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.

Answer 2

If you are that particular to pass elements to viewmodel You can use

 CommandParameter="{Binding ElementName=ManualParcelScanScreen}"

Answer 3

Just using Data Binding syntax. For example,

<Button x:Name="btn" 
         Content="Click" 
         Command="{Binding ClickCmd}" 
         CommandParameter="{Binding ElementName=btn,Path=Content}" /> 

Not only can we use Data Binding to get some data from View Models, but also pass data back to View Models. In CommandParameter, must use ElementName to declare binding source explicitly.

Answer 4

I personally simply use the .Tag attribute as follow:

<Button Content="Button" Click="Button_Click" Tag="{Binding .}"></Button>

Then in order to get the whole object:

private void Button_Click(object sender, RoutedEventArgs e)
    {
        var btn = sender as Button;
        var myViewModel = btn.Tag as MyViewModel;
        ...
    }