WPF selectedItem on Menu or get commandparameter in viewmodel - wpf

Question

I am searching for hours to fix a simple problem. I wanted to work with "SelectedItem" on my menuItems, but after hours of stackoverflow I saw that's impossible. I found a lot about "CommandParameter" but I don't understand how it works.
This is what I want to do: I have a menu with "background1, background2,..." . If you select a background in the menu, I want to set that selected background as background.
It's a schoolproject, so we have to use MVVM and no codebehind is allowed.
How can I "use" the Commandparameter in my ViewModel?
This is my mainWindow.xaml:
<Toolbar>
<Menu>
<MenuItem Header="Background" ItemsSource="{Binding Backgrounds}">
<MenuItem.ItemTemplate>
<DataTemplate>
<MenuItem Header="{Binding Name}" Command="{Binding ChangeBackgroundCommand}" CommandParameter="{Binding Name}"/>
</DataTemplate>
</MenuItem.ItemTemplate>
</MenuItem>
</Menu>
</Toolbar>
This is a part of my mainWindowViewModel:
public MainWindowViewModel()
{
//load data
BackgroundDataService bds = new BackgroundDataService();
Backgrounds = bds.GetBackgrounds();
//connect command
WijzigBackgroundCommand = new BaseCommand(WijzigBackground);
}
private void ChangeBackground()
{
//I want here the name of the selected menuItem (by parameter?)
}
}
We use a baseCommand class(I don't want to change this class because its standard I think):
class BaseCommand : ICommand
{
Action actie;
public BaseCommand(Action Actie)
{
actie = Actie;
}
public event EventHandler CanExecuteChanged;
public bool CanExecute(object parameter)
{
return true;
}
public void Execute(object parameter)
{
actie.Invoke();
}
}
I use stackoverflow a lot :-) this is my firts post/question, I hope it's clear

Answer 1

Try this:
class BaseCommand<T> : ICommand
{
private readonly Action<T> _executeMethod = null;
private readonly Func<T, bool> _canExecuteMethod = null;
public BaseCommand(Action<T> executeMethod)
: this(executeMethod, null)
{
}
public BaseCommand(Action<T> executeMethod, Func<T, bool> canExecuteMethod)
{
_executeMethod = executeMethod;
_canExecuteMethod = canExecuteMethod;
}
public bool CanExecute(T parameter)
{
if (_canExecuteMethod != null)
{
return _canExecuteMethod(parameter);
}
return true;
}
public void Execute(T parameter)
{
if (_executeMethod != null)
{
_executeMethod(parameter);
}
}
public event EventHandler CanExecuteChanged;
bool ICommand.CanExecute(object parameter)
{
if (parameter == null &&
typeof(T).IsValueType)
{
return (_canExecuteMethod == null);
}
return CanExecute((T)parameter);
}
void ICommand.Execute(object parameter)
{
Execute((T)parameter);
}
}
Use it like this:
public MainWindowViewModel()
{
// ...
// connect command
WijzigBackgroundCommand = new BaseCommand<YourBackgroundClass>(
(commandParam) => WijzigBackground(commandParam),
(commandParam) => CanWijzigBackground(commandParam));
}
private void WijzigBackground(YourBackgroundClass param)
{
// Use 'param'
}
private bool CanWijzigBackground(YourBackgroundClass param)
{
// Use 'param'
}