How to pass CommandParameters to the ViewModel? - silverlight

Question

I have a command that should switch the current view when it's executed. I binded this command to my buttons like this:
<Button Style="{StaticResource TextButton}" Command="{Binding ViewModel:MainViewModel.OpenItemCommand}" CommandParameter="{Binding Link}"/>
I want to pass Link (the link of the currently selected article) to my command. My command is defined like this:
public class Command : ICommand
{
public event EventHandler CanExecuteChanged;
readonly Predicate<Object> _canExecute;
readonly Action<Object> _executeAction;
public Command(Predicate<Object> canExecute, Action<object> executeAction)
{
_canExecute = canExecute;
_executeAction = executeAction;
}
public bool CanExecute(object parameter)
{
if (_canExecute != null)
return _canExecute(parameter);
return true;
}
public void UpdateCanExecuteState()
{
if (CanExecuteChanged != null)
CanExecuteChanged(this, new EventArgs());
}
public void Execute(object parameter)
{
if (_executeAction != null)
_executeAction(parameter);
UpdateCanExecuteState();
}
}
In my ViewModel I have this:
public ICommand OpenItemCommand
{
get
{
if (_openItemCommand == null)
{
_openItemCommand = new Command.Command(
p => true,
p => OpenItem(_HOW_DO_I_GET_THE_PARAMETER?_)
);
}
return _openItemCommand;
}
set
{
if (_openItemCommand != value)
{
_openItemCommand = value;
RaisePropertyChanged("OpenItemCommand");
}
}
}
private void OpenItem(Uri link)
{
throw new NotImplementedException();
}
When I create the command I need to pass the command parameter (the link) to the Execute method. But how do I get the value of this? I defined the CommandParameter in XAML, but I don't know how to access it.
I really searched through a huge amount of websites but I can't really find the answer.

Answer 1

You should look at the implementation of Prism's DelegateCommand or MVVM light's RelayCommand. With these you would write code like this:
public class ViewModel
{
public ViewModel()
{
OpenItemCommand = new RelayCommand<string>(OpenItem);
}
public RelayCommand<string> OpenItemCommand { get; private set; }
private void OpenItem(string link)
{
Debug.WriteLine(link);
}
}
where string in this case is the type of the parameter.
I'm not sure where the link parameter is coming from but if it's from a control, the value of the control could be bound to a property of your view model, then you don't need a parameter, for example:
public class ViewModel
{
public ViewModel()
{
OpenItemCommand = new RelayCommand(OpenItem);
}
public RelayCommand OpenItemCommand { get; private set; }
public string Link { get; set; }
private void OpenItem()
{
Debug.WriteLine(Link);
}
}

Answer 2

replace
p => OpenItem(_HOW_DO_I_GET_THE_PARAMETER?_)
with
p => OpenItem(p)
that is what the p stands for: parameter