Question

所以我正在尝试创建自己的音乐播放器。我有一个Listview正确更新当前播放列表。当我想要一个网格显示当前正在播放的歌曲时，我的问题就开始了。绑定到这些字符串时，它们都返回Null。

来自班级：

public class Song : INotifyPropertyChanged
{
    public string Title { get; set; }
    public string Path { get; set; }
    public string Artist { get; set; }
    public int Time { get; set; }
    public string Album { get; set; }
    //public ImageBrush Portrait { get; set; }
    public event PropertyChangedEventHandler PropertyChanged;


    public Song(string title, string path, string artist, int time, string album)//, ImageBrush portrait)
    {
        this.Path = path;
        this.Title = title;
        this.Artist = artist;
        this.Time = time;
        this.Album = album;
        //this.Portrait = portrait;
    }

    public string SongCurrentPlaying
    {
        get { return Title; }
        set
        {
            Title = value;
            OnPropertyChanged("SongCurrentPlaying");
        }
    }

    protected void OnPropertyChanged(string name)
    {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(Title));
        }
    }

来自XAML：

        <Grid HorizontalAlignment="Left" Height="143" VerticalAlignment="Top" Width="276">
            <Image HorizontalAlignment="Left" Height="124" Margin="10,10,0,0" VerticalAlignment="Top" Width="134" Stretch="Fill"/>
            <TextBlock HorizontalAlignment="Left" Margin="144,100,0,0" TextWrapping="Wrap" Text="{Binding Songs.Title}" VerticalAlignment="Top" Height="25" Width="122"/>
            <TextBlock HorizontalAlignment="Left" Margin="144,40,0,0" TextWrapping="Wrap" Text="{Binding SongCurrentPlaying.Title, PresentationTraceSources.TraceLevel=High}" VerticalAlignment="Top" Height="25" Width="122"/>
            <TextBlock HorizontalAlignment="Left" Margin="144,70,0,0" TextWrapping="Wrap" Text="{Binding Song.Title}" VerticalAlignment="Top" Height="25" Width="122"/>
            <TextBlock HorizontalAlignment="Left" Margin="144,10,0,0" TextWrapping="Wrap" Text="{Binding Songs.Title}" VerticalAlignment="Top" Height="25" Width="122"/>
        </Grid>

正如您所看到的，我一直在尝试使用不同的绑定来从Title获取值作为示例，但没有一个成功。

Answer 1

你的班级结构没有多大意义。您有一个Song课程，其中包含Song个信息。但是，该课程也持有SongCurrentPlaying。现在，如果您意味着与SongCurentPlaying在同一个类上Song，那么我会将您的问题缩小到如何执行XAML绑定。我假设您的控件的DataContext尚未设置为Song的实例。 e.g。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        var someSong = new Song(...);
        this.DataContext = someSong;
        InitializeComponent();
    }
}

一旦设置为DataContext，您就可以绑定到班级＆＃39;属性直接（例如{Binding Title}）。

Answer 2

您的歌曲课程不需要实施INotifyPropertyChanged。您应该将您的歌曲视为模特。相反，您应该为您的音乐播放器制作一个视图模型，该视图模型将保存您视图的所有信息，例如CurrentSongPlaying。

我会制作一个看起来像这样的viewmodel

internal class SongPlayerViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;

private Song _songPlaying;

public Song SongPlaying
{
  get { return _songPlaying; }
  set { 
    _songPlaying = value;
    OnPropertyChanged("SongPlaying");
  }
}



protected void OnPropertyChanged(string name)
{
  var handler = PropertyChanged;
  if (handler != null)
  {
    handler(this, new PropertyChangedEventArgs(name));
  }
}

}

然后确保在视图中将datacontext设置为此实例，并在xaml内部使用这样的代码绑定标题。

datacontext setup

private readonly SongPlayerViewModel _viewModel = new SongPlayerViewModel();

public MainWindow() 
{
   InitializeComponent();
   DataContext = _viewModel;
}

当前歌曲播放的xaml绑定示例

<TextBlock text="{Binding SongPlaying.Title}"/>

如果您在没有播放歌曲时需要某些内容，请查看Fallbackvalue

麻烦将类绑定到网格，第二位

2 个答案: