CODEWITHSUNDEEP
c#wpfmvvm
Raphael Teyssandier
Raphael Teyssandier

Reputation: 1777

How CommandParameter works in MVVM?

I want to implement the CommandParameter in my class CommandProvider, which use for a command (Button, etc.) and inherit from ICommand, but I didn't understand how to implement that. Example:

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>

The console says, NamePlaylist doesn't found.

And link a function to the Binding NewPlaylist:

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

Function

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

So I need to modify my class CommandProvider to take parameter right? How I can do that?

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;
}

PlaylistDB

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

I want to retrieve the NamePlaylist in my function DoubleClickTest(), and I want to pass it in CommandParameter. How can I do that?

Upvotes: 2

Views: 2137

Answers (1)

Abin
Abin

Reputation: 2956

Use The below Class for accepting commandparameters Using 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;
}

Usage:

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

obj is the command parameter passed in the above example.

Upvotes: 4

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