How to get the existing instance of DataContext in xaml ?

Question

How to get the existing instance of DataContext in xaml ?

maxime Hks 21

Hi,

Here is my problem

I have a ViewModel A (the vm for my main window) and a ViewModel B(vm for my second window).
And i need to get an object from my VM A to my VM B.

So what i did basicaly is putting parameter in my second window Constructor
then, in the behind code of this window, i manually created an instance of its viewModel, so i could put parameter in it as well.

In a nutshell, from my MainWindowVm

  `SecondWindow second = new SecondWindow (Object objectToBeSent);`

In the behind code of Second window :

`SecondWindowVm vm = new SecondWindowVm(objectToBeSent);`
`DataContext=vm;`

So, in order to make this working, i had to remove from my xaml the DataContext statement
as i always do like :

<Window.DataContext>
        <local:SecondWindowVM/>
    </Window.DataContext>

My bindings still works when i run my program even if Visual Studio tells me DataContext can't be found.
The question is : Is there a way to tell to my xaml that the DataContext is an existing instance of SecondWindowVm called "vm" ?

Thanks

Jack J Jun 25,296 Reputation points

2022-03-07T09:09:48.617+00:00

@maxime Hks , is any update? Please check if the following answers works for you.

Accepted answer

3 additional answers

Your answer

Jack J Jun 25,296 Reputation points

2022-03-07T09:09:48.617+00:00

@maxime Hks , is any update? Please check if the following answers works for you.

Answer 1

Hi,
you can use static class like in this code:

  public class ViewModelA
  {
    public ViewModelA() { if (StaticClass.DataRef == null) StaticClass.DataRef = new Data(); }
    public string Info
    {
      get => StaticClass.DataRef.Info;
      set { StaticClass.DataRef.Info = value; }
    }
  }
  public class ViewModelB
  {
    public ViewModelB() { if (StaticClass.DataRef == null) StaticClass.DataRef = new Data(); }
    public string Info
    {
      get => StaticClass.DataRef.Info;
      set { StaticClass.DataRef.Info = value; }
    }
  }
  public static class StaticClass
  {
    public static Data DataRef { get; set; }
  }

  public class Data
  {
    public string Info { get; set; }
  }

in first Window:

<Window.DataContext>
         <local:ViewModelA/>
</Window.DataContext>

in second Window:

<Window.DataContext>
         <local:ViewModelB/>
</Window.DataContext>

Answer 2

Karen Payne MVP 35,586 Volunteer Moderator

You need to reference the model in the xaml

xmlns:classes="clr-namespace:YourNamespace.Models"

Answer 3

maxime Hks 21

Thank you, that's a good idea

Answer 4

Anonymous

Hello,

Other simple way to directly access VM A in VM B is via application main window instance. use 'System.Windows.Application.Current.MainWindow.DataContext' to refer the view model instance of the VM A anywhere in your application.

Thanks, Bhushan

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How to get the existing instance of DataContext in xaml ?

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