Swift 4 func prepare（for segue：UIStoryboardSegue，sender：Any？）不使用indexPath.row更新Int变量 [英] Swift 4 func prepare(for segue: UIStoryboardSegue, sender: Any?) not updating Int variable with indexPath.row

问题描述

全部！我正在尝试将上一课与音频播放器结合起来，但是遇到了一个问题。我有一个变量 activeSong ，它等于 indexPath.row 使用方法 func tableView（ _ tableView：UITableView，didSelectRowAt indexPath：IndexPath）。发生的是，当我打印 indexPath.row 时，其值与activeSong不同。知道为什么会这样。我认为func prepare（用于segue：UIStoryboardSegue，发件人：任何？）方法做错了。

all! I'm trying to combine previous lessons with the Audio Player, but I'm running into an issue. I have a variable activeSong which is equal to indexPath.row using the method func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath). What happens is that when I print  indexPath.row its value is different form activeSong. Any idea why this might be happening. I think I'm doing something wrong with the func prepare(for segue: UIStoryboardSegue, sender: Any?) method. Thanks!!

/
//  MySongsController.swift
//  Audio Player
//
//  Created by Alex Gomez on 10/31/18.
//  Copyright © 2018 Alex Gomez. All rights reserved.
//

import UIKit

var activeSong = -1
var isPlaying = false

class MySongsController: UITableViewController {

    var songsList = [Song()]

    @IBOutlet var table: UITableView!


    override func viewDidLoad() {
        super.viewDidLoad()

        if songsList.count == 1 && songsList[0].songTitle == "" {
            songsList.remove(at: 0)
            songsList.append(Song(songTitle: "El Colibri", songArtist: "Santiago Feliu", songFormat: "MP3"))
        }

        songsList.append(Song(songTitle: "Amargas Verdades", songArtist: "Santiago Feliu", songFormat: "MP3"))
        table.reloadData()

        // print("There are \(songsList.count) songs in the list")
        // print("Active song is \(activeSong)")
    }


    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    // Number of cells
    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return songsList.count
    }

    // Cell title
    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = UITableViewCell(style: UITableViewCell.CellStyle.default, reuseIdentifier: "Cell")

        cell.textLabel?.text = "\(songsList[indexPath.row].songTitle) — \(songsList[indexPath.row].songArtist)"

        return cell
    }

    // Go to "Now Playing" view once a cell is selected
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        performSegue(withIdentifier: "toNowPlaying", sender: indexPath)
        activeSong = indexPath.row

        // print("—––––")
        // print("Index Path row is \(indexPath.row)")
        // print("Active song \(activeSong) — \(songsList[activeSong].songTitle)")

    }

    // Pass song information along to Now Playing view
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        if segue.identifier == "toNowPlaying" {
            let nowPlayingView = segue.destination as! ViewController
            nowPlayingView.playing = activeSong
        }
    }
}

推荐答案

在设置 activeSong 之前，您先调用 performSegue 。交换订单。

You call performSegue before setting activeSong. Exchange the order.

实际上，您不需要 activeSong 。无论如何，当您移交 indexPath 时，只需使用它即可：

Actually you don't need activeSong. As you hand over the indexPath anyway just use it:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "toNowPlaying" {
        let nowPlayingView = segue.destination as! ViewController
        let indexPath = sender as! IndexPath
        nowPlayingView.playing = indexPath.row
    }
}

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