Why is this Swift web scraper not working? - swift

Question

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!!

Answer 1

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()
}
}