MVVM Light pass parameters to child view model - wpf

Question

I am new to MVVM and WPF.
I am using MVVM Light to make an application which contains a DataGrid within a window, which has a view model (MainViewModel) and another window for adding and editing records in the DataGrid, that also has its own view model (EditViewModel).
What I am worried about is the approach I am using to open the Add/Edit window from the MainViewModel. In the MainViewModel I have a property SelectedItem, which is bound to the SelectedItem property of the DataGrid and an IsEdit boolean property that indicates if the Add/Edit window should be launched in Add or Edit mode.
When the Add/Edit window gets opened in edit mode, in the constructor of its view model I have the following line:
MainViewModel mainViewModel = ServiceLocator.Current.GetInstance<MainViewModel>();
That obviously retrieves the current instance of the MainViewModel, which works perfectly fine, but I am not really sure it is the best way to do this.
Also if I have more than one instances of the Main window, that use the same MainViewModel instance and I open an instance of the Add/Edit window from both of them, the Add/Edit windows are going to get data from the same instance of the MainViewModel which may be a problem.
If I try to create a new instance of MainViewModel for each MainWindow I open, then I don't know how to pass the instance of the currently used MainViewModel to the EditViewModel.
I hope I made clear what I need to do. Tell me if I have missed something and I will add it:)
Thanks in advance

Answer 1

Hi if I havent misunderstood your problem incorrect you can do it this way:
Since i need IsRequired dependency Property in both MainView and EditView i created a class that extends Window class
public class ExtendedWindow:Window
{
public static readonly DependencyProperty IsRequiredProperty = DependencyProperty.Register("IsRequired", typeof(bool), typeof(ExtendedWindow));
public bool IsRequired
{
get { return (bool)GetValue(IsRequiredProperty); }
set { SetValue(IsRequiredProperty, value); }
}
}
MainView and ViewModel
public partial class MainWindow:ExtendedWindow
{
public MainWindow()
{
InitializeComponent();
DataContext = new MainViewModel();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
EditView editView = new EditView();
**((EditViewModel)editView.DataContext).IsRequired = this.IsRequired;**
editView.Show();
}
}
public class MainViewModel : INotifyPropertyChanged
{
public MainViewModel()
{
IsRequired = true;
}
private bool isRequired;
public bool IsRequired
{
get { return isRequired; }
set { isRequired = value; Notify("IsRequired"); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void Notify(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
EditView and ViewModel
public partial class EditView:ExtendedWindow
{
public EditView()
{
InitializeComponent();
DataContext = new EditViewModel();
}
}
public class EditViewModel : INotifyPropertyChanged
{
private bool isRequired;
public bool IsRequired
{
get { return isRequired; }
set { isRequired = value; Notify("IsRequired"); }
}
public event PropertyChangedEventHandler PropertyChanged;
private void Notify(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
This is just kind of dummy but can give you idea how you can do it. I have tried it in dummy and its working fine.