INotifyPropertyChanged未在ItemsControl内的ViewModel上触发

Question

I'm using ObservableCollection<MyItemViewModel> myItemVMList as the ItemsSouce . I am able to bind Command perfectly but the INotifyPropertyChanged isn't working. Here's my code:

public class MyItemViewModel: INotifyPropertyChanged {
    public event PropertyChangedEventHandler PropertyChanged;
    protected void OnPropertyChanged(string name) {
        PropertyChangedEventHandler handler = PropertyChanged;
        if (handler != null) {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }

    public MyItem MyItem { set; get; }

    private RelayCommand _ChangeMyItemPropertyValue;
    public ICommand ChangeMyItemPropertyValueCommand {
        get {
            if (_ChangeMyItemPropertyValue == null) _ChangeMyItemPropertyValue = new RelayCommand(o => ChangeMyItemPropertyValue());
            return _ChangeMyItemPropertyValue;
        }
    }
    private ChangeMyItemPropertyValue() {
        MyItem.SomeProperty = someDifferentValue;

        // NEITHER OF THESE CALLS WORK
        OnPropertyChanged("MyItem.SomeProperty");
        OnPropertyChagned("SomeProperty");
    }
}

Needless to say, the binding is set as Content="{Binding MyItem.SomeProperty}" inside the DataTemplate , and it shows the correct value. Problem is it isn't updated when I run the function.

SideNote: If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel .

Answer 1

If I implement the INotifyPropertyChanged inside MyItem it works, but I want it on the ViewModel

Yes, because that's how it's designed. How it's supposed to know it should listen to your ViewModel's property changed event? It doesn't bind to it, it binds to the model, so it listens to the changes on the model.

You have two choices basically:

• Implement INotifyPropertyChanged on MyItem

• Bind to the ViewModel

   Content="{Binding SomeProperty}" 

  And add a wrapper property:

   public string SomeProperty { get { return MyItem.SomeProperty; } set { MyItem.SomeProperty = value; OnPropertyChanged("SomeProperty"); } } 

  You should prefer binding to the ViewModel if you want to follow MVVM practices.

---

Side note: If you add [CallerMemberName] to OnPropertyChanged like this:

protected void OnPropertyChanged([CallerMemberName] string name = null) {
    var handler = PropertyChanged;
    if (handler != null)
        handler(this, new PropertyChangedEventArgs(name));
}

You'll be able to skip the property name altogether:

    public string SomeProperty
    {
        get { return MyItem.SomeProperty; }
        set
        {
            MyItem.SomeProperty = value;
            OnPropertyChanged(); // <-- no need for property name anymore
        }
    }