Execute Method from Codehind using ViewModel WPF - wpf

Question

I've abandoned the MVVM midway through app development just to get this app out.
I've written a method in the code behind to update the database/datagrid etc.
My application navigation is using Commands to the ViewModel firing some event but never touches the code-behind except one time to initialize the class.
So basically I push the button one time and it works with the default initial setting but I can't call my code-behind Update() method anymore once the view as been intialized.
How can I call this code-behind method from the view model?
Thanks!!
Update code
//Navigation ViewModel
//PaneVm.cs
public CommandExtension NewAssignmentCommand { get; set; }
private void CreateCommands()
{
NewAssignmentCommand = new CommandExtension(NewAssignment, CanNewAssignment);
}
GlobalCommands.NewAssignmentCommand = NewAssignmentCommand;
private bool CanNewGroupAssignment(object obj)
{
return true;
}
private void NewGroupAssignment(object obj)
{
OnPropertyChanged("NewGroupAssignmentCommand");
}
//MainVM.cs
// [Events]
void _PaneVm_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == "NewGroupAssignmentCommand")
WorkspaceVm.CurrentVm = new NewAssignmentsVm();
}
//NewAssignmentVm.cs
//Constructor
public NewAssignmentsVm()
{
var rc = new RepositoryContext();
_RoResearchers = new ObservableCollection<Researcher>(rc.ResearcherData.GetAllResearchers());
_QuarterDateTime = DateTime.Now;
CreateCommands();
}
//NewAssignment.cs
//Code-behind
//The method
private void UpdateGrid()
{
report_datagrid.ItemsSource = null;
using (var rc = new RepositoryContext())
{
if (quarter_datepicker.SelectedDate != null)
{
if (!String.IsNullOrEmpty(reportType))
researchers = rc.ResearcherData.GetResearchersWeeksByQuarter(Convert.ToDateTime(quarter_datepicker.SelectedDate), reportType).ToList();
}
}
}
UPDATE 2:
I solved my problem based off this answer. I created a Global Action
public static class GlobalCommands
{
public static Action UpdateGrid { get; set; }
}
Then in my code-behind constructor I set the value public
MyCodeBehind()
{
GlobalCommands.UpdateGrid = new Action(() => this.UpdateGrid());
}
Didn't need to bind to the context again. Everything else was the same. Thank you

Answer 1

Main idea is:
class MyCodeBehind
{
public MyCodeBehind()
{
Action action = new Action(()=> this.SomeMethodIWantToCall());
var myVM = new MyVM(action); // This is your ViewModel
this.DataContext = myVM;
}
private void SomeMethodIWantToCall(){...}
}
class MyVM
{
private Action action;
public MyVM(Action someAction)
{
this.action = someAction;
}
private void SomeMethodInVM()
{
this.action(); // Calls the method SomeMethodIWantToCall() in your code behind
}
}

Answer 2

Instead of letting code-behind know about viewmodel, You can make use of NotifyOnSourceUpdated in your xaml binding.
Something like this:
<TextBlock Grid.Row="1" Grid.Column="1" Name="RentText"
Text="{Binding Path=Rent, Mode=OneWay, NotifyOnTargetUpdated=True}"
TargetUpdated="OnTargetUpdated"/>
Here, 'OnTargetUpdated' is a handler in your code behind. This handler will be invoked when "Rent" property of ViewModel is changed.
Details at MSDN