Pass command parameter to method in ViewModel in WPF?

Question

I am trying to pass CommandParameter to the method in my ViewModel. How to do this?

private void Open(object sender)
{
    if (sender==this.objMainWindow.btnHistory)
    {
        objMainWindow.Container.Child = objHistory;
    }

    if (sender == this.objMainWindow.btnNew_Item)
    {
        objMainWindow.Container.Child = objNewItem;
    }

    if (sender == this.objMainWindow.btnSide_Effects)
    {
        objMainWindow.Container.Child = objSideEffect;
    }
}

This is my meyhod in ViewModel that I want to pass CommandParameter. I use CommandParameter for button.

Answer 1

"ViewModel" implies MVVM. If you're doing MVVM you shouldn't be passing views into your view models. Typically you do something like this in your XAML:

<Button Content="Edit" 
        Command="{Binding EditCommand}"
        CommandParameter="{Binding ViewModelItem}" >

And then this in your view model:

private ViewModelItemType _ViewModelItem;
public ViewModelItemType ViewModelItem
{
    get
    {
        return this._ViewModelItem;
    }
    set
    {
        this._ViewModelItem = value;
        RaisePropertyChanged(() => this.ViewModelItem);
    }
}

public ICommand EditCommand { get { return new RelayCommand<ViewModelItemType>(OnEdit); } }
private void OnEdit(ViewModelItemType itemToEdit)
{
    ... do something here...
}

Obviously this is just to illustrate the point, if you only had one property to edit called ViewModelItem then you wouldn't need to pass it in as a command parameter.