如何将CommandParameter与RelayCommand一起使用？

我仍在学习MVVM和WPF的知识，此刻我正在尝试使用MVVM创建Mediaplayer。经过大量的搜索后，我决定使用CommanParameter是避免代码隐藏的最好方法。我认为代码和XAML看起来很好，但没有魔术 - AKA什么也没有发生。如何将CommandParameter与RelayCommand一起使用？

有没有什么好的灵魂在那里谁会介意看看我的代码，并给我一些建议？一如既往，我真正珍惜你的答案。一旦物业VideoToPlay已设置请忽略我在RelayCommands复数，当时天色已晚:)

XAML

<MediaElement Name="MediaElement" 
    Source="{Binding VideoToPlay}" 
    Width="400" Height="180" Stretch="Fill" 
    LoadedBehavior="Manual" UnloadedBehavior="Manual"/> 
<Slider Name="timelineSlider" Margin="5" Width="250" 
    HorizontalAlignment="Center"/> 
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center"> 
<Button 
    Command="{Binding PlayMediaCommand}" 
    CommandParameter="{Binding ElementName=MediaElement, Mode=OneWay}">&lt;&lt;</Button>

C＃

class MediaPlayerViewModel: INotifyPropertyChanged 
{ 
    private MediaElement MyMediaElement; 

    private Uri _videoToPlay; 

    public Uri VideoToPlay 
    { 
     get { return _videoToPlay; } 
     set 
     { 
      _videoToPlay = value; 
      OnPropertyChanged("VideoToPlay"); 
     } 
    } 

    void SetMedia() 
    { 
     OpenFileDialog dlg = new OpenFileDialog(); 
     dlg.InitialDirectory = "c:\\"; 
     dlg.Filter = "Media files (*.wmv)|*.wmv|All Files (*.*)|*.*"; 
     dlg.RestoreDirectory = true; 

     if (dlg.ShowDialog() == true) 
     { 
      VideoToPlay = new Uri(dlg.FileName); 

     } 
    } 

    RelayCommands _openFileDialogCommand; 
    public ICommand OpenFileDialogCommand 
    { 
     get 
     { 
      if (_openFileDialogCommand == null) 
      { 
       _openFileDialogCommand = new RelayCommands(p => SetMedia(), 
        p => true); 
      } 
      return _openFileDialogCommand; 
     } 
    } 

    RelayCommands _playMediaCommand; 
    public ICommand PlayMediaCommand 
    { 
     get 
     { 
      if (_playMediaCommand == null) 
      { 
       _playMediaCommand = new RelayCommands(p => PlayMedia(p), 
        p => true); 
      } 
      return _playMediaCommand; 
     } 
    } 

    void PlayMedia(object param) 
    { 
     var paramMediaElement = (MediaElement)param; 
     MyMediaElement = paramMediaElement; 
     MyMediaElement.Source = VideoToPlay; 
     MyMediaElement.Play(); 
    } 



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

    public event PropertyChangedEventHandler PropertyChanged; 




class RelayCommands: ICommand 
{ 
    private readonly Predicate<object> _canExecute; 
    private readonly Action<object> _execute; 

    public event EventHandler CanExecuteChanged; 

    public RelayCommands(Action<object> execute) 
     : this(execute, null) 
    {} 

    public RelayCommands(Action<object> execute, 
        Predicate<object> canExecute) 
    { 
     _execute = execute; 
     _canExecute = canExecute; 
    } 

    public bool CanExecute(object parameter) 
    { 

     if (_canExecute == null) 
     { 
      return true; 
     } 

     return _canExecute(parameter); 
    } 

    public void Execute(object parameter) 
    { 
     _execute(parameter); 
    } 

    public void RaiseCanExecuteChanged() 
    { 
     if (CanExecuteChanged != null) 
     { 
      CanExecuteChanged(this, EventArgs.Empty); 
     } 
    } 

}

来源

2011-12-06 Iris Classon

我假设您已经在视图上设置了数据上下文？ – kenny

是的，我做到了:)它被设置为窗口 –

你的示例代码工作正常。你确定你在设置吗？您的XAML代码段不包含任何使用此属性的OpenFileDialogCommand：

<Button Content="Select File" Command="{Binding OpenFileDialogCommand}" />

来源

2011-12-07 00:45:20

我在Top菜单中使用了这个命令，我忘记了在这里的代码中显示:)但它在那里。我仍然无法播放按钮播放视频。 –

哦亲爱的，我刚刚意识到我做错了什么....该命令是在错误的按钮。它在<<按钮上。有人请给我一个虚拟耳光。 –

SLAP :) SLAP :) – SvenG

如何将CommandParameter与RelayCommand一起使用？

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