Swift 错误“UIButton.currentTitle 必须仅在主线程中使用" [英] Swift Error "UIButton.currentTitle must be used from main thread only"

问题描述

我刚刚从以下链接关注了这个你管教程:

网址:

导入 UIKit导入媒体播放器类 GenreButtonScreen: UIViewController {var musicPlayer = MPMusicPlayerController.applicationMusicPlayer@IBAction funcgenreButtonTapped(_ sender: UIButton) {MPMediaLibrary.requestAuthorization {(状态)在如果状态 == .authorized {self.playGenre(流派:sender.currentTitle！)}}}@IBAction func stopButtonTapped(_ sender: UIButton) {音乐播放器.stop()}@IBAction func nextButtonTapped(_ sender: UIButton) {音乐播放器.skipToNextItem()}功能播放流派(流派:字符串){音乐播放器.stop()让查询 = MPMediaQuery()让谓词 = MPMediaPropertyPredicate(值:流派，forProperty:MPMediaItemPropertyGenre)查询 .addFilterPredicate(谓词)musicPlayer.setQueue(with: query)musicPlayer.shuffleMode = .songs音乐播放器.play()}}

解决方案

MPMediaLibrary.requestAuthorization 是异步调用，布局组件只能在主线程中修改.你应该这样使用:

 MPMediaLibrary.requestAuthorization { (status) in如果状态 == .authorized {DispatchQueue.main.async {self.playGenre(流派: sender.currentTitle ?? String())}}}

I just followed this you tube tutorial from the following link:

URL: https://www.youtube.com/watch?v=aiXvvL1wNUc

I cam across an error saying "UIButton.currentTitle must be used from main thread only"

Not really sure how to fix this as I am new to making apps, can anyone help me?

Greatly appreciated and thanks in advance!

import UIKit
import MediaPlayer

class GenreButtonScreen: UIViewController {
    var musicPlayer = MPMusicPlayerController.applicationMusicPlayer

    @IBAction func genreButtonTapped(_ sender: UIButton) {
        MPMediaLibrary.requestAuthorization { (status) in
            if status == .authorized {
                self.playGenre(genre: sender.currentTitle!)
            }
        }
    }

    @IBAction func stopButtonTapped(_ sender: UIButton) {
        musicPlayer.stop()
    }

    @IBAction func nextButtonTapped(_ sender: UIButton) {
        musicPlayer.skipToNextItem()
    }

    func playGenre(genre:String) {
        musicPlayer.stop()

        let query = MPMediaQuery()
        let predicate = MPMediaPropertyPredicate(value: genre, forProperty: MPMediaItemPropertyGenre)

        query .addFilterPredicate(predicate)

        musicPlayer.setQueue(with: query)
        musicPlayer.shuffleMode = .songs 
        musicPlayer.play()
    }
}

解决方案

The MPMediaLibrary.requestAuthorization is an async call, and layout components only can be modified in the Main Thread. You should use this way:

 MPMediaLibrary.requestAuthorization { (status) in
    if status == .authorized {
        DispatchQueue.main.async { 
           self.playGenre(genre: sender.currentTitle ?? String()) 
        }
    }
}

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