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Good morning companions. I would like to know how I can modify the DataContext of a view with its ViewModel, from another ViewModel or from the same ViewModel.

The program is a test to be used later in another project. Basically they are two UserControl inside a window, each with its respective ViewModel. Implement the INotifyPropertyChanged and ICommand interfaces with NotifyBase and RelayCommand.

In view1

<Button Grid.Column="0" Margin="30" Height="120"    CommandParameter="Button1ViewModelIzdo" Command="{Binding Btn1Command}">

In ViewModel1:

public class Window1ViewModel : NotifyBase
 public delegate void EventHandler(object sender, CustomEventArgs e);
 public event EventHandler ThrowEvent;// = delegate { };

 private ICommand _btn1Command;
 public ICommand Btn1Command
         return _btn1Command ?? (_btn1Command = new  RelayCommand((parameter) => Bnt1Action(parameter)));

 private void Bnt1Action(object parameter)
     String msg = parameter as String;
     ThrowEvent?.Invoke(this, new CustomEventArgs(msg));

In View2

<TextBlock TextAlignment="Center" x:Name="Data" Text="{Binding   Path=Data,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"></TextBlock

In ViewModel2

public class Window2ViewModel : NotifyBase
    private Window1ViewModel _Thrower;

    public Window2ViewModel()
        _Thrower = new Window1ViewModel();
        _Thrower.ThrowEvent += ( emisor, e) => { ChangeData(emisor , e);      };

    private string _data;

    public string Data
        get { return _data; }
                if (_data != value)
                    _data = value;

    private void ChangeData(object emisor, CustomEventArgs e)
        Data = e.msg;

The CustomEventArgs class has a msg propedad. But the event does not launch. What am I doing wrong ?

Many thanks in advance. Greetings César.

What I have tried:

Use delegates and events Search for examples in stackoverflow and codeproject
Dirk Bahle 8-Sep-18 4:54am    
Hi I am not sure what your exact question is but you should research behaviors

or 'attached behaviors' if you want to propagate events from a WPF control to the viewmodel using command binding (if you cannot change the source code of the control)
cesar.iriso 8-Sep-18 4:58am    
Thans Dirk. I'm reading a .
It seems that it is not a good idea to associate ViewModels with UserControl
Greeting César.
Dirk Bahle 8-Sep-18 10:50am    
An association between viewmodel and usercontrol via datacontext is in principal OK - but there are technical reasons why events/commands should be with their particular patterns ...
Dirk Bahle 8-Sep-18 10:57am    
Not sure if it helps, but it might be something to consider.
Here is an example of a control that will watch the DataContextChanged event and attach itself to a viewmodel that implements the IEditBox interface:

Doing so allows the viewmodel to bubble notifications through the control. This means the viewmodel does not have to worry about the UI part of the notification - its worring about the required event only ...
cesar.iriso 8-Sep-18 15:38pm    
Too complex for me, I'm a little newbie :)
Thank you anyway.

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