Pass parameter with a command into the viewmodel

Question

I have trouble sending a parameter from my view to my viewmodel.

View.xaml:

In my view, I have the following:

<TextBox
    MinWidth="70"
    Name="InputId"/>

<Button 
    Command="{Binding ButtonCommand}"
    CommandParameter="{Binding ElementName=InputId}"
    Content="Add"/>

View.xaml.cs:

public MyView()
{
    InitializeComponent();
}

public MyView(MyViewModel viewModel) : this()
{
    DataContext = viewModel;
}

MyViewModel.cs:

public class MyViewModel : BindableBase
{
    public ICommand ButtonCommand { get; private set; }

    public MyViewModel()
    {
        ButtonCommand = new DelegateCommand(ButtonClick);
    }

    private void ButtonClick()
    {
        //Read 'InputId' somehow. 
        //But DelegateCommand does not allow the method to contain parameters.
    }
}

Any suggestions to, how I can pass the InputId when I click the button to my viewmodel?

Mr Lister · Accepted Answer · 2016-02-29 16:25:28Z

11

You need to add <object> to your delegate command like this :

public ICommand ButtonCommand { get; private set; }

     public MyViewModel()
        {
            ButtonCommand = new DelegateCommand<object>(ButtonClick);
        }

        private void ButtonClick(object yourParameter)
        {
            //Read 'InputId' somehow. 
            //But DelegateCommand does not allow the method to contain parameters.
        }

Do you want to get the text of textbox change your xaml to :

CommandParameter="{Binding Text,ElementName=InputId}"

edited Feb 29, 2016 at 16:25

Mr Lister

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answered Feb 25, 2016 at 11:13

user5747953

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2 Comments

Rasmus Bækgaard Over a year ago

This is perfect! Thank you.

dvdhns Over a year ago

After googling for 30 minutes, this was by far the best explanation. Thanks!

Nawed Nabi Zada · Accepted Answer · 2016-02-25 11:27:23Z

For proper implementation of ICommand/RelayCommand have a look at this MSDN page.

Summary:

public class RelayCommand : ICommand
{
    readonly Action<object> _execute;
    readonly Func<bool> _canExecute;

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

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

        _execute = execute;
        _canExecute = canExecute;
    }


    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute.Invoke();
    }

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

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

} 


public MyViewModel()
{
    ButtonCommand = new RelayCommand(ButtonClick);
}

private void ButtonClick(object obj)
{
    //obj is the object you send as parameter.
}

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