how to pass property value to property of another class in wpf mvvm

Question

I want to pass SecondViewModel SecondProperty value to ViewModel myProperty and show the value on TextBlock. i want the codi

Answer 1

From your comment, assuming that ViewModel holds a collection of SecondViewModel items, you need to set the PropertyChangedEvent for each instance of SecondViewModel to trigger ViewModel.myProperty to refresh. e.g. ...

public class ViewModel
{
    private List _secondViewModels = new List();

    public IEnumerable SecondViewModels => _secondViewModels;

    public int myProperty => _secondViewModels.Sum(vm => vm.SecondProperty);

    public void AddSecondViewModel(SecondViewModel vm)
    {
        _secondViewModels.Add(vm);
        vm.PropertyChanged += (s, e) => OnPropertyChanged(nameof(myProperty));
        OnPropertyChanged(nameof(myProperty));
    }
}

As an aside, you should never call OnPropertyChanged() with a "magic string" - use nameof() instead.