                        observer.on(.completed)
                    })
                
                //设置图片选择控制器初始参数，参数不正确则发出.error事件
                do {
                    try configureImagePicker(imagePicker)
                }
                catch let error {
                    observer.on(.error(error))
                    return Disposables.create()
                }
                
                //判断parent是否存在，不存在则发出.completed事件
                guard let parent = parent else {
                    observer.on(.completed)
                    return Disposables.create()
                }
                
                //弹出控制器，显示界面
                parent.present(imagePicker, animated: animated, completion: nil)
                //发出.next事件（携带的是控制器对象）
                observer.on(.next(imagePicker))
                
                //销毁时自动退出图片控制器
                return Disposables.create(dismissDisposable, Disposables.create {
                    dismissViewController(imagePicker, animated: animated)
                })
            }
    }
}

2，ViewController.swift

主视图控制器代码如下，可以看到我们现在不需要去关心图片选择界面如何关闭了。

import UIKit
import RxSwift
import RxCocoa

class ViewController: UIViewController {
    
    //拍照按钮
    @IBOutlet weak var cameraButton: UIButton!
    
    //选择照片按钮
    @IBOutlet weak var galleryButton: UIButton!
    
    //选择照片并裁剪按钮
    @IBOutlet weak var cropButton: UIButton!
    
    //显示照片的imageView
    @IBOutlet weak var imageView: UIImageView!
    
    let disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //判断并决定"拍照"按钮是否可用
        cameraButton.isEnabled = UIImagePickerController.isSourceTypeAvailable(.camera)
        
        //“拍照”按钮点击
        cameraButton.rx.tap
            .flatMapLatest { [weak self] _ in
                return UIImagePickerController.rx.createWithParent(self) { picker in
                    picker.sourceType = .camera
                    picker.allowsEditing = false
                    }
                    .flatMap { $0.rx.didFinishPickingMediaWithInfo }
            }
            .map { info in
                return info[UIImagePickerControllerOriginalImage] as? UIImage
            }
            .bind(to: imageView.rx.image)
            .disposed(by: disposeBag)
        
        //“选择照片”按钮点击
        galleryButton.rx.tap
            .flatMapLatest { [weak self] _ in
                return UIImagePickerController.rx.createWithParent(self) { picker in
                    picker.sourceType = .photoLibrary
                    picker.allowsEditing = false
                    }
                    .flatMap { $0.rx.didFinishPickingMediaWithInfo }
            }
            .map { info in
                return info[UIImagePickerControllerOriginalImage] as? UIImage
            }
            .bind(to: imageView.rx.image)
            .disposed(by: disposeBag)
        
        //“选择照片并裁剪”按钮点击
        cropButton.rx.tap
            .flatMapLatest { [weak self] _ in
                return UIImagePickerController.rx.createWithParent(self) { picker in
                    picker.sourceType = .photoLibrary
                    picker.allowsEditing = true
                    }
                    .flatMap { $0.rx.didFinishPickingMediaWithInfo }
            }
            .map { info in
                return info[UIImagePickerControllerEditedImage] as? UIImage
            }
            .bind(to: imageView.rx.image)
            .disposed(by: disposeBag)
    }
}

Swift - RxSwift的使用详解59（DelegateProxy样例2：图片选择功能 ）