Passing Command Parameters

Question

I'm trying to pass a command parameter with my command. I have commands in general working but passing a parameter doesn't seem to be going to well for me.

I'm trying to pass the UserName Property from the Hierarchical Data in my XAML. What am I doing wrong here.

I recieve and error trying to compile with the commands statement:

cannot convert from 'lambda expression' to 'System.Action'

<HierarchicalDataTemplate 
    DataType="{x:Type viewModel:UsersViewModel}" 
    ItemsSource="{Binding Children}">
    <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding UserName}">
            <TextBlock.ContextMenu>
                    <ContextMenu>
                        <MenuItem Header="Edit" Command="{Binding EditCommand}" CommandParameter="{Binding UserName}"/>
                        <MenuItem Header="Delete"/>
                    </ContextMenu>
                </TextBlock.ContextMenu>
        </TextBlock>
    </StackPanel>
</HierarchicalDataTemplate>

private RelayCommand _editCommand;
    public ICommand EditCommand
    {
        get
        {
            if (_editCommand== null)
            {
                _editCommand= new RelayCommand(param => this.LoadUser(object parameter));
            }
            return _editCommand;
        }
    }

    public void LoadUser(object username)
    {

    }

RelayCommand Class

public class RelayCommand : ICommand
{
    #region Fields

    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;

    #endregion // Fields

    #region Constructors

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

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
            throw new ArgumentNullException("execute");

        _execute = execute;
        _canExecute = canExecute;
    }
    #endregion // Constructors

    #region ICommand Members

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

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

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

Thanks for the help!

score 3 · Answer 1 · edited May 23 '17 at 12:02

3

You should not invoke the method, you should pass it as a parameter. Just replace new RelayCommand(param => this.LoadUser(object parameter)); for new RelayCommand(this.LoadUser);

Similar question here: RelayCommand lambda syntax problem

edited May 23 '17 at 12:02

Community

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1

answered Feb 06 '12 at 22:50

Felipe Castro

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10

score 3 · Accepted Answer · answered Feb 06 '12 at 22:51

3

new RelayCommand(param => this.LoadUser(object parameter));

Shouldn't this be:

new RelayCommand(param => this.LoadUser(param));

answered Feb 06 '12 at 22:51

H.B.

166,899
29
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1

@BatMasterson: There isn't much to those simple expessions, `Actions` are just void methods, the right side is the method body in which you just execute whatever you want to do. [`Funcs`](http://msdn.microsoft.com/en-us/library/bb534960.aspx) would be methods with return value. – H.B. Feb 06 '12 at 23:06

Passing Command Parameters

2 Answers2