c# - CommandParameter 如何在 MVVM 中工作？

Question

我想在我的类 CommandProvider 中实现 CommandParameter，它用于命令(按钮等)并继承自 ICommand，但我不明白如何实现它。示例:

XAML

<TreeViewItem Header="Playlist" ItemsSource="{Binding ItemSourceTree}">
  <i:Interaction.Triggers>
    <i:EventTrigger EventName="MouseDoubleClick">
      <i:InvokeCommandAction Command="{Binding Path=NewPlaylist}"
                             CommandParameter="{Binding Path=NamePlaylist}" />
    </i:EventTrigger>
  </i:Interaction.Triggers>
<TreeViewItem.ItemTemplate>
   <DataTemplate DataType="{x:Type local:PlaylistDB}">
      <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding Path=NamePlaylist}">
        </TextBlock>
      </StackPanel>
    </DataTemplate>
  </TreeViewItem.ItemTemplate>
</TreeViewItem>

控制台显示，找不到 NamePlaylist。

并将函数链接到 Binding NewPlaylist:

public ICommand NewPlaylist { get { return new CommandProvider((obj) => DoubleClickTest(obj)); } }

函数

public void DoubleClickTest(object obj)
        {
            var tmp = obj as string;
            Console.WriteLine(tmp);
        }

所以我需要修改我的类 CommandProvider 以正确获取参数？我该怎么做？

CommandProvider

public class CommandProvider : ICommand
{
#region Constructors       

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

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

#endregion

#region ICommand Members

public event EventHandler CanExecuteChanged;

public bool CanExecute(object parameter)
{
    return _canExecute != null ? _canExecute(parameter) : true;
}

public void Execute(object parameter)
{
    if (_execute != null)
        _execute(parameter);
}

public void OnCanExecuteChanged()
{
    CanExecuteChanged(this, EventArgs.Empty);
}

#endregion

private readonly Action<object> _execute = null;
private readonly Predicate<object> _canExecute = null;
}

播放列表数据库

public class PlaylistDB
    {
        public string NamePlaylist { get; set; }
    }

我想在我的函数 DoubleClickTest() 中检索 NamePlaylist，并且我想在 CommandParameter 中传递它。我该怎么做？

Answer 1

使用下面的类接受 commandparameters 使用 ICommand,

public class DelegateCommand: ICommand
{
    #region Constructors       

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

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

    #endregion

    #region ICommand Members

    public event EventHandler CanExecuteChanged;

    public bool CanExecute(object parameter)
    {
        return _canExecute != null ? _canExecute(parameter) : true;
    }

    public void Execute(object parameter)
    {
        if (_execute != null)
            _execute(parameter);
    }

    public void OnCanExecuteChanged()
    {
        CanExecuteChanged(this, EventArgs.Empty);
    }

    #endregion

    private readonly Action<object> _execute = null;
    private readonly Predicate<object> _canExecute = null;
}

用法:

public ICommand CloseCommand
    {
        get
        {
            return new DelegateCommand((obj)=>CloseMethod(obj));
        }
    }

obj为上例中传入的命令参数。