Why is this Swift web scraper not working?-CodePudding

I am having trouble scraping an image HTML link with a code I found on youtube (https://www.youtube.com/watch?v=0jTyKu9DGm8&list=PLYjXqILgs9uPwYlmSrIkNj2O3dwPCcoBK&index=2). The code works perfectly fine in a playground, but there is something wrong with my implementation into an Xcode project. (More like: im not sure how to implement it into my project :) )

When I ran this code on a Playground it pulled the link that I needed exactly as I needed it to be outputted.

import Foundation

let url = URL(string: "https://guide.michelin.com/th/en/bangkok- 
region/bangkok/restaurant/somtum-khun-kan")

let task = URLSession.shared.dataTask(with: url!) { (data, resp, error) in
    guard let data = data else {
        print("data was nil")
        return
    }
    guard let htmlString = String(data: data, encoding: String.Encoding.utf8) else {
        print("can not cast data into string")
        return
    }

    let leftSideOfTheString = """
    image":"
    """

    let rightSideOfTheString = """
    ","@type
    """

    guard let leftRange = htmlString.range(of: leftSideOfTheString) else {
        print("can not find left range of string")
        return
    }

    guard let rightRange = htmlString.range(of: rightSideOfTheString) else {
        print("can not find right range of string")
        return
    }

    let rangeOfValue = leftRange.upperBound..<rightRange.lowerBound

    print(htmlString[rangeOfValue])
}
task.resume()

I then put the same exact code into a structure containing the code as a parameter and method, like so:

struct ImageLink {

    let url = URL(string: "https://guide.michelin.com/th/en/bangkok-region/bangkok/restaurant/somtum-khun-kan")

    func getImageLink() {
    
        let task = URLSession.shared.dataTask(with: url!) { (data, resp, error) in
            guard let data = data else {
                print("data was nil")
                return
            }
            guard let htmlString = String(data: data, encoding: String.Encoding.utf8) else {
                print("can not cast data into string")
                return
            }
        
            let leftSideOfTheString = """
                image":"
                """
        
            let rightSideOfTheString = """
                ","@type
                """
        
            guard let leftRange = htmlString.range(of: leftSideOfTheString) else {
                print("can not find left range of string")
                return
            }
        
            guard let rightRange = htmlString.range(of: rightSideOfTheString) else {
                print("can not find right range of string")
                return
            }
        
            let rangeOfValue = leftRange.upperBound..<rightRange.lowerBound
        
            print(htmlString[rangeOfValue])
        }
        task.resume()
    }
}

Finally, to check if the code would give me the right link, I made an instance in a View and made a button printing the getImageLink() function like bellow. You'll see in commented out code that I tried displaying the image both by hard coding its link and by inserting the function call. The former worked as expected, the latter did not work.

import SwiftUI

struct WebPictures: View {

    var imageLink = ImageLink()

    var body: some View {
        VStack {
            //AsyncImage(url: URL(string: "\(imageLink.getImageLink())"))
            //AsyncImage(url: URL(string: "https://axwwgrkdco.cloudimg.io/v7/__gmpics__/c8735576e7d24c09b45a4f5d56f739ba?width=1000"))
            Button {
                print(imageLink.getImageLink())
            } label: {
                Text("Print Html")
            }
        }
    }
}

When I click the button to print the link I get the following message:

()
2022-05-16 17:21:30.030264 0800 MichelinRestaurants[35477:925525] [boringssl] 
boringssl_metrics_log_metric_block_invoke(153) Failed to log metrics
https://axwwgrkdco.cloudimg.io/v7/__gmpics__/c8735576e7d24c09b45a4f5d56f739ba?width=1000

And if I click the button for a second time only this gets printed:

()
https://axwwgrkdco.cloudimg.io/v7/__gmpics__/c8735576e7d24c09b45a4f5d56f739ba?width=1000

If anybody knows how to help me out here that would be much appreciated!!

CodePudding user response：

This fails because you do not wait until your func has pulled the link. You are in an async context here. One possible solution:

//Make a class in instead of a struct and inherit from ObservableObject
class ImageLink: ObservableObject {

    let url = URL(string: "https://guide.michelin.com/th/en/bangkok-region/bangkok/restaurant/somtum-khun-kan")
    //Create a published var for your view to get notified when the value changes
    @Published var imageUrlString: String = ""
    func getImageLink() {
    
        let task = URLSession.shared.dataTask(with: url!) { (data, resp, error) in
            guard let data = data else {
                print("data was nil")
                return
            }
            guard let htmlString = String(data: data, encoding: String.Encoding.utf8) else {
                print("can not cast data into string")
                return
            }
        
            let leftSideOfTheString = """
                image":"
                """
        
            let rightSideOfTheString = """
                ","@type
                """
        
            guard let leftRange = htmlString.range(of: leftSideOfTheString) else {
                print("can not find left range of string")
                return
            }
        
            guard let rightRange = htmlString.range(of: rightSideOfTheString) else {
                print("can not find right range of string")
                return
            }
        
            let rangeOfValue = leftRange.upperBound..<rightRange.lowerBound
        
            print(htmlString[rangeOfValue])
            //Assign the scrapped link to the var
            imageUrlString = htmlString[rangeOfValue]
        }
        task.resume()
    }
}

And the view:

struct WebPictures: View {
    //Observe changes from your imagelink class
    @StateObject var imageLink = ImageLink()

    var body: some View {
        VStack {
            AsyncImage(url: URL(string: imageLink.imageUrlString)) // assign imageurl to asyncimage
            //AsyncImage(url: URL(string: "https://axwwgrkdco.cloudimg.io/v7/__gmpics__/c8735576e7d24c09b45a4f5d56f739ba?width=1000"))
            Button {
                imageLink.getImageLink()
            } label: {
                Text("Print Html")
            }
        }
    }
}

Update:

In order to get the link when the view appears call it this way:

        VStack {
            AsyncImage(url: URL(string: imageLink.imageUrlString)) 
        }
         .onAppear{
             if imageLink.imageUrlString.isEmpty{
                 imageLink.getImageLink()
             }
          }