I want to resolve the error displayed in Xcode.

I looked it up online, but I couldn't find a solution.

In such cases, it would be better to look it up online and write down what information you got and what you tried.Even if you search the error message Cannot use instance member 'bottunPath' with in property initializer; property initializers run before 'self' is available, you have found many articles that apply to you.Of course, there are many in Japanese.

So, don't worry too much about the latter half of the error message because it's an excuse from the Swift compiler creator who said why you're making such an error.

Cannot use instance member 'bottunPath' with in property initializer

Your code declares two instance properties bottunPath and bottunPlayer, of which bottunPlayer is the initializer (property initializer), AVAudioPlayer (contentOf:bottunPath, fileTypePhint:code), , in the instance.

Another instance member (instance member --instance property or instance method) cannot be used in the initialization expression when declaring instance properties

This is Swift's rule as a programming language, so you have to follow it.

Specifically, for your code, bottunPlayer does not have a meaningful value until the button is pressed, so it should be optional.

This is what it looks like if you correct any other incorrect code writing.

import UIKit
import AVFoundation

classViewController:UIViewController {
  
    override func viewDidLoad(){
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
    }
    
    //Usually use `url(forResource:withExtension:)` to retrieve URLs to in-app resources
    // Intentionally use forced unwrap (`!`) to indicate that if you make a mistake, it will crash and let you know.
    let buttonUrl = Bundle.main.url (forResource: "BUTTON", withExtension: "mp3")!
    // If the appropriate initial value cannot be set, leave it as an optional type, and the initial value automatically nil
    var buttonPlayer —AVAudioPlayer?
    
    // Swift does not use names that start with capital letters other than type names
    @ IBAction func buttonTapped(_sender:Any){
        do{
            buttonPlayer=try AVAudioPlayer(contentsOf:buttonUrl,fileTypeHint:nil)
            
            // Since `buttonPlayer` is an optional type, use Optional Chaining
            buttonPlayer?play()
        } catch{
            // If an error is caught, it is difficult to debug without providing information about the error.
            print("Error in BUTTON:\(error)")
        }
    }
}

Rewriting the name of an action method that you've connected to (most introductions don't say much about how to fix mistakes), but you'd better take the plunge as it's something you'll eventually have to learn.

Instead of copying it completely, try it as a reference.

By the way, the second warning appears to be caused by the first error that some of the sentences are treated as missing (when there is no sentence in the do-catch that uses try).Try to clear up the error first.