How to change the appearance and state of an object from a ViewModel?

Question

WPF

Good afternoon!
I am mastering the template MVVMand faced such a problem: there is one UserControlthat contains 2 text blocks and a switch. The switch is also UserControl, has 2 states (on and off), looks more or less similar to the switch in Windows 10. When you click on the switch, its switching animation starts, and its current state is stored in a private variable. An event is used to change the state and appearance of the switch MouseLeftButtonDown.
Question : how can I MVVMchange the appearance and state of the switch from ViewModel? I need to be able to change the appearance and state of the switch and clicking on it and from ViewModel.
Thank you.

update: After I formulated and asked the question, it became clear how to solve the problem. The duck method works. To change the appearance or state of an object, you can bind a method to a DependencyProperty.

Switch object model:

public class SwitchBarModel : INotifyPropertyChanged
    {
        private bool switchState = default(bool);

        public bool SwitchState
        {
            get => switchState;
            set
            {
                switchState = value;
                OnPropertyChanged("SwitchState");
            }
        }      

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

Code-behind UserControl Switch:

public bool State
        {
            get { return (bool)GetValue(StateProperty); }
            set { SetValue(StateProperty, value); }
        }

        // Using a DependencyProperty as the backing store for State.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty StateProperty =
            DependencyProperty.Register("State", typeof(bool), typeof(Switch), new PropertyMetadata(<b>OnStateChanged</b>));

        private static void <b>OnStateChanged</b>(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
          <b> // Первой строкой обязательно приводим объект к нужному типу и вызываем нужный метод</b>
            (d as Switch).ChangeState();
        }

        internal void ChangeState()
        {
            // Выполняем нужные действия по изменению внешнего вида или состояния
        }

Now, all that's left is to change the property SwitchStateof the desired element. In my case, the state is changing in the collection from the ViewModel.

Fragment ViewModel:

SwitchCollection.Where(s => s.SwitchState == false)
.ToList()
.ForEach(s =>
{
   s.SwitchState = true;
});

Forgive me WPF gurus!

Answer 1

You implement the property through the DependecyProperty of the switch and bind it to the
ViewModel. https://docs.microsoft.com/en-us/dotnet/framework/...