将 completionSelector 和 completionTarget 与 UIImageWriteToSavedPhotosAlbum 一起使用

Question

我正在想办法让我的 iOS 应用程序将屏幕截图保存到相机胶卷，然后弹出一个警报，告诉用户屏幕截图已成功保存。

我能想到的唯一方法是使用某种形式的 if/else 循环（正如您将在下面的伪代码 cmets 中看到的那样），但我想不出任何语法可以使用 @来自 UIKit 的 987654321@ 函数。我在 Apple 的开发站点上遇到过使用 completionSelector 和 completionTarget 的建议，但我真的不明白如何使用它们，或者我的代码中的 completionSelector 和 completionTarget 应该使用什么特定的用语。我对 Swift 比较陌生。

有人能解释一下它们是如何工作的，以及如何在我的代码中找到使用它们的语法吗？

func screenshotMethod()
{
    UIGraphicsBeginImageContextWithOptions(HighchartsView.scrollView.contentSize, false, 0);
    view.layer.renderInContext(UIGraphicsGetCurrentContext())
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
    //if saved to Camera Roll
    //            {
    //              confirmScreenshot()
    //            }
    //        
    //else 
    //        {
    //            exit code/stop 
    //        }


}


func confirmScreenshot()
{
    let alertController = UIAlertController(title: "Success", message: "This chart has been successfully saved to your Camera Roll.", preferredStyle: .Alert)
    let defaultAction = UIAlertAction(title: "OK", style: .Default, handler: nil)
    alertController.addAction(defaultAction)

    presentViewController(alertController, animated: true, completion: nil)
}

Answer 1

import UIKit

class ViewController: UIViewController {

   @IBAction func buttonPressed(sender: AnyObject) {
      presentImagePickerController()
   }

}

extension ViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {

   func presentImagePickerController() {
      let imagePickerController = UIImagePickerController()
      imagePickerController.delegate = self
      imagePickerController.sourceType = .PhotoLibrary
      imagePickerController.allowsEditing = false

      presentViewController(imagePickerController, animated: true, completion: nil)
   }

   func imagePickerController(picker: UIImagePickerController, didFinishPickingImage image: UIImage, editingInfo: [String : AnyObject]?) {
      UIImageWriteToSavedPhotosAlbum(image, self, "image:didFinishSavingWithError:contextInfo:", nil)
   }

   func imagePickerControllerDidCancel(picker: UIImagePickerController) {
      self.dismissViewControllerAnimated(true, completion: nil)
   }

   func image(image: UIImage, didFinishSavingWithError error: NSError?, contextInfo:UnsafePointer<Void>) {
      guard error == nil else {
         //Error saving image
         return
      }
      //Image saved successfully
   }

}

Answer 2

这是一个工作示例，用于在 SWIFT 3.0 中工作的相机胶卷中保存当前视图的屏幕截图

 @IBAction func saveScreenshot(_ sender: Any) {

    //Create the UIImage
    UIGraphicsBeginImageContextWithOptions(editorView.frame.size, false, UIScreen.main.scale)

    //  UIGraphicsBeginImageContext(myTextView.frame.size)
    editorView.layer.render(in: UIGraphicsGetCurrentContext()!)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    UIImageWriteToSavedPhotosAlbum(image!, self, #selector(TextEditorViewController.image(_:didFinishSavingWithError:contextInfo:)), nil)

}

func image(_ image: UIImage, didFinishSavingWithError error: NSError?, contextInfo: UnsafeRawPointer) {
if let error = error {
    // we got back an error!
    let ac = UIAlertController(title: "Save error", message: error.localizedDescription, preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "OK", style: .default))
    present(ac, animated: true)
} else {
    let ac = UIAlertController(title: "Saved!", message: "Your image has been saved to your photos.", preferredStyle: .alert)
    ac.addAction(UIAlertAction(title: "OK", style: .default))
    present(ac, animated: true)
}

}

Answer 3

@Dare 的错误检查解决方案对我不起作用（Swift 2.0）。

这个小小的修改确实奏效了：

func image(image: UIImage, didFinishSavingWithError: NSError?, contextInfo:UnsafePointer<Void>)       {
        if didFinishSavingWithError != nil
        {
            Helper.showNotifierInfo(DefaultTextFailed)
        }
        else
        {
            Helper.showNotifierInfo(DefaultTextSaved)
        }
    }

Answer 4

swift 2.2 中的另一个例子

这个例子的主要区别在于具有回调函数的类必须从 NSObject 扩展，（@objc 也可以工作）

func writeImage(){
    let responder = WriteImageToFileResponder()
    responder.addCompletion{ print("completed") }

    let image = UIImage(color: .redColor(), size: CGSize(width: 100, height: 100))!
    UIImageWriteToSavedPhotosAlbum(image, responder, #selector(WriteImageToFileResponder.image(_:didFinishSavingWithError:contextInfo:)), nil)
}

class WriteImageToFileResponder: NSObject {
    var completion: (() -> Void)?

    func image(image: UIImage, didFinishSavingWithError error: NSError?, contextInfo: UnsafeMutablePointer<Void>) {
        print(error)
        completion?()

    }

    func addCompletion(completion: (() -> Void)? ) {
        self.completion = completion
    }
}

Answer 5

我从@David Rees 帖子更新了 Swift 5 版本

import Foundation
class WriteImageToFileResponder: NSObject {
    typealias WriteImageToFileResponderCompletion = ((UIImage?, Error?) -> Void)?
    var completion: WriteImageToFileResponderCompletion = nil
    
    override init() {
        super.init()
    }
    
    @objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) {
        if (completion != nil) {
            error == nil ? completion?(image, error) : completion?(nil, error)
            completion = nil
        }
    }
    func addCompletion(completion:WriteImageToFileResponderCompletion) {
        self.completion = completion
    }
}

使用

let responder = WriteImageToFileResponder()
responder.addCompletion { (image, error) in
// completion block
}
// pass your image that you want to write 
let previewImage = UIImage(named:"sample")
UIImageWriteToSavedPhotosAlbum(previewImage, responder, #selector(WriteImageToFileResponder.image(_:didFinishSavingWithError:contextInfo:)), nil)