Passing a parameter to ICommand

Question

I have a simple button that uses a command when executed, this is all working fine but I would like to pass a text parameter when the button is clicked.

I think my XAML is ok, but I'm unsure how to edit my RelayCommand class to receive a parameter:

<Button x:Name="AddCommand" Content="Add" 
    Command="{Binding AddPhoneCommand}"
    CommandParameter="{Binding Text, ElementName=txtAddPhone}" />

public class RelayCommand : ICommand
{
    private readonly Action _handler;
    private bool _isEnabled;

    public RelayCommand(Action handler)
    {
        _handler = handler;
    }

    public bool IsEnabled
    {
        get { return _isEnabled; }
        set
        {
            if (value != _isEnabled)
            {
                _isEnabled = value;
                if (CanExecuteChanged != null)
                {
                    CanExecuteChanged(this, EventArgs.Empty);
                }
            }
        }
    }

    public bool CanExecute(object parameter)
    {
        return IsEnabled;
    }

    public event EventHandler CanExecuteChanged;

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

score 13 · Accepted Answer · answered Oct 28 '12 at 20:20

13

Change Action to Action<T> so that it takes a parameter (probably just Action<object> is easiest).

private readonly Action<object> _handler;

And then simply pass it the parameter:

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

answered Oct 28 '12 at 20:20

McGarnagle

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Thanks that works great! I'm not that new to WPF but I am new to MVVM so commands are a new concept; but I can already see how they would help unit tests. So adding – Michael Harper Oct 28 '12 at 20:50
@MichaelHarper yes, exactly, a delegate that takes one object parameter. You can see they've defined multiple action types along those lines: http://msdn.microsoft.com/en-us/library/018hxwa8.aspx – McGarnagle Oct 28 '12 at 20:55
Thanks again, been a great help :D – Michael Harper Oct 28 '12 at 21:04

score 6 · Answer 2 · answered Jan 04 '18 at 00:08

6

You could just do

public ICommand AddPhoneCommand
{
    get
    {
        return new Command<string>((x) =>
        {
            if(x != null) { AddPhone(x); }
        };
    }
}

Then, of course have your AddPhone:

public void AddPhone(string x)
{
    //handle x
}

answered Jan 04 '18 at 00:08

Jud

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missing a closing parenthesis. `return new Command((x) => { if(x != null) { AddPhone(x); }});` – Vultuxe Aug 31 '21 at 15:43

score 3 · Answer 3 · answered May 26 '15 at 04:04

You can simply do this (no change to RelayCommand or ICommand required):

private RelayCommand _addPhoneCommand;
public RelayCommand AddPhoneCommand
{
    get
    {
        if (_addPhoneCommand == null)
        {
            _addPhoneCommand = new RelayCommand(
                (parameter) => AddPhone(parameter),
                (parameter) => IsValidPhone(parameter)
            );
        }
        return _addPhoneCommand;
    }
}

public void AddPhone(object parameter)
{
    var text = (string)parameter;
    ...
}

public void IsValidPhone(object parameter)
    var text = (string)parameter;
    ...
}

Passing a parameter to ICommand

3 Answers3

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