Question

我正在通过iOS Apple Developer Tutorial工作，但由于我的计算机版本的Swift是1.2而Xcode是6.4而不是Swift 3.0，因此我遇到了一些问题。我已经能够根据需要同时降级代码，但是在＃34; guard let＆＃34;中出现了错误，这是在下面的Swift 2.0中引入的：

// The info dictionary may contain multiple representations of the image. 
// You want to use the original.

guard let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage else {
    fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
}

我将其转换为以下内容：

if let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage {
     return selectedImage
} else {
     fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
}

//Set photoImageView to display the image.
photoImageView.image = selectedImage

但是我收到了以下错误：＆＃34;使用未解决的已识别的＆＃39; selectedImage＆＃39;＆＃34;

非常感谢任何帮助！

编辑：以下完整代码

import UIKit

class ViewController: UIViewController, UITextFieldDelegate,
UIImagePickerControllerDelegate, UINavigationControllerDelegate {

//MARK: Properties
@IBOutlet weak var nameTextField: UITextField!
@IBOutlet weak var mealNameLabel: UILabel!
@IBOutlet weak var photoImageView: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()

    //Handle the text field's user input through the delegate callbacks
    nameTextField.delegate = self
}


//MARK: UITextFieldDelegate
func textFieldShouldReturn(textField: UITextField) -> Bool {
    //Hide the keyboard
    textField.resignFirstResponder()
    return true
}
func textFieldDidEndEditing(textField: UITextField) {
    //Set the lablel name as what the used typed
    mealNameLabel.text = textField.text
}

//MARK: UIImagePickerControllerDelegate
func imagePickerControllerDidCancel(picker: UIImagePickerController) {
    //Dismiss the picker if the user canceled
    dismissViewControllerAnimated(true, completion:nil)
}
func imagePickerController(picker: UIImagePickerController,
    didFinishPickingMediaWithInfo info: [String : Any]) {
        //The info dictionary may contain multiple representations of the image. You want to use the original.
        if let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage {
            //Set photoImageView to display the image
            photoImageView.image = selectedImage
        } else {
            fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
        }

        //Set photoImageView to display the image
        //photoImageView.image = selectedImage

        //Dismiss the picker
        dismissViewControllerAnimated(true, completion: nil)
}


//MARK: Actions
@IBAction func selectImageFromPhotoLibrary(sender: UITapGestureRecognizer) {
    //Hide the keyboard
    nameTextField.resignFirstResponder()

    //UIImagePickerController is a view controller that lets a user pick media from their photo library.
    let imagePickerController = UIImagePickerController()


    //Only allow photos to be picked, not taken.
    imagePickerController.sourceType = .PhotoLibrary

    //Make sure ViewController is notified when the user picks and image.
    imagePickerController.delegate = self
    presentViewController(imagePickerController, animated: true, completion: nil)

}
@IBAction func setDefaultLabelText(_: UIButton) {
    mealNameLabel.text = "Default Text"
}
}

Answer 1

这是因为您的变量selectedImage仅在if let范围内定义

您必须使用此代码

if let selectedImage = info[UIImagePickerControllerOriginalImage] as? UIImage{
     //Set photoImageView to display the image.
     photoImageView.image = selectedImage
     return selectedImage
} else {
     fatalError("Expected a dictionary containing an image, but was provided the following: \(info)")
}

我希望这会有所帮助

Answer 2

int i = sex ? 1 : 0;可选绑定语句创建一个仅存在于以下大括号内的新变量：

if let

guard let创建一个新的变量，该变量在当前作用域结束后从代码中存在：

if let foo = optionalFoo {
  //foo is only defined here
}

//foo has gone out of scope.

由于Swift 1没有保护声明，您需要将func bar(optionalFoo: FooThing) { guard let foo = optionalFoo else {return} //foo exists from here until the end of the //current scope (the end of the func) }之后的代码移到guard let的大括号内

看起来@ReinierMelian用他的回答打败了我。请参阅他在Swift 1.x中的正确代码形式的答案。

请注意，Swift 1.0已经过时了，而且你在使用它时会对自己造成伤害。您应该升级到Xcode 8.3和Swift 3.1。从Swift 1到Swift 2的变化很大，从Swift 2到Swift 3的变化是大。 Swift 1代码无法在Xcode 8中编译，您可能无法通过自动转换运行它。（Xcode 8将通过自动转换为Swift 3来运行Swift 2.x，但我不确定它是否会将Swift 1转换为Swift 3。

如果Let vs Guard让我们在Swift 1.2中使用UIImage

2 个答案: