Question

我一直在尝试在Swift中开发全功能音乐应用程序。我试图查看用swift编写的可用开源音乐应用程序。我发现了一个有用的音乐应用程序（ESTMusicPlayer）但是这个应用程序是用目标C

我使用Swift Interpolablity和Mix-Match功能几乎用MusicListViewContorller.swift取代了MusicListViewContorller.h和MusicListViewContorller.m文件的Objective-C版本。

我已经转换了Objective-C版本：

 - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if (_delegate && [_delegate respondsToSelector:@selector(playMusicWithSpecialIndex:)]) {
        [_delegate playMusicWithSpecialIndex:indexPath.row];
    } else {
        MusicViewController *musicVC = [MusicViewController sharedInstance];
        musicVC.musicTitle = self.navigationItem.title;
        musicVC.musicEntities = _musicEntities;
        musicVC.specialIndex = indexPath.row;
        musicVC.delegate = self;
        [self presentToMusicViewWithMusicVC:musicVC];
    }
    [self updatePlaybackIndicatorWithIndexPath:indexPath];
    [tableView deselectRowAtIndexPath:indexPath animated:YES];
}

要

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    delegate?.playMusicSpecial(indexPath.row)

    self.updatePlayBackIndicatorWithIndexPath(indexPath)
    tableView.deselectRowAtIndexPath(indexPath, animated: true)
}

什么是等效的Swift中以下代码的代码片段？

if (_delegate && [_delegate respondsToSelector:@selector(playMusicWithSpecialIndex:)]) {
    [_delegate playMusicWithSpecialIndex:indexPath.row];
}

什么是swift中respondToSelector:的替代代码？

Answer 1

我们可以通过Optional chaining检查委托实现特定方法。要执行可选链接方法，应该是可选类型。

您可以在协议中定义可选方法。

@objc protocol MyProtocol:class
{
    func requiredMethod()
    optional func playMusicWithSpecialIndex(index : int)
}

请在协议中查看Optional Method declaration的此链接。

试试这段代码。这可能会对你有帮助。

 func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

if _delegate.playMusicWithSpecialIndex?(indexPath.row) {

    //Method Exist

}else{

    var musicVC: MusicViewController = MusicViewController.sharedInstance()
    musicVC.musicTitle = self.navigationItem.title
    musicVC.musicEntities = musicEntities
    musicVC.specialIndex = indexPath.row
    musicVC.delegate = self
    self.presentToMusicViewWithMusicVC(musicVC)
}
    self.updatePlaybackIndicatorWithIndexPath(indexPath)
    tableView.deselectRowAtIndexPath(indexPath, animated: true)

}

didSelectRowAtIndexPath不起作用

1 个答案: